AlN channel heterostructure field-effect transistor

Abstract

The semiconductor device comprises a substrate and an orthorhombic polar crystalline oxide κ-AlN epitaxially and heterogeneously integrated on a wurtzite single crystal III-nitride layer comprising AlN disposed on the substrate. 2 O 3 The layer.

Description

[Technical Field]

[0001] The present disclosure relates generally to depletion-mode high electron mobile field effect transistor (HEMT) semiconductor devices, and more particularly to depletion-mode HEMT semiconductor devices having Schottky junction layers. [Background technology]

[0002] As is known in the art, active semiconductor devices such as diodes and FETs (field effect transistors) based on III-nitride materials, such as GaN, AlGaN, InN, AlN, and ScAlN, have demonstrated excellent RF / microwave performance, achieved with optimization of materials, processes, devices, and design techniques.

[0003] Transistor efficiency determines RF system range, sensitivity, power consumption, and reliability, and operating at higher power densities results in higher power dissipation (P diss It is desirable to improve transistor power and efficiency performance, otherwise applications are potentially limited due to thermal management. Summary of the Invention

[0004] According to the present disclosure, there is provided a semiconductor device including: an orthorhombic polar crystalline oxide κ-Al2O3 layer epitaxially and heterogeneously integrated on a wurtzite single crystalline III-nitride layer comprising AlN; a source electrode disposed over a conductive region in the polar κ-Al2O3 layer and a pathway into the AlN; a drain electrode disposed over a conductive region in the polar κ-Al2O3 layer and a pathway into the AlN; and a gate electrode disposed on top of the polar κ-Al2O3 layer between the source and drain electrodes.

[0005] In one embodiment, the upper layer is κ-B2O3 or κ-Al2O3 and κ-Al2O3 and κ-B2O3 (e.g., κ-(Al x B 1-x2 O3) Includes alloys.

[0006] In another embodiment, a semiconductor structure is provided in which a polarization discontinuity at the heterointerface between κ-Al 2 O 3 and AlN exists to induce a two-dimensional electron gas (2DEG) on the AlN side of the heterointerface.

[0007] The inventors have recognized the advantages of using an AlN channel layer in conjunction with a higher bandgap short-circuit barrier layer in place of a GaN channel layer to support ultra-high power density radio frequency (RF) transistors, taking advantage of the large breakdown and thermal conductivity properties of AlN.

[0008] Furthermore, the inventors have recognized the benefit of an AlN channel layer in conjunction with a k-Al2O3 barrier layer, resulting in an overall larger polarization discontinuity and bandgap.

[0009] The details of one or more embodiments of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view of a semiconductor device according to the present disclosure. [Figure 2A] 1 is a chart showing various properties of different materials, including GaN and AlN. [Figure 2B] 2B is a plot showing breakdown voltage for various materials from the chart in FIG. 2A. DETAILED DESCRIPTION OF THE INVENTION

[0011] Like reference symbols in the various drawings indicate like elements.

[0012] Before beginning with a detailed description of the invention, it should be noted that the inventors have recognized the advantages of replacing the GaN channel with AlN and using a polar oxide (kappa-phase Al2O3 or K-Al2O3) as a barrier layer to provide a carrier density in the AlN that is 10 times greater through polarization. Using AlN as a channel layer allows for four times greater field strength than GaN, thus allowing voltage scaling by four times, and has a conductivity that is 2.5 times greater than GaN for improved thermal management. Homoepitaxy is possible with currently existing AlN substrates.

[0013] This disclosure involves a kappa-phase heterostructure as a barrier layer to an AlN channel. The extremely strong polarization of Al2O3 (AlN, 9 times higher than that of GaN and 3 times higher) with an AlN channel (2.5 times higher thermal conductivity and 4 times higher electric field strength than GaN (P. Ranga et al., "Highly tunable, polarization-engineered two-dimensional electron gas in ε-AlGaO3 / ε-Ga2O3 heterostructures," Appl. Phys. Exp. 13 061009 (2020)) improves thermal conductivity to handle higher heat dissipation, which other technologies cannot achieve without resorting to integration in diamond, and solves the problem of transmitting up to 40 times the power density of state-of-the-art GaN structures. Furthermore, AlN is more closely lattice-matched to diamond, so the process of integrating kappa-Al2O3 / AlN on diamond is simpler. AlN substrates are commercially available, so homoepitaxy is possible.

