Coherently strained (al xgroupiii1-x)n / group IIIN / (al xgroupiii1-x)n quantum-well heterostructures with compensation doping for hemts

Abstract

Designs for metal polar materials, which incorporate n-type compensation doping in the strained QW to counter the negative polarization effect at the (AlxGroupIIIN(1-x))N / Group IIIN interface and reduce the internal electric field in the well are presented. Designs for Nitrogen polar materials, which incorporate p-doping to compensate for the 2DEG at the bottom interface, are disclosed.

Description

Docket No.: 11208-02COHERENTLY STRAINED (Al xGROUPIIIl-x)N / GROUP IIIN / (A1 xGROUPIIIl-x)N QUANTUM-WELL HETEROSTRUCTURES WITH COMPENSATION DOPING FOR HEMTsCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application Serial No.63 / 674,129, filed July 22, 2024, entitled COHERENTLY STRAINED (Al xGROUPHIl-x)N / GROUP HIN / (A1 xGROUPHIl-x)N QUANTUM- WELL HETEROSTRUCTURES WITH COMPENSATION DOPING FOR HEMTs, which is incorporated herein by reference in its entirety and for all purposes.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with U.S. Government support from the U.S. Air Force under Air Force Office of Scientific Research (AFOSR) Award Number: FA9550-20-1-0148, from the U.S. Army under Army Research Office Grant No. W911NF2220177, from the National Science Foundation under NSF MRSEC program, grant No. DMR-1719875 and under NSF grant No. MRI DMR-1631282 . The U.S. Government has certain rights in the invention.BACKGROUND

[0003] These teachings relate generally to (AlxGroupIII(i-X))N / GroupIIIN / (AlyGroupIII(i y))N Quantum-Well Heterostructures, and, more particularly, to (AlxGroupllI(]X))N / Group IIIN / (AlyGroupIII(i y))N Quantum-Well Heterostructures with Compensation Doping for High-Electron-Mobility Transistors.

[0004] Since there is a rich literature for AlN / GaN / AlN quantum-well heterostructures, results are presented below for AlN / GaN / AlN quantum-well heterostructures. AlN-based quantumwell (QW) high-electron-mobility transistors (HEMTs) have emerged as a new platform for high-power, high-frequency amplifiers due to their tight carrier confinement, high breakdown electric fields, and high thermal conductivity to efficiently dissipate heat from the channel layer. This structure consists of a thin GaN QW (~ 20 nm) surrounded by a thick AIN buffer (~ 500 nm) and top AIN barrier (~ 5 nm). The large polarization discontinuity between AIN and GaN induces two-dimensional electron gas (2DEG), which is further confined by the QW due to the large conduction band offset at the AlN / GaN heterojunction. Simultaneously, a two-dimensional hole gas (2DHG) coexists in the same QW at the bottom GaN / AlN interface, which is confined by the valence bandDocket No.: 11208-02offset between AIN and GaN. The performance of AlN / GaN / AlN HEMTs is further enhanced when grown on single-crystal AIN substrates, benefiting from their low dislocation density and the absence of thermal boundary resistance with the substrates.

[0005] However, 2DEGs in AlN / GaN / AlN QW HEMTsl 1-14 have exhibited lower room temperature (RT) electron mobilities in comparison to Al(Ga)N / GaN HEMTs, which typically exhibit RT electron mobility around 1900 cnr / Vs with 2DEG density lower than or around IxlO13cm-2. These lower mobilities are limited by scattering, which is exacerbated by the strong internal electric field in the well. In addition, the presence of 2DHG on the opposite side of the well could influence the measured apparent electron mobilities through parallel conduction. When the bilayers are in proximity, Coulomb drag might result in electron-hole scattering in the narrow wells. In a recent work, the effect of vertical electric field on the transport properties of QW HEMTs was investigated. The vertical electric field in the QW decreases as QW thickness increases. The reduction in the internal electric field shifts the 2DEG centroid away from the interface, consequently decreasing the impact of interface roughness (IR) scattering. By increasing the thickness of the QW to its relaxed form, we achieved a RT mobility over 1000 cm2 / Vs in a binary QW HEMTs. However, this approach incurred penalties such as the relaxation of GaN channel and the formation of defects.

[0006] There is a need for designs that do not incur penalties, such as the relaxation of GaN channel and the formation of defects.BRIEF SUMMARY

[0007] Designs for metal polar materials, which incorporate n-type compensation doping in the strained QW to counter the negative polarization effect at the (AlxGroupIlI(iX))N / Group 111N interface and reduce the internal electric field in the well are presented. Designs for Nitrogen polar materials, which incorporate p-doping to compensate for the 2DEG at the bottom interface, are also presented.

[0008] In one instantiation, the semiconductor quantum well structure of these teachings includes a metal polar first layer; a material of the metal polar first layer including one of AIN, AlxGai xN, AlxIni xN. AlxScixN, AlxBixN, AlxYi.xN, or AlxLai.xN, a metal polar second layer of Group IIIN material epitaxially deposited on the metal polar first layer, at least one the metal polar first layer or the metal polar second layer having an n-doped section, and a metal polar third layer epitaxially deposited on the metal polar second layer of Group IIIN material. A material of the metal polar third layer includes at least one of AIN, AlxGaixN, AlxIxN, AlxSci.xN, AlxBi.xN, A1XY].XN, or AlxLai-xN. A thickness of the metal polar first layer and the material of the metal polar first layer and a thickness of the second metal polar layer of Group IIIN material are selected such that, inDocket No.: 11208-02absence of the n-doped section, at the interface between the metal polar first layer and the second metal polar layer of Group IIIN material, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A thickness of the third metal polar layer and the material of the third metal polar layer and the thickness of the second metal polar layer of Group IIIN material are selected such that, at an interface between the second metal polar layer of group III material and the third metal polar layer, a net positive polarization charge induces a 2D electron gas (2DEG). A density of the n-doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form the interface between the metal polar first layer and the second metal polar layer of Group IIIN material.

[0009] In another instantiation, the semiconductor quantum well structure of these teachings includes a nitrogen polar-first layer, a material of the nitrogen polar first layer including one of AIN, AlxGai xN, AlxIni xN, AlxScixN, AlxBrxN , AlxYrxN, or AlxLarxN, a second nitrogen polar layer of Group IIIN material epitaxially deposited on the nitrogen polar first layer, at least one of the nitrogen polar first layer or the second nitrogen polar layer being p-doped, and, a nitrogen polar third layer epitaxially deposited on the second nitrogen polar-layer, a material of the nitrogen polar-third layer including one of AIN, AlxGaixN, AlxInixN, AlxSci.xN, AlxBrxN, AlxYj.xN, or AlxLaixN. A thickness of the nitrogen polar first layer and the material of the nitrogen polar first layer and a thickness of the second nitrogen polar layer of Group IIIN material are selected such that, in absence of p-doping, at the interface between the nitrogen polar first layer and the second nitrogen polar layer of Group IIIN material, net positive polarization charge is sufficient to induce a 2D electron gas (2DEG). A thickness of the third nitrogen polar-layer and the material of the third nitrogen polar layer and the thickness of the second nitrogen polar layer of Group IIIN material are selected such that, at an interface between the second nitrogen polar layer of group III material and the third nitrogen polar layer, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A density of the p-doping is selected such that the 2DEG is suppressed.

[0010] In yet another instantiation, the semiconductor quantum well structure of these teachings includes a nitrogen polar-first layer, a material of the nitrogen polar first layer including at least one of AIN, AlxGaixN, AlxInrxN, AlxSc].xN, A1XB].XN, A1XY|.XN, or AlxLarxN, a nitrogen polar second layer of Group IIIN material epitaxially deposited on the nitrogen polar first layer, and a nitrogen polar third layer epitaxially deposited on the second nitrogen polar layer. A material of the third nitrogen polar layer includes one of AIN, AlxGaixN, AlxIni-xN, AlxScixN, A1XB|.XN, AlxYi-xN, or AlxLai-xN. At least one of the nitrogen polar third layer or the nitrogen polar second layer has an n-doped section. A thickness of the nitrogen polar first layer and the material of the nitrogen polar first layer and a thickness of the second nitrogen polar layer of Group IIIN material are selected such that,Docket No.: 11208-02at the interface between the nitrogen polar first layer and the second nitrogen polar layer of Group IIIN material, net positive polarization charge is sufficient to induce a 2D electron gas (2DEG). A thickness of the third nitrogen polar layer and the material of the nitrogen polar third layer and the thickness of the nitrogen polar-second layer of Group IIIN material are selected such that, at an interface between the nitrogen polar-second layer of group III material and the nitrogen polar third layer, in the absence of n-doping, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A density of the n-doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form the interface between the nitrogen polar third layer and the nitrogen polar second layer of Group IIIN material.

[0011] In one instantiation, the method of these teachings for fabricating a semiconductor quantum well structure includes epitaxially depositing a metal polar first layer on a substrate, a material of the metal polar first layer including one of AIN. AlxGai.xN, AlxInixN, AlxSci.xN, AlxBi.XN, AlxYiXN, or AlxLaiXN, epitaxially depositing a metal polar second layer of Group IIIN material on the metal polar first layer, n-doping one of a section of the material of the metal polar first layer or a section of the material of the metal polar-second layer, epitaxially depositing a metal polar third layer on the metal polar second layer of Group IIIN material. A material of the metal polar third layer includes at least one of AIN, AlxGaixN, AlxInixN, AlxSci.xN, AlxBixN, AlxYi-xN, or AlxLauxN. A thickness of the metal polar first layer and the material of the metal polar first layer and a thickness of the second metal polar-layer of Group IIIN material are selected such that, in absence of the n-doped section, at the interface between the metal polar first layer and the second metal polar layer of Group IIIN material, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A thickness of the third metal polar-layer and the material of the third metal polar layer and the thickness of the second metal polar layer of Group IIIN material are selected such that, at an interface between the second metal polar layer of group III material and the third metal polar layer, a net positive polarization charge induces a 2D electron gas (2DEG). A surface density of the n-Delta doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form the interface between the metal polar first layer and the second metal polar layer of Group IIIN material.

