High-conductivity n-type AlGaN structure and preparation method and application thereof

Abstract

The invention discloses a high-conductivity n-type AlGaN structure and a preparation method and application thereof. In the preparation process of the n-type AlGaN, the incorporation of the donor impurities is periodically modulated, and a doped layer and non-doped layer alternate epitaxial structure is formed in the n-type AlGaN, so that an electron generation layer and a transport layer are spatially separated. While the electron concentration in the n-type AlGaN is ensured, the ionization impurity scattering in the electron transport process is effectively reduced, the electron mobility is improved, and the conductivity of the n-type AlGaN is further improved. The n-type AlGaN structure provided by the invention has the advantages of high conductivity, atomic-scale flatness of surface morphology and the like, and the preparation method is good in repeatability and suitable for vigorous popularization.

Description

Technical Field

[0001] The present invention belongs to the technical field of III-nitride semiconductor preparation, and particularly relates to an n-type AlGaN structure with high conductivity and an atomically flat surface morphology, and a preparation method and application thereof. Background Art

[0002] In recent years, driven by applications such as sterilization, biological medicine, and printing, AlGaN-based ultraviolet optoelectronic devices, especially ultraviolet light-emitting diodes (UV-LEDs), have attracted extensive academic and industrial attention. They have the characteristics of environmental protection, small size, low energy consumption, and long service life, and are considered to be one of the most promising fields and industries of III-nitride semiconductors at present.

[0003] At present, the flip-chip structure is the main configuration of AlGaN-based UV-LED devices. This configuration has problems such as a long current lateral expansion distance, which in turn leads to a large operating voltage of the device, hindering the further improvement of the electro-optical conversion efficiency. One of the root causes of this problem is that the conductivity of the high-Al-component n-type AlGaN that satisfies ultraviolet light transmission is relatively low.

[0004] Conductivity is jointly determined by the carrier (electron or hole) concentration and mobility. Taking Si-doped n-type AlGaN as an example, the electron concentration depends on the ionization efficiency of Si donor impurities and the compensation effect of acceptor defects on electrons in the material. At present, through the optimization of epitaxial growth conditions, the electron concentration in n-type AlGaN with an Al component lower than 84% can reach 10 19 cm -3 order of magnitude. However, for the electron mobility, there is still a lack of effective improvement methods at present. Summary of the Invention

[0005] The present invention studies and finds that in the existing epitaxial methods, the continuous introduction of Si donor impurities makes the spatial coincidence of the electron generation layer and the transport layer in n-type AlGaN. During the electron transport process, the electrons are inevitably scattered by the ionized Si impurities, thereby reducing the electron mobility; and when increasing the Si impurity concentration to pursue a higher electron concentration, it will cause a further reduction in the electron mobility. It can be seen that the spatial coincidence of the electron generation layer and the transport layer in n-type AlGaN is the root cause of the difficulty in improving the conductivity. Therefore, in order to improve the conductivity of n-type AlGaN, it is necessary to achieve the spatial separation of the electron generation layer and the transport layer.

[0006] The purpose of the present invention is to provide a preparation method of high-conductivity n-type AlGaN, which can achieve the spatial separation of the electron generation layer and the transport layer, and the obtained n-type AlGaN has the characteristics of high conductivity and an atomically flat surface morphology.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] In a first aspect, the present invention provides an n-type AlGaN structure, comprising an n-type AlGaN layer; the n-type AlGaN layer is a periodically alternating structure of doped layers / undoped layers.

[0009] The donor impurity in the doped layer is Si or Ge;

[0010] The thickness of the doped layer is between 1 - 20 nm, preferably between 2 - 10 nm.

[0011] The thickness of the undoped layer is between 1 - 10 nm, preferably between 2 - 6 nm.

[0012] According to an embodiment of the present invention, the n-type AlGaN structure comprises the following components:

[0013] A substrate;

[0014] An AlN nucleation layer, located on the substrate;

[0015] An AlN template layer, located on the AlN nucleation layer;

[0016] A stress buffer layer, located on the AlN template layer;

[0017] The n-type AlGaN layer, located on the stress buffer layer.