[0014] As described, the structure improves power dissipation handling for integration into transistors, while enabling power densities up to 40 times higher than current GaN structures. The latter addresses and mitigates heat dissipation issues with current ultra-high power transistors being pushed to power capabilities in excess of 8 W / mm, where thermal cooling solutions currently limit their use to short duty cycle pulsed applications only.

[0015] Despite its higher thermal conductivity and potential for ultra-high power density performance, diamond has not shown promise for decades because it suffers from low carrier density and mobility, resulting in transistors with much lower performance than current state-of-the-art GaN structures. Other semiconductor technologies that show more promise for ultra-high power density performance than GaN suffer from poor thermal conductivity, relying on complex processes to integrate those semiconductors into diamond. None of those technologies have the mobility combined with high predicted carrier density and high thermal conductivity in one semiconductor platform.

[0016] As explained, due to the high polarization properties of orthorhombic κ-AlO (three times that of AlN), but a large bandgap of 7.7 eV (1.5 eV higher than AlN), κ-B2O3 has an even larger bandgap of 11.3 eV and can also be used as a barrier layer (see Appl. Phys. Lett. 117, 012104 (2020); https: / / dol.org / 10.1063 / 5.0005808; Submitted: 25 February 2020. Accepted 28 June 2020. Published Online: 09 July 2020).

[0017] 1, there is shown a semiconductor structure 10 having a depletion-mode (D-mode) field effect transistor 12, here a D-mode HEMT. The D-mode HEMT 12 includes a source electrode 26, a drain electrode 28, and a gate electrode 25 disposed between the source electrode 26 and the drain electrode 28, as shown.

[0018] More specifically, the semiconductor structure 10 includes a single-crystal substrate 18, here, for example, silicon (Si), silicon carbide (SiC), diamond, or aluminum nitride (AlN), an epitaxially grown AlN layer 22 that forms the nucleation, buffer, and channel regions of the HEMT structure, and one or more epitaxially grown polar oxide barrier materials, here, κ-AlO or, as described below, alternatively, κ-B2O3, as barrier layers 24. The oxide-nitride heterolayers 22 and 24 form a heterojunction that results in a 2DEG channel (indicated by dotted line 23) within the AlN layer 22. Note that the polar oxide layer 24 extends from an ohmic contact region 27 of the source electrode 26 to an ohmic contact region 29 of the drain electrode 28. A gate electrode 25 forms a Schottky junction with the polar oxide layer 24. It should also be noted that the source electrode 26 and the drain electrode 28 make ohmic contact with the AlN channel layer 22 through ohmic contact regions 27 and 29, respectively. Conventional ohmic contact formation, which involves thermal annealing of metal contacts directly bonded to a Schottky barrier, is not feasible due to the lack of a κ-Al2O3 barrier, a mechanism involving the formation of nitrogen vacancies and elemental intermixing of the electrode and barrier material during thermal annealing that renders the barrier layer in III-nitride HEMTs form ohmic contact regions between the electrode and barrier material. Formation of the ohmic contact regions 27 and 29 in this structure is achieved by either an ohmic recess or regrowth configuration, with the ohmic contact regions 27 and 29 being either an ohmic recess deposited by epitaxy techniques (e.g., molecular beam, metalorganic chemical vapor, physical vapor) in the case of an ohmic regrowth where either material interfaces with the 2DEG, as shown in FIG. 1, or the same source electrode material 26 and drain electrode material 28 deposited by e-beam evaporation in the case of a conductive AlN layer. In either case, an etch is performed to remove a small portion of the barrier material and AlN channel in the areas where the source and drain electrodes will be deposited.Instead, regions 27 and 29 are rendered without etching or removal of either the K-Al2O3 or AlN by ion implantation of an appropriate ion species (e.g., Si) that enables ohmic contact formation. After forming source electrode 26 and drain electrode 28, gate electrode 25 is formed in Schottky contact with barrier layer 24, as shown.