[0012] In another instantiation, the method of these teachings for fabricating a semiconductor quantum well structure includes epitaxially depositing a nitrogen polar first layer on a substrate; a material of the nitrogen polar first layer includes one of AIN, AlxGaixN, AlxIni-xN, AlxScj.xN, AlxBi-xN, AlxYi_xN, or AlxLai-xN, epitaxially depositing a second nitrogen polar layer of Group IIIN material on the nitrogen polar first layer, at least one the nitrogen polar first layer or the second nitrogen polar layer being a p-doped layer, and epitaxially depositing a third nitrogen polarDocket No.: 11208-02layer on the second nitrogen polar layer, a material of the third nitrogen polar layer comprising one of AIN, AlxGajxN, AlxInixN, AlxScixN, AlxBixN, AlxYi-xN, or AlxLaixN. A thickness of the nitrogen polar first layer and the material of the nitrogen polar first layer and a thickness of the second nitrogen polar-layer of Group IIIN material are selected such that, in absence of p-doping, at the interface between the nitrogen polar first layer and the second nitrogen polar-layer of Group IIIN material, net positive polarization charge is sufficient to induce a 2D electron gas (2DEG). A thickness of the third nitrogen polar layer and the material of the third nitrogen polar layer and the thickness of the second nitrogen polar layer of Group IIIN material are selected such that, at an interface between the second nitrogen polar layer of group III material and the third nitrogen polar layer, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A density of the p-doping is selected such that the 2DEG is suppressed.

[0013] In yet another instantiation, the method of these teachings for fabricating a semiconductor quantum well structure includes epitaxially depositing a nitrogen polar first layer, a material of the nitrogen polar first layer including at least one of AIN, AlxGarxN, AlxInrxN, AlxSci¬ xN, AlxBi-xN, A1XY]XN, or AlxLai xN, epitaxially depositing a nitrogen polar-second layer of Group IIIN material on the nitrogen polar first layer, epitaxially depositing a nitrogen polar third layer on the second nitrogen polar layer, a material of the third nitrogen polar layer including one of AIN, AlxGarXN. AlxIni.xN, AlxSci xN. AlxBrxN, AlxYi.xN. or AlxLai.xN. n-doping one of a section of the material of the nitrogen polar third layer or a section of the material of the nitrogen polar third layer. A thickness of the nitrogen polar first layer and the material of the nitrogen polar first layer and a thickness of the second nitrogen polar layer of Group IIIN material are selected such that, at the interface between the nitrogen polar first layer and the second nitrogen polar layer of Group IIIN material, net positive polarization charge is sufficient to induce a 2D electron gas (2DEG). A thickness of the third nitrogen polar layer and the material of the nitrogen polar third layer and the thickness of the nitrogen polar second layer of Group IIIN material are selected such that, at an interface between the nitrogen polar second layer of group III material and the nitrogen polar third layer, in the absence of n-6-doping, a net negative polarization charge is sufficient to induce a 2D hole gas. (2DHG). A density of the n-doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form at the interface between the nitrogen polar third layer and the nitrogen polar second layer of Group IIIN material.

[0014] A number of other instantiations ae also disclosed.

[0015] For a better understanding of the present teachings, together with other and further objects thereof, reference is made to the accompanying drawings and detailed description, and its scope will be pointed out in the appended claims.Docket No.: 11208-02BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 shows an instantiation of the quantum well structure of these teachings;

[0017] Figure 1A is a schematic of an epitaxial undoped AlN / GaN / AlN QW HEMT structure;

[0018] Figure IB shows one instance of the instantiation of the quantum well structure of these teachings of Fig. 1 , a 8-doped AlN / GaN / AlN QW HEMT, which incorporates a sheet of silicon donors sc,;

[0019] Figures 1C, ID show simulated energy-band diagrams of the undoped and 6-doped QW HEMTs, respectively;

[0020] Figures IE, IF show the simulated carrier density of the undoped and 8-doped QW HEMTs, respectively;

[0021] Figure 1G shows another instantiation of the quantum well structure of these teachings;

[0022] Figure 1H shows an instantiation of a metal polar quantum well structure of these teachings in which the third layer includes an AIN interlayer and a sub-layer;

[0023] Figure 2A shows Measured (solid lines) and simulated (dashed lines) Omega / 2Theta scans across the symmetr ic (002) reflection for both the undoped and 8-doped QW HEMTs, confirming the target thickness and sharp interfaces;

[0024] Figures 2B-2C show reciprocal space maps (RSM) around the asymmetric (-105) reflection for the undoped and 8-doped QW HEMTs, respectively;

[0025] Figures 2D-2E show 10 x 10 jm2and 2 x 2 jm2AFM scans of the as-grown undoped and 8-doped QW HEMTs, respectively, showing atomic steps and smooth surface morphologies;

[0026] Figures 3A-3C show temperature-dependent (a) 2DEG density, (b) electron mobility, and (c) sheet resistance for both the undoped (black circles) and 8-doped (blue circles) QW HEMTs.;

[0027] Figure 4 shows a Benchmark comparison of 2DEG density and room temperature mobility for 8-doped QW HEMTs with the previously reported metal-polar binary AlN / GaN / AlN Heterostructure;

[0028] Figure 4A shows a high-electron-mobility transistor (HEMT) including an instantiation of the quantum well structure of these teachings;

[0029] Figure 4B shows an instance of the instantiation of the quantum well structure of these teachings shown in Fig. 1G;

[0030] Figure 4C shows another high-electron-mobility transistor (HEMT) including the instantiation of the quantum well structure of these teachings shown in Fig. 4B ;Docket No.: 11208-02

[0031] Figure 4D shows yet another high-electron-mohility transistor (HEMT) including the instantiation of the quantum well structure of these teachings shown in Fig. IB;

[0032] Figure 4E shows contact resistance (7?c) and sheet resistance <7?Sh) measurements for the instantiation of the HEMT shown in Fig. 4D;

[0033] Figure 4F shows the representative output characteristics of the instantiation of the HEMT shown in Fig. 4D;

[0034] Figure 4G shows the transfer characteristics of the HEMT shown in Fig. 4D;

[0035] Figure 4H shows the small-signal unilateral gain (U), current gain (I / 121I2), maximum stable gain (MSG), and maximum available gain (MAG) of the HEMT shown in Fig. 4D;

[0036] Figure 4H shows the small-signal unilateral gain (U), current gain (I / 22112), maximum stable gain (MSG), and maximum available gain (MAG) for the HEMT shown in Fig. 4D;

[0037] Figure 41 shows pulsed current-voltage (ZD - VDS) measurements for the HEMT shown in Fig. 4D;

[0038] Figure 4J shows CW large-signal measurements performed on the HEMT shown in Fig. 4D;

[0039] Figure 4K benchmarks the large-signal performance of the HEMT shown in Fig. 4D in terms of Pout as a function of GaN channel thickness (GaN thickness between the top and the bottom barrier);

[0040] Figure 4L shows Poutof metal-polar, single-channel GaN HEMTs, including but not limited to double-heterostructure HEMTs, plotted against Vosqin the frequency range from 8 to 12 GHz (XHEMT is the HEMT shown in Fig. 4D);

[0041] Figure 4M shows the associated Poutat peak PAE of AIN XHEMTs compared with those of GaN HEMTs in Figure 4L (XHEMT is the HEMT shown in Fig. 4D);

[0042] Figure 5 shows a flowchart representation of an instantiation of the method of these teachings;

[0043] Figure 5A shows a flowchart representation of an instance of the instantiation of the method of these teachings shown in Fig. 5;

[0044] Figures 6A and 6B show a comparison of polarization charge in Metal polar and Nitrogen polar structures;

[0045] Figure 7 shows a schematic of a further instantiation of the quantum well structure of these teachings;

[0046] Figure 7 A shows a schematic of yet another instantiation of the quantum well structure of these teachings;Docket No.: 11208-02

[0047] Figure 8 shows a flowchart representation of another instantiation of the method of these teachings;

[0048] Figure 8A shows a flowchart representation of a further instantiation of the method of these teachings;

[0049] Figure 9 shows a schematic of yet another instantiation of the quantum well structure of these teachings;

[0050] Figure 9A shows a schematic of yet another instantiation of the quantum well structure of these teachings;

[0051] Figure 9B shows a schematic of an instance of still another instantiation of the quantum well structure of these teachings;

[0052] Figure 9C shows one instance of the instantiation of the quantum well structure of these teachings of Fig.9A;

[0053] Figure 9D shows an instantiation of a nitrogen polar quantum well structure of these teachings in which the first layer includes an AIN interlayer and a sub-layer;

[0054] Figure 10 shows a flowchart representation of yet another instantiation of the method of these teachings; and

[0055] Figure 10A shows a flowchart representation of an instance of the instantiation of the method of these teachings shown in Figure 10.DETAILED DESCRIPTION

[0056] The following description is made for the purpose of illustrating the general principles of the present teachings and is not meant to limit the inventive concepts claimed herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations.

[0057] As additionally used herein, the term “about,” when combined with a value, refers to ±10% of the value.

[0058] "Group III," as used herein, refers to a group of elements in the periodic table including what are now called Group 13 elements: boron (B), aluminum (Al), gallium (Ga), indium (In), thallium (Tl).

[0059] "Group IIIN," as used herein, refers to one of GaN, InN, and combinations thereof, such as (GaxIni.x)N, (AlxGai-x)N, or (AlxIni-x)N.Docket No.: 11208-02

[0060] “3- doping (or Delta doping),’” as used herein, refers to doping distributions in semiconductors that are scaled down in one dimension to their ultimate spatial limit, the dopants being confined to a single or few monolayers of the semiconductor lattice. (Sec, for example, E.F. Schubert, Chapter 1 Delta-Doping of Semiconductors: Electronic, Optical, and Structur al Properties of Materials and Device, Semiconductors and Semimetals, Volume 40, 1994, Pages 1-151, which is incorporated by reference herein in its entirety and for all purposes.)

[0061] “Metal polar,” as used herein, is the (0001) plane, also known as the c-plane.

[0062] “Nitrogen or N polar,” as used herein refers to the -c-plane or (000 1 “ ) surface (see Caroline E. Reilly et al., Metalorganic chemical vapor deposition of InN quantum dots and nanostructures, Light: Science & Applications (2021) 10:150, and see C. Kittel, Introduction to Solid State Physics, 8thEdition, John Wiley & Sons, 2005, pp.l 1-13).

[0063] “Quantum well structure,” as used herein, refers to a structure having a material sandwiched between two layers of materials with a wider bandgap.

[0064] "AIN templates," as used herein, refers to AIN films grown on low-cost substrates (see, for example, Kenjiro Uesugi and Hideto Miyake, Fabrication of AIN templates by high-temperature face-to-face annealing for deep UV LEDs, 2021 Jpn. J. Appl. Phys. 60 120502).

[0065] For ternary alloys, of type AxX|.xN, used in the quantum well structure of these teachings, x in each ternary alloy is chosen so that a middle material is sandwiched between two layers of materials with a wider bandgap than a bandgap of the middle material.

[0066] Designs, for metal polar materials, which incorporate n-type compensation n-doping in the strained QW to counter the negative polarization effect at the (AlxGroupIII(iX))N / Group IIIN interface and reduce the internal electric field in the well are presented. Designs for Nitrogen polar materials, which incorporate p-doping to compensate for the 2DEG at the bottom interface, are also presented.

[0067] In one instantiation, the semiconductor quantum well structure of these teachings includes a metal polar first layer; a material of the metal polar first layer including one of AIN, AlxGaixN, AlxIni-xN, AlxScixN, AlxBixN, AlxYi-xN, or AlxLaixN, a metal polar second layer of Group IIIN material epitaxially deposited on the metal polar first layer, at least one the metal polar first layer or the metal polar second layer having an n-doped section, and, a metal polar third layer epitaxially deposited on the metal polar second layer of Group IIIN material, a material of the metal polar third layer including one of AIN, AlxGarxN, AlxInrxN, AlxScixN, AlxBrxN, AlxYrxN, or AlxI.;i|XN. A thickness of the metal polar first layer and the material of the metal polar first layer and a thickness of the second metal polar layer of Group IIIN material are selected such that, in absence of the n-doped section, at the interface between the metal polar first layer and the second metal polarDocket No.: 11208-02layer of Group IIIN material, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A thickness of the third metal polar layer and the material of the third metal polar layer and the thickness of the second metal polar layer of Group IIIN material are selected such that, at an interface between the second metal polar layer of group III material and the third metal polar layer, a net positive polarization charge induces a 2D electron gas (2DEG). A density of the n-doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form the interface between the metal polar first layer and the second metal polar layer of Group IIIN material.

[0068] In one instantiation, the method of these teachings for fabricating a semiconductor quantum well structure includes epitaxially depositing a metal polar-first layer on a substrate, a material of the metal polar first layer including one of AIN, AlxGai-xN, AlxIm.xN, AlxSci.xN, AlxBi-XN, AlxYi.xN, or AlxLarxN, epitaxially depositing a metal polar second layer of Group IIIN material on the metal polar first layer, n-doping one of a section of the material of the metal polar first layer or a section of the material of the metal polar second layer, epitaxially depositing a metal polar third layer on the metal polar second layer of Group IIIN material. A material of the metal polar third layer comprising one of AIN, AlxGaixN, AlxInixN, AlxScrxN, AlxBrxN, A1XY].XN, or AlxLaixN. A thickness of the metal polar first layer and the material of the metal polar-first layer and a thickness of the second metal polar layer of Group IIIN material are selected such that, in absence of the n-doped section, at the interface between the metal polar first layer and the second metal polar layer of Group IIIN material, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A thickness of the third metal polar layer and the material of the third metal polar layer and the thickness of the second metal polar layer of Group IIIN material are selected such that, at an interface between the second metal polar layer of group III material and the third metal polar layer, a net positive polarization charge induces a 2D electron gas (2DEG). A surface density of the n-Delta doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form the interface between the metal polar first layer and the second metal polar layer of Group IIIN material.

[0069] Figure 1 shows an instantiation of the quantum well structure of these teachings. Referring to Figure 1, in the instantiation shown therein, a metal polar second layer of Group III N material, GaN in the instance shown, is epitaxially deposited over a metal polar first layer, AIN in the instance shown, and a metal polar third layer, AIN in the instance shown, is epitaxially deposited over the metal polar second layer. The GaN layer, over a region in the GaN layer, is n-doped.

[0070] It should be noted that n-doping, as used herein, includes n-doping a region or layer, n-doping a region or layer with non-uniform dopant concentration, or n-6-doping.Docket No.: 11208-02

[0071] In order to further elucidate these teachings, results for an illustrative instantiation of the quantum well structure having AlN / GaN / AlN, with metal polar layers and n-8-doping of the metal polar second layer (GaN), arc presented herein below. It should be noted that these teachings arc not limited only to the illustrative instantiation.

[0072] Undoped and 8-doped QW HEMT heterostructures, as depicted in Figs. 1 A and IB, are epitaxially grown on Al-polar single-crystal AIN substrates. The thickness of all layers is maintained identical in both samples to focus on the impact of 8-doping. The numerically-calculated energy band diagram of the undoped QW HEMT in Fig. 1C illustrates high electric field in the QW due to the large polarization effect. At the top AlN / GaN interface, the net positive polarization charges induce 2DEG, while at the bottom GaN / AlN interface, the net negative polarization charges induce 2DHG. Both 2DEG and 2DHG are confined in the QW. Introducing 8-doping (sj = 5 x 1013cm-2) of a section of the second GaN layer at the bottom GaN / AlN interface suppresses 2DHG and moves the valence band farther away from the Fermi level, as shown in Fig. ID. This leads to a flattened energy band and a reduction of the internal electric field, which shifts the 2DEG centroid away from the interface, decreasing the strength of IR (interface roughness) scattering, and consequently enhancing electron mobility. The 8-doped QW HEMT exhibits a 2DEG density of 3.24xl013cm-2with electron mobility of 854.6 cm2 / Vs at RT and 2240.2 cm2 / Vs at 10 K, resulting in a RT sheet resistance of 226.7 Q / n. In contrast, the un-doped QW HEMT exhibits a higher RT sheet resistance of 501.9 £! / □ (with electron mobility of 611.1 cm2 / Vs and 2DEG density of 2.04 x 1013cm-2at RT).

[0073] Simulated carrier densities of the undoped and 8-doped QW HEMTs are shown in Figures IE and IF, respectively. High-density 2DEG is confined to the AlN / GaN interface. The addition of silicon donors in the 8-doped QW HEMT eliminates the presence of 2DHG at the bottom interface. The insets in Figures 1E-1F show the energy of the electronic sub-bands and the moduli squared of the selected electron wavefunction for the undoped and 8-doped QW HEMTs, respectively.

[0074] 8-doping has been previously applied in n-type doping in N-polar GaN HEMTs, where it mitigates the modulation of donor traps if there are defects at the negatively charged interface during device operation. 8-doping density, in the present teachings, was selected by calculation from a self-consistent Schrodinger-Poisson calculator, assuming full ionization. In the undoped QW HEMTs, the calculated 2DHG density at the bottom interface is ps= 3.91 x 1013cm-2.8-doping is applied after 1 nm of GaN QW. Introducing 8-doping with a density of sg= 4 x 1013cm-2reduces the 2DHG density to ps= 5.59 x 1011cm-2. Further increasing the doping density to Sa = 5 x 1013cm-2completely shifts the valence band below the Fermi level, resulting in a flattened energyDocket No.: 11208-02band, eliminating the 2DHG at the bottom interface. However, an increase in doping density to s« = 6 x 1013cm-2leads to an additional electron channel at the bottom interface. Therefore, in one instance, a 8-doping density of Sa = 5 x 1013cm-2is chosen to incoiporate into QW HEMTs, aiming to counterbalance the presence of the 2DHG and reduce the internal electric field in the well.

[0075] Figure 1H shows an instance of the instantiation of the quantum well structure of these teachings shown in Fig. 1G, in which the Group IIIN material is one of GaN or InN (GaN in the instance shown), and in which the metal polar third layer has an AIN interlayer epitaxially deposited on the metal polar second layer of Group IIIN material and a metal polar sub-layer epitaxially deposited on the AIN interlayer, the metal polar sub-layer comprising one of AlxGaixN, AlxIni.xN, AlxScj.xN, AlxBi-xN, AlxYi-xN, or AlxLaixN. Similar instantiations, for the instantiation of the quantum well structure of these teachings shown in Fig. 1, are within the scope of these teachings.

[0076] A flowchart representation of an instantiation of the method of these teachings is shown in Figure 5. Referring to Figure 5, in the instantiation shown therein, a metal polar first layer is epitaxially deposited on a substrate (step 210, Figure 5). A material of the metal polar first layer comprising one of AIN, AlxGaixN, AlxIni-xN, AlxSci-xN, AlxBj.xN, A1XY|.XN, or AlxLaixN. A metal polar-second layer of Group IIIN material is epitaxially deposited on the metal polar first layer (step 220, Figure 5). One of a section of the material of the metal polar first layer or a section of the metal polar second layer is n-doped (step 230, Fig. 5). A metal polar third layer is epitaxially deposited on the metal polar second layer of Group IIIN material (Step 250, Fig. 5). A material of the metal polar third layer includes one of AIN, AlGaN, AllnN, AlScN, A1BN, A1YN, or AlLaN.

[0077] A flowchart representation of an instantiation of the method of these teachings in which n-doping is n-6-doping is shown in Figure 5A. In that instantiation, epitaxially depositing the metal polar second layer of Group IIIN material on the metal polar first layer comprises epitaxially depositing a pre-determined portion of the metal polar second layer of Group IIIN material on the metal polar first layer, n-8-doping one of a section of the material of the metal polar first layer or a section of the material of the pre-determined portion of a metal polar second layer at an interface between the metal polar first layer and the metal polar second layer of Group IIIN material, and epitaxially depositing a remainder portion of the metal polar second layer of Group IIIN material on the pre-determined portion of the metal polar second layer of Group IIIN material.

[0078] Referring to Figure 5A, in the instantiation shown therein, a metal polar first layer is epitaxially deposited on a substrate (step 210, Figure 5A). (Steps that are the same as those in Figure 5 have the same number.) A pre-determined portion of a metal polar second layer of Group IIIN material is epitaxially deposited on the metal polar first layer (step 225, Figure 5A). One of a section of the material of the metal polar first layer or a section of the metal polar second layer is n-8- dopedDocket No.: 11208-02at an interface between the metal polar first layer and the metal polar second layer of Group IIIN material ( step 235, Figure 5A). A remainder portion of the metal polar second layer of Group IIIN material is epitaxially deposited on the pre-determined portion of the metal polar second layer (step 240, Figure 5A). A metal polar third layer is epitaxially deposited on the metal polar second layer of Group IIIN material (Step 250, Fig. 5A).