[0019] 2A and 2B, replacing AlN with GaN as the channel material enables extremely high voltages in highly scaled transistors due to its much greater breakdown strength compared to GaN (3x greater than GaN), maintains high gain at high voltages due to the stronger carrier confinement of AlN vs. GaN, and provides more efficient transistors due to its higher thermal conductivity (2x greater than GaN) for improved thermal management; employing an AlN substrate further improves thermal management. Such structures offer 10x better R compared to existing (SiC, GaN) and emerging (β-Ga2O3) technologies for high power switching applications. ON -V BRK The table and plots in Figures 2A and 2B, respectively, are from JY Tsao, Adv. Electron. Mat., vol. 04, 1600501, 2018. Although orthorhombic κ-Al2O3 has high polarization (approximately three times larger than AlN), its large bandgap of 7.7 eV (1.5 eV higher than AlN) allows for extremely high voltage operation. κ-B2O3 has an even larger bandgap of 11.3 eV and can also be used as a barrier layer.

[0020] It should be noted that a high density 2DEG is possible assuming the polarization of the K-AlO barrier layer 24 is in the same direction as the AlN channel layer 22. In one embodiment, the K-AlO barrier layer is in the range of 3-15 nm, here approximately 4 nm thick.

[0021] The k-Al2O3 / AlN HEMT structure has been described above. Assuming that the band gap of the latter is larger than that of AlN, the k-Al2O3 barrier layer 24 is k-B2O3, k-(Al x B 1-x )2O3, or alternatively, κ-(Al x B y Ga 1-x-y It should be noted that the SiO 2 layer can be replaced by a SiO 2 layer.

[0022] Several embodiments of the disclosure have been described. However, it will be understood that various modifications can be made without departing from the spirit and scope of the present disclosure. The composition of the channel and barrier layers need not be the same throughout and may consist of multiple layers, multiple combinations of group III elements, or gradients of group III element composition. Furthermore, it should be understood that other single-crystal substrates 18 can be used that enable deposition of AlN with a single, well-defined crystalline orientation relative to the crystal structure of the substrate 18. This includes heterojunction structures formed through the deposition of one or more crystalline materials on another, or by bonding one or more layers together to define a surface region that is crystalline and supports the crystalline growth of AlN. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. A semiconductor device comprising: a polar oxide layer epitaxially and heterogeneously integrated on a wurtzite single crystal III-nitride layer comprising AlN; a source electrode disposed across a first conductive region formed in the polar oxide layer and a path into the AlN; a drain electrode disposed across a second conductive region formed in the polar oxide layer and a path into the AlN; a gate electrode disposed on top of the polar oxide layer and between the source electrode and the drain electrode; and the semiconductor device, wherein the first and second conductive regions each have a bottom end that extends into the wurtzite single crystalline III-nitride layer, but the bottom ends do not extend completely through the wurtzite single crystalline III-nitride layer.

2. The polar oxide layer is κ-Al ２ O ３ and κ-B ２ O ３ 10. The semiconductor device of claim 1, comprising an alloy of:

3. The polar oxide layer is κ-B ２ O ３ The semiconductor device of claim 1 , comprising:

4. 2. The semiconductor device of claim 1, wherein the polar oxide layer comprises k-Al 2 O 3 .

5. The semiconductor device of claim 1 , wherein the polar oxide layer has a thickness of 3 to 15 nm.

6. 10. The semiconductor device of claim 1, wherein the semiconductor device is a depletion mode field effect transistor.

7. A semiconductor device comprising: A substrate; a polar oxide layer epitaxially and heterogeneously integrated on a wurtzite single crystal III-nitride layer comprising AlN disposed on the substrate; a source electrode disposed across a first conductive region formed in the polar oxide layer and a path into the AlN; a drain electrode disposed across a second conductive region formed in the polar oxide layer and a path into the AlN; a gate electrode disposed between the source electrode and the drain electrode to provide a depletion mode field effect transistor; and the semiconductor device, wherein the first and second conductive regions each have a bottom end that extends into the wurtzite single crystalline III-nitride layer, but the bottom ends do not extend completely through the wurtzite single crystalline III-nitride layer.

8. The semiconductor device of claim 7, wherein the polar oxide layer has a thickness in the range of 3 to 15 nm.

9. The semiconductor device of claim 8 , wherein the source electrode and the drain electrode form ohmic contacts with the AlN.

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