[0079] Veeco GEN10 molecular beam epitaxy (MBE) was used to grow the heterostructures shown in Fig. 1A. The single-crystal AIN substrates, with dislocation densities < 104cm—2, were from Crystal IS. Prior to epitaxial growth, the substrates underwent essential cleaning steps (see K. Lee, Y. Cho, L. J. Schowalter, M. Toita, H. G. Xing, and Jena, “Surface control and MBE growth diagram for homoepitaxy on single-crystal AIN substrates,” Applied Physics Letters 116 (2020), which is incorporated by reference herein in its entirety and for all purposes). After ex situ cleaning in solvents and acids, diced AIN substrates were loaded into the MBE system and outgassed at 200 °C for 7 h. Subsequently, in situ Al-assisted surface cleaning was employed, which involves repeated cycles of aluminum adsorption and desorption to remove the native surface oxide and enable high-quality homoepitaxy.

[0080] After Al-assisted surface cleaning, a 500 nm AIN buffer layer was homoepitaxially grown under metal-rich growth conditions to ensure step-flow growth mode for high crystallinity. The active region following the sequence of 20 nm GaN QW, 6 nm AIN barrier, and 1 nm GaN cap were grown under metal-rich conditions and without any growth interruption. The substrate temperature for the active region of undoped QW HEMTs was maintained at a thermocouple temperature (Te) of 850 °C, while for 6-doped QW HEMTs, the substrate temperature was adjusted to Te= 820 °C to ensure the presence of Ga droplets on the surface during the 8-doping process. Silicon 8-doping was incorporated after deposition of 1 nm GaN QW. During 8-doping, silicon shutter was open while Ga shutter was closed, allowing a sheet of silicon donors with density s» = 5 x 1013cm—2to be incorporated. Once the 8-doping process was completed, Ga shutter promptly opened to resume the growth of the remaining 19 nm GaN QW. The 8-doping time was calibrated using a separate MBE grown silicon-doped GaN at silicon cell temperature of Tsi = 1195 °C, yielding doping density of 1.23 x 1019cm-3. After the epitaxial growth, the substrates were immediately cooled down to RT, and excess Ga droplets were removed ex situ using HC1.

[0081] The structural quality of the heterostructures was assessed through high-resolution X-ray diffraction (HRXRD) with a Panalytical Empyrean® diffractometer emitting Cu Kai radiation (1.54 A). Fig. 2A shows the diffraction patterns of both samples measured around the (002) symmetric reflection. The dashed red lines in Fig. 2A represent the theoretical diffraction patterns calculated using a dynamical diffraction model. Clearly resolved interference fringes suggestDocket No.: 11208-02atomically sharp hetero-interfaces. The thicknesses of each layers were extracted from the good agreement between the measured and simulated result, showing precise control over thicknesses. The rcc around the asymmetric (-105) diffraction in Figs. 2B and 2C show coherently strained layers throughout the whole device structure. This implies that silicon incorporation has no measurable impact on the strain state of the film. The surface morphologies of the samples were measured using atomic force microscopy (AFM) with an Asylum Research Cypher ES setup. The AFM scans of both samples, as shown in Figs. 2D and 2E reveal atomic steps, indicative of step flow growth mode throughout the whole epitaxial process. Additionally, the sub-nanometer root-mean-square (rms) roughness validates their smooth surface morphologies.

[0082] Temperature-dependent Hall-effect measurements were conducted using a Van der Pauw geometry with soldered indium dots as Ohmic contacts. The carrier concentration ns, mobility p . and sheet resistance Rs — at 290 K and 10 K — are summarized in Table I and Figs. 3A-3C. Fig. 3A shows that the temperature-independent 2DEG density remains unchanged down to cryogenic temperature, confirming their polarization-induced origin. Introducing silicon 6-doping enhances the 2DEG density from 2.04 x 1013cm-2in the undoped case to 3.24 x 1013cm-2. The increase of the 2DEG density is associated with a lowering of the internal electric field in the well. This leads to a decrease in sub-band energies and enables a larger electronic population within the well. The calculated energy band diagram and the energy of the electronic subbands, presented in the inset of Fig. 2E, show a single subband positioned at 0.266 eV below the Fermi level in the undoped QW HEMT. In contrast, 8-doped QW HEMT exhibits lower internal electric field, leading to two subbands populating electrons within the well, as shown in the inset of Fig. IF. The second subband, situated 0.056 eV below Fermi level, is relatively shallow, with the majority of electrons at this AlN / GaN heterojunction occupying the first subband, positioned 0.33 eV below Fermi level. The measured 2DEG densities are close to the calculated density from a self-consistent Schrodinger-Poisson solver with a surface barrier height of 0.5 eV.TABLE I. 2DEG densities (ns), mobilities (p) and sheet resistance (Rs) measured via Halleffect at 290 K and 10 K and calculated internal electric field (Favg) for the undoped and 8-doped QW HEMTs, respectively.QW 290 K Rs 290 K 10 K plO K Rs 10 K Favg HEMTs nsns(cm2 / Vs) (MV / cm) (1013p290 K (Q / n) (1013(Q / n)cm-2) (cm2 / V s) cm-2)Undoped 2.04 611.1 501.9 2.01 1211.5 255.9 3.808-doped 3.24 854.6 226.7 3.21 2240.2 86.86 2.84Docket No.: 11208-02

[0083] To elucidate the physical origin behind the improved electron mobility in 8-doped QW HEMT, temperature-dependent Hall-effect measurements combined with a transport model are employed to identify the limiting scattering mechanisms, as shown in Fig. 3B. The effect of Coulomb scattering due to dislocations and remote ionized impurities scattering, was found to be negligible compared to those shown in the figure. The electron effective mass m* used in the theoretical calculation for both the undoped QW HEMT and 8-doped QW HEMT is m* = 0.25 mo, where mo is the free electron mass. The high electron effective mass compared to conventional AlGaN / GaN heterostructures with m* ~ 0.22 mo might arise from the compressive strain of the GaN channel and the nonparabolicity of the electronic subband. The impact of 8-doping on the transport properties of QW HEMTs is disclosed below.

[0084] IR (interface roughness) scattering is the primary mobility-limiting factor in the undoped QW HEMTs. In Fig. 3B, it is seen that the POP ( Polar Optical Phonon) scattering is similar for both samples, with the main difference at all temperatures attributed to IR scattering. The modeling of IR (interface roughness) scattering involved using a correlation length A of 1.25 nm and a roughness parameter 6 of 0.27 nm for the undoped QW HEMT and 0.36 nm for the 8-doped QW HEMT. These roughness parameter are of the same order of magnitude as the experimentally measured rms roughness. The IR scattering rate has a strong dependence on the internal electric field and screening factor. The weighted average electric field Faig>at the electron wavefunction location, is calculated. The introduction of 8-doping results in a decrease in F,„ ., from 3.80 MV / cm in the undoped QW HEMT) to 2.84 MV / cm in the 6-doped QW HEMT. This 25% lower in Favgrelocates the 2DEG centroid away from the interface, decreasing the intensity of IR scattering. Moreover, the increased 2DEG density in 8-doped QW HEMT enhances the screening of the scattering potential. These combined effects significantly reduce IR scattering, resulting in an enhancement in electron mobility. Particularly noteworthy is the nearly two times increase in low-temperature electron mobility from 1211.5 to 2240.2 cm2 / Vs, which is attributed to the reduction in IR scattering. Thanks to the increase in both the 2DEG density and mobility, 8-doped QW HEMT demonstrates an over 50% reduction in sheet resistance, achieving RT sheet resistance of 226.7 Q / n, as illustrated in Fig.3C.

[0085] Figure 4 benchmarks the 2DEG density and RT (room temperature) mobility of 8-doped QW HEMT against other previously reported AlN / GaN / AlN heterostructures. The RT mobilities of undoped heterostructures were limited to 620 cm2 / Vs, as indicated by the black triangles in Fig. 4. To address this limitation, initial enhancements were made by relaxing the GaN channel, resulting in RT electron mobility > 1000 cm2 / Vs and RT sheet resistance < 300 Q / n. But issues such as strain relief mediated by dislocation formation have been shown to cause increased dispersion andDocket No.: 11208-02higher gate leakage currents in HEMTs. Additionally, the high dislocation density in GaN enhances phonon-dislocation scattering, consequently decreasing its thermal conductivity. In these teachings, 8-doped XHEMTs are seen to attain the highest RT mobility of 854.6 cm2 / Vs and lowest RT sheet resistance of 226.7 £! / □ among all coherently str ained AlN / GaN / AlN heterostructures reported to date, without paying the penalty of relaxing the GaN channel and maintaining single-crystal properties throughout the heteros tincture.

[0086] Figure 4A shows a high-electron-mobility transistor (HEMT) including an instantiation of the quantum well structure of these teachings in which a section of the second layer, GaN layer, is n-8-doped at the interface between the first layer, AIN buffer, and the metal polar second layer, GaN layer. Although in the instantiation shown in Fig. 4A, n-doping is n-6-doping, other n-doping, as disclosed herein, can also be used. The quantum well structure of the metal polar instantiation disclosed above can be incorporated into a HEMT taking advantage of the increased mobility available to those instantiations. Figures 4A and 4C show illustrative instantiations. The scope of these teachings is not limited only to those illustrative instantiations. In the illustrative instantiations, the Group IIIN material is GaN, material of a first metal polar layer is AIN, and the material of the metal polar third layer is AIN. Referring to Figure 4A, in the instantiation shown therein, a cap layer, GaN in the instantiation shown, is deposited on the metal polar third layer, AIN in the instantiation shown. The cap layer can also be a layer of another Group IIIN material. Although the instantiation shown is a metal polar instantiation, a nitrogen polar instantiation of a HEMT can have a cap layer of Group IIIN material deposited over the nitrogen polar third layer of the quantum well heterostructure.

[0087] The introduction of silicon 6-doping improves electron mobility in AlN-based GaN QW HEMTs without resorting to relaxed GaN channel. The 6-doped QW HEMT, grown on a singlecrystal AIN substrate, exhibits a smooth surface morphology, sharp hetero-interfaces, and coherently strained GaN QW layer. The incorporation of 8-doping compensates the negative polarization effect and reduces the internal electric field in the well. This contributes to a high RT mobility of 854.6 cm2 / Vs and a high 2DEG density of 3.24 x 1013cm-2, resulting in a RT sheet resistance of 226.7 Q / n. This marks among the highest RT mobility and lowest sheet resistance achieved to date in coherent, un-relaxed AlN / GaN / AlN HEMTs, rendering them highly effective for RF and power electronics on the AIN platform.

[0088] For the metal polar quantum well structure illustrative instantiations shown above, in one instance, the Group IIIN material is gallium nitride, the material of the metal polar-first layer is AIN, and the material of the metal polar third layer is AIN. For that illustrative instantiation, the n-6-doping density is between about 4.75 x 1013cm-2to 5.25 x 1013cm-2. For that illustrativeDocket No.: 11208-02instantiation, the semiconductor quantum well structure exhibits a mobility greater than 800 cm2 / V s at room temperature (290° K).

[0089] In other instances of the metal polar quantum well structure instantiation, the Group IIIN material is InN. In further instances, the Group IIIN material is one of (GaxI .x)N, (AlxGai-x)N, or (AlxIni-x)N. In still other instances, the material of the metal polar third layer is one of AlxGaixN, AlxSc].xN, AlxYuxN, or AlxLaixN. In some of those still other instances, the Group IIIN material is GaN.

[0090] Figure 1G shows another instantiation of the quantum well structure of these teachings. Referring to Figure 1G, in the instantiation shown therein, a metal polar second layer of Group III N material ,GaN in the instance shown, is epitaxially deposited over a metal polar first layer, AIN in the instance shown, and a metal polar third layer, AIN in the instance shown, is epitaxially deposited over the metal polar second layer. The metal polar first layer, AIN, over a region in the metal polar first layer, is n-doped.

[0091] In one instance, in the instantiation of the quantum well structure of these teachings shown in Fig. 1G, n-doping is n-6-doping. That instance is shown in Figure 4B. Figure 4B shows another instantiation of the quantum well structure of these teachings in which doping is 6-doping and in which a section of the material of the metal polar first layer, AIN first layer, is n-6-doped at the interface between the first layer, AIN layer, and the metal polar second layer, GaN layer.

[0092] Figure 4C shows another high-electron-mobility transistor (HEMT) including the instantiation of the quantum well structure of these teachings shown in Fig. 4B. Another instantiation of a fabricated silicon 5-doped AIN XHEMT (hereafter referred to as an AIN XHEMT) is shown schematically in Figure 4D. The device was passivated with a 106-nm-thick near-stoichiometric silicon nitride (SiNx) layer deposited by low-pressure chemical vapor deposition (LPCVD). A nickel / gold metal stack was used to form the Schottky gate contact, and a source-connected field plate (SCFP) was implemented, separated from the gate metal by a 118 nm thick silicon nitride layer deposited, in one instance, by plasma-enhanced chemical vapor deposition (PECVD).

[0093] Following device fabrication, the contact resistance (J?c) and sheet resistance (7?sh) were extracted using the linear transfer length method (TLM), as shown in Figure 4E. An average Rcof 0.39 ± 0.04 Q mm and RSh of 276 ± 9.5 Q / n were obtained from multiple TLM measurements across the sample. The extracted / G, closely aligns with the RSh of 283 Q / o obtained by the Hall effect measurement on an on-wafer van der Pauw pattern post-device fabrication. The lower / G. compared to the value measured on the as-grown sample prior to device fabrication, is attributed to the increased 2DEG density due to surface passivation with LPCVD SiNx.Docket No.: 11208-02

[0094] Figure 4F shows the representative output characteristics of AIN XHEMTs with the nominally same dimensions with the device in Figure 4D. At room temperature, the device exhibits a maximum drain current density exceeding 2 A / mm at a gate voltage of 2 V. This drain current density is realized without aggressive lateral scaling of the device, owing to the enhanced 2DEG density provided by the AIN barrier and silicon 4-doping. Figure 4G shows the transfer characteristics of the AIN XHEMTs. At a fixed drain voltage of 10 V, a threshold voltage of -4.2 V and a peak extrinsic transconductance exceeding 0.4 S / mm were extracted. Figure 4H shows the small-signal unilateral gain (LT), current gain (Ifeil2), maximum stable gain (MSG), and maximum available gain (MAG), which were extracted from the measured S-parameters of a device biased at a gate voltage of -2.8 V and a drain voltage of 10 V. The extra parasitic delays introduced by device probe pads were not deembedded. The cut-off frequency ( r) and maximum oscillation frequency ( inax) of 21 and 40 GHz, respectively, were extracted from I / / 2112and U, both of which exhibited the expected -20 dB / dec slope.

[0095] Pulsed current-voltage ( / D - VDS) measurements were applied to the AIN XHEMTs using 500 nm long pulses at a 1 ms period to investigate their dynamic behavior under large-signal drive conditions. Improvement in trapping phenomena was achieved in XHEMTs with silicon d'-doping. The AIN XHEMTs demonstrated negligible current collapse under the same stress bias condition of Vcsq, Vosq= -5 V, 20 V, as shown in Figure 41. (Cold bias condition (VGSq / VDSq = 0 V / 0 V) was used as a reference, and the applied stress bias conditions were VGSq / VDSq = -5V / 0V, -5V / 10V, and -5V / 20V.) In the case of AIN XHEMTs, silicon 8-doping shifts the Fermi level closer to the midgap, effectively filling the valence band states. As a result, the capture of electrons is Pauli-blocked, as shown in the off-state energy band diagram of AIN XHEMTs in Figure 1C, preventing partial depletion of 2DEG.

[0096] The CW large-signal measurements performed on AIN XHEMTs further confirmed the effectiveness of silicon 8-doping in suppressing RF dispersion. Biased at VDSq = 17 V and IDSq = 0.26 A / mm, AIN XHEMTs exhibited a maximum Pout of 5.92 W / mm and a peak PAE of 65%, as shown in Figure 4J when tuned for maximum PAE; under the same matching conditions, the associated Poutat the peak PAE was 4.2 W / mm. These results, enabled by silicon 8-doping, represent nearly 6-fold and 3-fold increases in Pout and PAE, respectively, compared to the undoped QW HEMTs. Further increase in Poutis currently limited by the device breakdown voltage due to a non-optimized electric field management near the gate edge.

[0097] To evaluate the potential of AIN XHEMTs, we benchmark the large signal RF performance obtained on the XHEMTs of these teachings, grown on Al-polar AIN, were benchmark against their counterpart: metal-polar, single-channel GaN HEMTs reported in the literature. FigureDocket No.: 11208-024K benchmarks the large-signal performance of silicon 5-doped AIN XHEMTs in terms of Pout as a function of GaN channel thickness (GaN thickness between the top and the bottom barrier). As the GaN channel thickness decreases, large-signal RF amplification becomes increasingly challenging due to factors such as mobility degradation and higher DC-RF dispersion. By incorporating silicon 8-doping into the AIN XHEMT structure to overcome these challenges, these teachings report the first large-signal operation of double-heterostructure HEMTs with a channel thickness at or below 20 nm. Moreover, the reported Pout is the highest achieved for Vosqat or below 20 V among all metal-polar, single-channel GaN HEMTs, though not all available data in the literature are at 10 GHz.

[0098] In Figure 4L, Poutof metal-polar, single-channel GaN HEMTs, including but not limited to double-heterostructure HEMTs, is plotted against Vosq in the frequency range from 8 to 12 GHz. At a given Vosq, AIN XHEMTs deliver significantly larger Poutcompared to conventional AlGaN / GaN HEMTs, owing to their higher 2DEG density. Lastly, Figure 4M shows the associated Poutat peak PAE of AIN XHEMTs compared with those of GaN HEMTs in Figure 4L, measured at at or under 35 V in the X-band. ( The color map shows the dissipated power (Pdiss) at a given Pout and PAE, derived under the assumption of 8 dB transducer power gain at peak PAE.) An improvement in the large-signal RF performance of AIN XHEMTs is highlighted here, compared to the undoped QW HEMT. When the problem of charge trapping, thus RF dispersion, is addressed in the AIN XHEMT, the HEMT performance on the AIN platform moves closer to the upper-right desired corner which is for simultaneously higher Poutand PAE with a cooler device junction.

[0099] In some instances of the method for fabricating metal polar semiconductor quantum well structure, epitaxially depositing is performed by molecular beam epitaxy (MBE). In other instances, epitaxially depositing is performed by one of Metalorganic vapour-phase epitaxy (MOCVD), Hydride vapour-phase epitaxy (HVPE), or Reactive Sputtering. In some instances, the dopant used in n-doping is Si. In other instances, the dopant used in n- doping is Ge. The method for fabricating metal polar semiconductor quantum well structure of these teachings can be used for fabricating any instantiation of the metal polar semiconductor quantum well structure, including the ones disclosed above. In one instance, the substrate comprises one of single crystal AIN, Si, SiC, AIN template, or Sapphire.

[0100] In another instantiation, the semiconductor quantum well structure of these teachings includes a nitrogen polar first layer, a material of the nitrogen polar first layer including one of AIN, AlxGai xN, AlxIni xN, AlxSci-xN, AlxBi xN, AlxYi_xN, or AlxLai-xN, a second nitrogen polar layer of Group IIIN material epitaxially deposited on the nitrogen polar first layer, at least one of the nitrogen polar first layer or the second nitrogen polar layer being p-doped, and, a nitrogen polar-third layer epitaxially deposited on the second nitrogen polar layer, a material of the nitrogen polar third layerDocket No.: 11208-02including one of AIN, AlxGai.xN, AlJni xN, AlxSci.xN, A1XB|XN, A1XY|XN, or AlxLarxN. A thickness of the nitrogen polar first layer and the material of the nitrogen polar first layer and a thickness of the second nitrogen polar layer of Group IIIN material are selected such that, in absence of p-doping, at the interface between the nitrogen polar first layer and the second nitrogen polar-layer of Group IIIN material, net positive polarization charge is sufficient to induce a 2D electron gas (2DEG). A thickness of the third nitrogen polar layer and the material of the third nitrogen polar layer and the thickness of the second nitrogen polar layer of Group IIIN material are selected such that, at an interface between the second nitrogen polar layer of group III material and the third nitrogen polar layer, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A density of the p-doping is selected such that the 2DEG is suppressed. In order to elucidate these teachings an illustrative instantiation is presented herein below. These teachings are not limited to only that illustrative instantiation.

[0101] Figures 6A and 6B show the difference in the polarization charge distribution in metal polar structures compared to that in nitrogen polar-structures. In the metal polar structure, shown in Figure 6A, at the top AlN / GaN interface, the net positive polarization charges induce 2DEG, while at the bottom GaN / AlN interface, the net negative polarization charges induce 2DHG. In the nitrogen polar structure, shown in figure 6B, at the top AlN / GaN interface, the net negative polarization charges induce 2DHG. while at the bottom GaN / AlN interface, the net positive polarization charges induce 2DEG.

[0102] Figure 7 shows a schematic of a nitrogen polar instantiation of the quantum well structure of these teachings. Referring to Figure 7, in the instantiation shown therein, the quantum well structure shown therein has a p-doped nitrogen polar AIN first layer, a nitrogen polar second layer of group III N material, GAN, epitaxially deposited on the nitrogen polar first layer and a nitrogen polar third layer, AIN, epitaxially deposited on the nitrogen polar second layer.

[0103] Figure 7A shows a schematic of another nitrogen polar instantiation of the quantum well structure of these teachings described above. Referring to Figure 7A, in the instantiation shown therein, the quantum well structure shown therein has a nitrogen polar AIN first layer, a p-doped nitrogen polar second layer of group III N material, GAN, epitaxially deposited on the nitrogen polar first layer and a nitrogen polar third layer, AIN, epitaxially deposited on the nitrogen polar second layer. The dopant concentration in the p-doped region does not have to be uniform. It could increase in the vicinity of the interface between the nitrogen polar first layer and the nitrogen polar-second layer.

[0104] A thickness of the nitrogen polar first layer and the material of the nitrogen polar first layer and a thickness of the nitrogen polar second layer of Group IIIN material are selected such that,Docket No.: 11208-02in absence of p-doping, at the interface between the nitrogen polar first layer and the second nitrogen polar layer of Group IIIN material, net positive polarization charge is sufficient to induce a 2D electron gas (2DEG). A thickness of the nitrogen polar third layer and the material of the nitrogen polar third layer and the thickness of the second nitrogen polar layer of Group IIIN material are selected such that, at an interface between the second nitrogen polar layer of group III material and the nitrogen polar third layer, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A density of the p-doping is selected such that the 2DEG is suppressed. The p-type compensation doping eliminates or reduces parallel conduction.

[0105] For the nitrogen polar quantum well structure illustrative instantiations shown above, in one instance, the Group IIIN material is gallium nitride, the material of the metal polar first layer is AIN, and the material of the metal polar third layer is AIN.

[0106] For the nitrogen polar quantum well structure disclosed above, in other instances, the Group IIIN material is InN. In further instances, the Group IIIN material is one of (GaxInrx)N, (AlxGai-x)N, or (AlxIni-x)N. In still other instances, the material of the metal polar third layer is one of AlxGai-xN, AlxSci xN, A1XY]_XN, or AlxLaixN. In some of those still other instances, the Group IIIN material is GaN.

[0107] In another instantiation, the method of these teachings for fabricating a semiconductor quantum well structure includes epitaxially depositing a nitrogen polar first layer on a substrate; a material of the nitrogen polar first layer includes one of AIN, AlxGai-xN, AlxIni-xN, AlxSci xN, AlxBi xN, AlxYi-xN, or AlxLai-xN, epitaxially depositing a second nitrogen polar-layer of Group IIIN material on the nitrogen polar fust layer, at least one the nitrogen polar first layer or the second nitrogen polar layer being a p-doped layer, and epitaxially depositing a third nitrogen polar layer on the second nitrogen polar layer, a material of the third nitrogen polar layer comprising one of AIN, AlxGaj xN, AlxIni-xN, AlxScrxN, AlxBixN, A1XY ixN, or AlxLaixN. A thickness of the nitrogen polar first layer and the material of the nitrogen polar first layer and a thickness of the second nitrogen polar-layer of Group IIIN material are selected such that, in absence of p-doping, at the interface between the nitrogen polar first layer and the second nitrogen polar-layer of Group IIIN material, net positive polarization charge is sufficient to induce a 2D electron gas (2DEG). A thickness of the third nitrogen polar layer and the material of the third nitrogen polar layer and the thickness of the second nitrogen polar layer of Group IIIN material are selected such that, at an interface between the second nitrogen polar layer of group III material and the third nitrogen polar layer, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A density of the p-doping is selected such that the 2DEG is suppressed.Docket No.: 11208-02

[0108] A flowchart representation of one instantiation of the method of these teachings is shown in Figure 8. Referring to Figure 8, in the instantiation shown therein, a p-doped nitrogen polar first layer is epitaxially deposited on a substrate (step 410, Fig. 8). A material of the nitrogen polar first layer includes one of AlxGarxN, AlxIn]_xN, AlxSci-xN, AlxBi-xN, AlxYi-xN, or AlxLai-xN. A second nitrogen polar layer of Group IIIN material is epitaxially deposited on the p-doped nitrogen polar first layer (step 420, Fig. 8). A third nitrogen polar layer is epitaxially deposited on the second nitrogen polar layer (step 430, Fig. 8). a thickness of the nitrogen polar first layer and the material of the nitrogen polar first layer and a thickness of the second nitrogen polar layer of Group IIIN material are selected such that, in absence of p-doping, at the interface between the nitrogen polar first layer and the second nitrogen polar layer of Group IIIN material, net positive polarization charge is sufficient to induce a 2D electron gas (2DEG). A thickness of the third nitrogen polar layer and the material of the third nitrogen polar layer and the thickness of the second nitrogen polar layer of Group IIIN material are selected such that, at an interface between the second nitrogen polar layer of group III material and the third nitrogen polar layer, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A density of the p-doping is selected such that the 2DEG is suppressed.

[0109] A flowchart representation of another instantiation of the method of these teachings is shown in Figure 8A. Referring to Figure 8A, in the instantiation shown therein, a nitrogen polar first layer is epitaxially deposited on a substrate (step 415, Fig. 8A). A material of the nitrogen polar first layer includes one of AlxGaixN, AlxIni-xN, AlxScixN, AlxBixN, AlxYi-xN, or AlxLai-xN. A p-doped second nitrogen polar-layer of Group IIIN material is epitaxially deposited on the p-doped nitrogen polar first layer (step 425, Fig. 8A). A third nitrogen polar-layer is epitaxially deposited on the second nitrogen polar layer (step 435, Fig. 8A). A thickness of the nitrogen polar-first layer and the material of the nitrogen polar first layer and a thickness of the second nitrogen polar layer of Group IIIN material are selected such that, in absence of p-doping, at the interface between the nitrogen polar first layer and the second nitrogen polar layer of Group IIIN material, net positive polarization charge is sufficient to induce a 2D electron gas (2DEG). A thickness of the third nitrogen polar-layer and the material of the third nitrogen polar layer and the thickness of the second nitrogen polar layer of Group IIIN material are selected such that, at an interface between the second nitrogen polar layer of group III material and the third nitrogen polar layer, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A density of the p-doping is selected such that the 2DEG is suppressed.

[0110] In some instances of the method for fabricating nitrogen polar-semiconductor quantum well structures as disclosed above, epitaxial deposition is performed by molecular beam epitaxy (MBE). In other instances, epitaxially depositing is performed by one of MetalorganicDocket No.: 11208-02vapour-phase epitaxy (MOCVD), Hydride vapour-phase epitaxy (HVPE), or Reactive Sputtering. In some instances, the dopant used in p-doping is Mg (Magnesium) or B (boron). In one instance, the substrate comprises one of single crystal AIN, Si, SiC, AIN template, or Sapphire.

[0111] The method for fabricating nitrogen polar semiconductor quantum well structure of these teachings can be used for fabricating any instantiation of the nitrogen polar semiconductor quantum well structure as generally described above, including the specific ones disclosed above.

[0112] In yet another instantiation, the semiconductor quantum well structure of these teachings includes a nitrogen polar first layer, a material of the nitrogen polar first layer includes one of AIN, AlxGai xN, AlxInrxN, AlxSci.xN, AlxBi-xN, AlxYi_xN, or AlxLai.xN, a nitrogen polar second layer of Group IIIN material epitaxially deposited on the nitrogen polar first layer, and, a nitrogen polar third layer epitaxially deposited on the second nitrogen polar-layer, a material of the third nitrogen polar layer comprising one of AIN, AlxGaixN, AlxInixN, AlxSci.xN, AlxBjxN, AlxYi.xN, or AlxLai xN. At least one of the nitrogen polar third layer or the nitrogen polar-second layer comprises an n-doped section at an interface between nitrogen polar third layer and the nitrogen polar second layer of Group IIIN material. A thickness of the nitrogen polar-first layer and the material of the nitrogen polar first layer and a thickness of the second nitrogen polar layer of Group IIIN material are selected such that, at the interface between the nitrogen polar first layer and the second nitrogen polar layer of Group IIIN material, net positive polarization charge is sufficient to induce a 2D electron gas (2DEG); wherein a thickness of the third nitrogen polar layer and the material of the nitrogen polar third layer and the thickness of the nitrogen polar second layer of Group IIIN material arc selected such that, at an interface between the nitrogen polar second layer of group III material and the nitrogen polar third layer, in the absence of n-doping, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A density of the n-doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form the interface between the nitrogen polar third layer and the nitrogen polar second layer of Group IIIN material.

[0113] Figure 9 shows a schematic of another instantiation of the quantum well structure of these teachings. Referring to Figure 9, in the instantiation shown therein, the quantum well structure shown therein has a nitrogen polar first layer, AIN. The quantum well structure shown therein also has a nitrogen polar second layer of Group IIIN material, GaN, epitaxially deposited on the nitrogen polar first layer. A nitrogen polar third layer, AIN, is epitaxially deposited on the second nitrogen polar layer. The nitrogen polar second layer, GaN, has an n-doped section. A thickness of the nitr ogen polar first AIN layer and a thickness of the second nitr ogen polar layer of Group IIIN material, GaN, are selected such that in the absence of n-doping, a net positive polarization charge is sufficient to induce a 2D electron gas (2DEG). A thickness of the nitrogen polar third layer, AIN, andDocket No.: 11208-02the thickness of the nitrogen polar second layer of Group IIIN material are selected such that, at an interface between the nitrogen polar second layer of group III material and the nitrogen polar third AIN layer, in the absence of n-doping, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A density of the n-doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form the interface between the nitrogen polar third AIN layer and the nitrogen polar second layer of Group IIIN material.

[0114] In one instance, in the instantiation of the quantum well structure of these teachings shown in Fig. 9, n-doping is n-8-doping. That instance is shown in Figure 9C. Referring to Figure 9C, in the instantiation shown therein, the quantum well structure shown therein has a nitrogen polar first layer, AIN. The quantum well structure shown therein also has a nitrogen polar second layer of Group IIIN material, GaN, epitaxially deposited on the nitrogen polar first layer. The nitrogen polar second layer. GaN, has n-6-a doped section at an interface between nitrogen polar third layer and the nitrogen polar second layer of Group IIIN material, GaN. A nitrogen polar third layer, AIN, is epitaxially deposited on the nitrogen polar second layer. A thickness of the nitrogen polar third layer, AIN, and the thickness of the nitrogen polar-second layer of Group IIIN material are selected such that, at an interface between the nitrogen polar-second layer of group III material and the nitrogen polar third AIN layer, in the absence of n-6-doping, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A surface density of the n-6-doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form the interface between the nitrogen polar third AIN layer and the nitrogen polar second layer of Group IIIN material.

[0115] Figure 9 A shows a schematic of yet another instantiation of the quantum well structure of these teachings. Referring to Figure 9A, in the instantiation shown therein, the quantum well structure shown therein has a nitrogen polar first layer, AIN. The quantum well structure shown therein also has a nitrogen polar second layer of Group IIIN material, GaN, epitaxially deposited on the nitrogen polar first layer. A nitrogen polar third layer, AIN, is epitaxially deposited on the nitrogen polar-second layer. The nitrogen polar third layer, AIN, has n-doped section . A thickness of the nitrogen polar third layer, AIN, and the thickness of the nitrogen polar second layer of Group IIIN material are selected such that, at an interface between the nitrogen polar second layer of group III material and the nitrogen polar third AIN layer, in the absence of n-doping, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A density of the n-doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form the interface between the nitrogen polar third AIN layer and the nitrogen polar second layer of Group IIIN material.Docket No.: 11208-02

[0116] For the nitrogen polar quantum well structure illustrative instantiations with n-doping shown above, in one instance, the Group IIIN material is gallium nitride, the material of the metal polar first layer is AIN, and the material of the metal polar third layer is AIN.

[0117] For the nitrogen polar quantum well structure with n-doping disclosed above, in other instances, the Group 111N material is InN. In further instances, the Group 111N material is one of (GaxIni-x)N, (AlxGanx)N, or (AlxInix)N. In still other instances, the material of the metal polar third layer is one of AlxGaixN, AlxScixN, AlxYrxN, or AlxLaixN. In some of those still other instances, the Group IIIN material is GaN.

[0118] In one instance, in the instantiation of the quantum well structure of these teachings shown in Fig. 9 A, n-doping is n-6-doping. That instance is shown in Figure 9B. Referring to Figure 9B, in the instantiation shown therein, the quantum well structure shown therein has a nitrogen polar first layer, AIN. The quantum well structure shown therein also has a nitrogen polar second layer of Group IIIN material, GaN, epitaxially deposited on the nitrogen polar first layer. A nitrogen polar third layer, AIN, is epitaxially deposited on the nitrogen polar-second layer. The nitrogen polar third layer, AIN, has an n-6-doped section at an interface between nitrogen polar third layer and the nitrogen polar second layer of Group IIIN material, GaN. A thickness of the nitrogen polar third layer, AIN, and the thickness of the nitrogen polar second layer of Group IIIN material are selected such that, at an interface between the nitrogen polar second layer of group III material and the nitrogen polar third AIN layer, in the absence of n-8-doping, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A surface density of the n-8-doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form the interface between the nitrogen polar-third AIN layer and the nitrogen polar second layer of Group IIIN material.

[0119] Figure 9D shows an instance of the instantiation of the quantum well structure of these teachings shown in Fig. 9A, in which the Group IIIN material is one of GaN or InN (GaN in the instance shown), and in which the nitrogen polar first layer has a nitrogen polar sub-layer, the nitrogen polar sub-layer including one of AlxGaixN, AlxInrxN, AIxSc].xN, AIXB|XN. AlxYi-xN, or AlxLaixN, and an AIN interlayer epitaxially deposited on the nitrogen polar sub-layer, the AIN interlayer being disposed between the nitrogen polar sub-layer and the nitrogen polar second layer of Group IIIN material. Similar instantiations, for the instantiation of the quantum well structure of these teachings shown in Fig. 9, are within the scope of these teachings.

[0120] In yet another instantiation, the method of these teachings for fabricating a semiconductor quantum well structure includes epitaxially depositing a nitrogen polar first layer, a material of the nitrogen polar first layer including at least one of AIN, AlxGaixN, AlxInrxN, AlxSciDocket No.: 11208-02XN, AlxBi xN, AlxYi xN, or ALLai xN, epitaxially depositing a nitrogen polar second layer of Group IIIN material on the nitrogen polar first layer, epitaxially depositing a nitrogen polar-third layer on the second nitrogen polar layer, a material of the third nitrogen polar layer including one of AIN, AlxGaiXN, AlxInixN, AlxSci xN, AlxBi-xN, AlxYi_xN, or AlxLai-xN, n-doping one of a section of the material of the nitrogen polar third layer or a section of the material of the nitrogen polar third layer. A thickness of the nitrogen polar first layer and the material of the nitrogen polar-first layer and a thickness of the second nitrogen polar layer of Group IIIN material are selected such that, at the interface between the nitrogen polar first layer and the second nitrogen polar layer of Group IIIN material, net positive polarization charge is sufficient to induce a 2D electron gas (2DEG). A thickness of the third nitrogen polar-layer and the material of the nitrogen polar third layer and the thickness of the nitrogen polar second layer of Group IIIN material are selected such that, at an interface between the nitrogen polar second layer of group Ill material and the nitrogen polar third layer, in the absence of n-8-doping, a net negative polarization charge is sufficient to induce a 2D hole gas. (2DHG). A density of the n-doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form the interface between the nitrogen polar third layer and the nitrogen polar second layer of Group IIIN material.

[0121] In yet another instantiation, the method of these teachings for fabricating a semiconductor quantum well structure includes epitaxially depositing a nitrogen polar first layer, a material of the nitrogen polar first layer comprising one of AIN, AlxGaixN, AlxIni-xN, AlxSci-xN, AlxBi-xN, AIxYi-xN, or AlxLaixN, epitaxially depositing a nitrogen polar second layer of Group IIIN material on the nitrogen polar first layer, epitaxially depositing a pre-determined portion of a nitrogen polar third layer on the second nitrogen polar-layer, a material of the third nitrogen polar-layer comprising one of AIN, AlxGaixN, AlxIni xN, AlxSci.xN, AlxBi.xN, AlxYi.xN, or AlxLaixN, n-6-doping one of a section of the material of the nitrogen polar third layer or a section of the material of the pre-determined portion of the nitrogen polar third layer at an interface between nitrogen polar third layer and the nitrogen polar second layer of Group IIIN material, and epitaxially depositing a remainder portion of the nitrogen polar third layer on the pre-determined portion of nitrogen polar third layer. A thickness of the nitrogen polar first layer and the material of the nitrogen pola-first layer and a thickness of the second nitrogen polar layer of Group IIIN material are selected such that, at the interface between the nitrogen polar first layer and the second nitrogen polar layer of Group IIIN material, net positive polarization charge is sufficient to induce a 2D electron gas (2DEG). A thickness of the third nitrogen polar layer and the material of the nitrogen polar third layer and the thickness of the nitrogen polar second layer of Group IIIN material are selected such that, at an interface between the nitrogen polar-second layer of group III material and the nitrogen polar thirdDocket No.: 11208-02layer, in the absence of n-6-doping, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A surface density of the n-8-doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form the interface between the nitrogen polar third layer and the nitrogen polar second layer of Group IIIN material.

[0122] A flowchart representation of the yet another instantiation of the method of these teachings is shown in Figure 10. Referring to Figure 10, in the instantiation shown therein, a nitrogen polar first layer is epitaxially deposited on a substrate (step 610, Fig. 10). A material of the nitrogen polar first layer includes one of AIN, AlxGaixN, AlxInixN, AlxSci-xN, AlxBjxN, A1XY|.XN, or AlxLaiXN. A nitrogen p lar second layer of Group IIIN material is epitaxially deposited on the nitrogen polar first layer (step 620, Fig. 10). A nitrogen polar thud layer is epitaxially deposited on the nitrogen polar second layer (step 630, Fig. 10). A material of the third nitrogen polar layer includes one of AIN, AlGaN, AllnN, AlScN, A1BN, A1YN, or AlLaN. One of a section of the pre-determined portion of the nitrogen polar thud layer or a section of the nitrogen polar second layer at an interface between nitrogen polar third layer and the nitrogen polar second layer of Group IIIN material is n-doped (step 640, Fig. 10). A thickness of the nitrogen polar first layer and the material of the nitrogen polar first layer and a thickness of the nitrogen polar second layer of Group IIIN material are selected such that, at the interface between the nitrogen polar first layer and the nitrogen polar second layer of Group IIIN material, net positive polarization charge is sufficient to induce a 2D electron gas (2DEG). A thickness of the nitrogen polar third layer and the material of the nitrogen polar third layer and the thickness of the nitrogen polar second layer of Group IIIN material are selected such that, at an interface between the nitrogen polar second layer of group III material and the nitrogen polar third layer, in the absence of n-doping, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG). A density of the n-doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form at the interface between the nitrogen polar third layer and the nitrogen polar second layer of Group IIIN material.

[0123] In one instance, n-doping, in the instantiation of the method of these teachings shown in Figure 10, is n-6-doping. That instance of the method of these teachings is shown in Figure 10A. Referring to Figure 10 A, in the instantiation shown therein, a nitrogen polar first layer is epitaxially deposited on a substrate (step 610, Fig. 10A). (Steps identical to those of Figure 10 are given the same number as in Figure 10.) A material of the nitrogen polar first layer includes one of AIN, AlxGaiXN, AlxIni-xN, AlxSci xN, AlxBi-xN, AlxYi-xN, or AlxLaixN. A nitrogen polar second layer of Group IIIN material is epitaxially deposited on the nitrogen polar first layer (step 620, Fig. 10A). A predetermined portion of a nitrogen polar third layer is epitaxially deposited on the nitrogen polar second layer (step 635, Fig. 10A). A material of the third nitrogen polar layer includes one of AIN, AlGaN,Docket No.: 11208-02AllnN, AlScN, A1BN, A1YN, or AlLaN. One of a section of the pre-determined portion of the nitrogen polar third layer or a section of the nitrogen polar second layer at an interface between nitrogen polar third layer and the nitrogen polar second layer of Group IIIN material is n-6- doped (step 645, Fig. 10A). A remainder portion of the nitrogen polar third layer is epitaxially deposited on the pre-determined portion of nitrogen polar third layer (step 660, Fig. 10A). A thickness of the nitrogen polar first layer and the material of the nitrogen polar first layer and a thickness of the nitrogen polar second layer of Group IIIN material are selected such that, at the interface between the nitrogen polar first layer and the nitrogen polar second layer of Group IIIN material, net positive polarization charge is sufficient to induce a 2D electron gas (2DEG). A thickness of the nitrogen polar third layer and the material of the nitrogen polar thud layer and the thickness of the nitrogen polar second layer of Group IIIN material are selected such that, at an interface between the nitrogen polar second layer of group III material and the nitrogen polar thud layer, in the absence of n-6-doping, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG).

[0124] A surface density of the n-6-doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form at the interface between the nitrogen polar third layer and the nitrogen polar second layer of Group IIIN material.

[0125] In some instances of the method for fabricating nitrogen polar semiconductor quantum well structures with n-doping, epitaxial deposition is performed by molecular beam epitaxy (MBE). In other instances, epitaxially depositing is performed by one of Metalorganic vapour-phase epitaxy (MOCVD), Hydride vapour-phase epitaxy (HVPE), or Reactive Sputtering. In some instances, the dopant used in n-doping is Si. In other instances, the dopant used in n-doping is Ge. In one instance, the substrate includes one of single crystal AIN, Si, SiC, an AIN template, or Sapphire. The method for fabricating nitrogen polar semiconductor quantum well structures with n-doping can be used for fabricating any instantiation of the nitrogen polar semiconductor quantum well structure with n-doping, including the ones disclosed above.

[0126] For the purposes of describing and defining the present teachings, it is noted that the term “'substantially" is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The term "substantially" is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.Docket No.: 11208-02

[0127] Although the invention has been described with respect to various embodiments, it should be realized these teachings arc also capable of a wide variety of fur ther and other embodiments within the spirit and scope of the appended claims.

Claims

Docket No.: 11208-02WHAT IS CLAIMED IS:

1. A semiconductor quantum well structure comprising:a metal polar first layer; a material of the metal polar first layer comprising one of AIN, AlxGai-xN, AlxIni-xN, AlxSci.xN, AlxBixN, AlxYi-xN, or AlxLai.xN;a metal polar second layer of Group IIIN material epitaxially deposited on the metal polar first layer;wherein at least one the metal polar first layer or the metal polar second layer comprises an n-doped section; and,a metal polar third layer epitaxially deposited on the metal polar second layer of Group IIIN material; a material of the metal polar-third layer comprising at least one of AIN, AlxGaixN, AlxIni-XN, AlxSci-xN, AlxBrxN , AlxYi.xN, or AlxLai.xN;wherein a thickness of the metal polar first layer and the material of the metal polar first layer and a thickness of the metal polar second layer of Group IIIN material are selected such that, in absence of the n-doped section, at an interface between the metal polar first layer and the metal polar second layer of Group IIIN material, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG); wherein a thickness of the metal polar third layer and the material of the metal polar-third layer and the thickness of the metal polar second layer of Group IIIN material are selected such that, at an interface between the metal polar second layer of group 111 material and the metal polar third layer, a net positive polarization charge induces a 2D electron gas (2DEG);wherein a density of the n-doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form the interface between the metal polar-first layer and the metal polar-second layer of Group IIIN material; andwherein the material of the metal polar first layer, the Group IIIN material, and the material of the metal polar third layer are selected to form a semiconductor quantum well structure.

2. The semiconductor quantum well structure of claim 1 , wherein the Group IIIN material is GaN.

3. The semiconductor quantum well structure of claim 2, wherein the material of the metal polar first layer is AIN.

4. The semiconductor quantum well structure of claim 3, wherein a material of the metal polar third layer is AIN.Docket No.: 11208-025. The semiconductor quantum well structure of claim 1, wherein the n-doped section is an n-8-doped section at an interface between the metal polar first layer and the metal polar second layer of Group IIIN material.

6. The semiconductor quantum well structure of claim 5, wherein the Group IIIN material is GaN, the material of the metal polar first layer is AIN, and the material of the metal polar third layer is AIN.

7. The semiconductor quantum well structure of claim 6, wherein a n-8-doping surface density is between about 4.75 x 1013cm-2to about 5.25 x 1013cm—2.

8. The semiconductor quantum well structure of claim 7, wherein the semiconductor quantum well structure has a mobility greater than 800.0 cm2 / Vs at room temperature (290 °K).

9. The semiconductor quantum well structure of claim 1 , wherein the material of the metal polar-third layer comprises one of AlxGaixN, AlxScixN, AlxYi-xN, AlxIni-xN, AlxBixN, or AlxLai-xN.

10. The semiconductor quantum well structure of claim 1 , wherein the material of the metal polar first layer comprises one of AlxGaixN, AlxScixN, AlxY |.xN, AlxInixN, A1XB jxN, or AlxLaixN.

11. The semiconductor quantum well structure of claim 1 , wherein the Group IIIN material is InN.

12. The semiconductor quantum well structure of claim 1, wherein the Group IIIN material is one of (Gaxhii.x)N, (AlxGai-x)N, or (AlxIni-x)N.

13. The semiconductor quantum well structure of claim 7, wherein the Group IIIN material is GaN.

14. A high electron mobility transistor (HEMT) that comprises the semiconductor quantum well structure of claim 1.Docket No.: 11208-0215. The high electron mobility transistor (HEMT) of claim 14, wherein the Group IIIN material is GaN.

16. The high electron mobility transistor (HEMT) of claim 15, wherein the material of the metal polar first layer is AIN.

17. The high electron mobility transistor (HEMT) of claim 16, wherein the material of the metal polar third layer is AIN.

18. The semiconductor quantum well structure of claim 1, further comprising a Group IIIN material cap layer epitaxially deposited on the metal polar third layer.

19. The semiconductor quantum well structure of claim 18, wherein the Group IIIN material cap layer is a GaN cap layer.

20. The semiconductor quantum well structure of claim 1 , wherein the Group IIIN material is one of GaN or InN ; and wherein the metal polar third layer comprises an AIN interlayer epitaxially deposited on the metal polar second layer of Group IIIN material and a metal polar sublayer epitaxially deposited on the AIN interlayer, the metal polar sub-layer comprising one of AlxGaiXN, AlxIni xN, AlxSc xN, AlxB|xN, AlxYi.xN, or AlxLai.xN.

21. The high electron mobility transistor (HEMT) of claim 16, wherein the n-doped section is an n-8-doped section at an interface between the metal polar first layer and the metal polar second layer of Group IIIN material.

22. A method for fabricating a semiconductor quantum well structure, the method comprising:epitaxially depositing a metal polar first layer on a substrate; a material of the metal polar first layer comprising one of AIN, AlxGaixN, AlxIn].xN, AlxSci-xN, AlxBi-xN, AlxYi.xN, or AlxLai.xN;epitaxially depositing a metal polar second layer of Group IIIN material on the metal polar first layer;n-doping one of a section of the material of the metal polar first layer or a section of the material of the metal p lar second layer;Docket No.: 11208-02epitaxially depositing a metal polar third layer on the metal polar second layer of Group IIIN material; a material of the metal polar third layer comprising at least one of AIN, AlxGaixN, AlxIniXN, AlxSci.xN, AlxBi.xN, A1XY,.XN, or AlxLa,.xN;wherein a thickness of the metal polar-first layer and the material of the metal polar-first layer and a thickness of the metal polar second layer of Group IIIN material are selected such that, in absence of an n-doped section, at an interface between the metal polar first layer and the metal polar second layer of Group IIIN material, a net negative polarization charge is sufficient to induce a 2D hole gas (2DHG); wherein a thickness of the metal polar third layer and the material of the metal polar third layer and the thickness of the metal polar second layer of Group IIIN material are selected such that, at an interface between the metal polar-second layer of group III material and the metal polar-third layer, a net positive polarization charge induces a 2D electron gas (2DEG);wherein the material of the metal polar first layer, the Group IIIN material, and the material of the metal polar third layer are selected to form a semiconductor quantum well structure;wherein a density of the n-doped section is selected such that the 2DHG is suppressed and an additional electron channel does not form the interface between the metal polar-first layer and the metal polar second layer of Group IIIN material; andwherein the material of the metal polar first layer, the Group IIIN material, and the material of the metal polar third layer are selected to form a semiconductor quantum well structure.

23. The method of claim 22, wherein epitaxially depositing is performed by molecular beam epitaxy (MBE).

24. The method of claim 22, wherein epitaxially depositing is performed by one of Metalorganic vapour-phase epitaxy (MOCVD), Hydride vapour-phase epitaxy (HVPE), or Reactive Sputtering.

25. The method of claim 22, wherein a dopant used in the n-doping is Si.

26. The method of claim 22, wherein a dopant used in the n-doping is Ge.

27. The method of claim 22, wherein the Group IIIN material is GaN.

28. The method of claim 22, wherein the material of the metal polar first layer is AIN.Docket No.: 11208-0229. The method of claim 22, wherein the material of the metal polar third layer is AIN.

30. The method of claim 22, wherein the material of the metal polar third layer is one of AlxGai-xN, AlxIni-xN, AlxSci.xN, AlxBixN , A1XY].XN, or AlxLaixN.

31. The method of claim 22, wherein the material of the metal polar first layer is one of AlxGai.xN. AlJm-xN, AlxSci.xN, AlxBi.xN , AlxYl xN, or AlxLarxN.

32. The method of claim 22, wherein the Group IIIN material is InN.

33. The method of claim 22, wherein the Group IIIN material is one of (Gaxhi].x)N, (AlxGai.x)N, or (Alxlm_x)N.

34. The method of claim 22, wherein the substrate comprises one of single crystal AIN, Si, SiC, AIN template, or Sapphire.

35. The method of claim 22, wherein n-doping is n-6- doping; and wherein epitaxially depositing the metal polar second layer of Group IIIN material on the metal polar first layer comprises:epitaxially depositing a pre-determined portion of the metal polar second layer of Group IIIN material on the metal polar first layer;n-3-doping one of a section of the material of the metal polar-first layer or a section of the material of the pre-determined portion of a metal polar second layer at an interface between the metal polar first layer and the metal polar second layer of Group IIIN material; andepitaxially depositing a remainder portion of the metal polar second layer of Group IIIN material on the pre-determined portion of the metal polar second layer of Group IIIN material.

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