[0018] Among them, the substrate includes a sapphire substrate, a SiC substrate, a Si substrate or an AlN substrate.

[0019] Among them, the stress buffer layer is an alternately multi-periodic structure of AlN / AlGaN, or a stepped AlGaN multi-layer structure with a changing Al composition; the average Al composition of the stress buffer layer is modulated according to the Al composition of the n-type AlGaN layer.

[0020] In a second aspect, the present invention further provides a method for preparing the above n-type AlGaN structure, comprising the following steps: during the epitaxial growth of n-type AlGaN, a donor impurity source is periodically introduced into the reaction chamber to form an alternately growing structure of doped layers and undoped layers, which is the n-type AlGaN layer.

[0021] The temperature of the n-type AlGaN epitaxial growth process is between 1000 - 1120 °C, preferably between 1020 - 1100 °C.

[0022] The reaction conditions such as the reaction chamber temperature, pressure, and total gas flow rate during the epitaxial growth process of the doped layer and the undoped layer are the same as those of the epitaxial growth process of a conventional continuously doped n-type AlGaN layer.

[0023] According to an embodiment of the present invention, the method for preparing the n-type AlGaN structure includes the following steps:

[0024] S1. Epitaxially grow an AlN nucleation layer on a substrate;

[0025] S2. Epitaxially grow an AlN template layer on the AlN nucleation layer;

[0026] S3. Epitaxially grow a stress buffer layer on the AlN template layer;

[0027] S4. Epitaxially grow the n-type AlGaN layer on the stress buffer layer.

[0028] In step S4, the growth conditions of the doped layer and the undoped layer are the same.

[0029] In a third aspect, the present invention further provides an optoelectronic device including the above-mentioned n-type AlGaN structure.

[0030] The optoelectronic device is an optoelectronic device for ultraviolet light emission and detection.

[0031] By periodically modulating the incorporation of donor impurities, the present invention introduces an undoped layer as an electron transport channel in n-type AlGaN, realizing the spatial separation of the electron generation layer and the transport layer. Specifically, after electrons are generated by the ionization of impurities in the doped layer, they diffuse towards the undoped layer under the action of the concentration gradient and finally form a steady-state distribution. Since there are no deliberately incorporated donor impurities in the undoped layer, that is, the scattering of ionized impurities can be ignored, the mobility of electrons diffusing into the undoped layer is greatly improved, thereby increasing the overall conductivity of n-type AlGaN.

[0032] The beneficial effects achieved by the present invention are as follows:

[0033] 1. By periodically modulating the incorporation of donor impurities, the present invention increases the conductivity of n-type AlGaN, and the obtained n-type AlGaN structure has advantages such as atomically flat surface morphology.

[0034] 2. The method for preparing n-type AlGaN provided by the present invention meets the requirements of high-performance ultraviolet optoelectronic devices, and has the characteristics of good repeatability and is suitable for wide promotion. Description of the Drawings

[0035] Figure 1 It is a flow chart of modulation doping epitaxy of the n-type AlGaN structure described in the specific embodiment. Specific Embodiment

[0036] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0037] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0038] Unless otherwise specified, the reagents, materials, instruments, etc. used in the following examples are all commercially available.

[0039] The present invention specifically provides a preparation method for a high-conductivity n-type AlGaN structure. The core idea mainly has an important step:

[0040] That is, during the epitaxial growth of n-type AlGaN, donor impurity (such as Si, Ge, etc.) sources are periodically introduced into the reaction chamber to form an alternating growth structure of doped layers and undoped layers in the n-type AlGaN, realizing the spatial separation of the electron generation layer and the transport layer.

[0041] Among them, the Al component content of the n-type AlGaN layer is 0 - 100%, and according to the different Al component contents, the corresponding materials are GaN, AlN, or AlGaN.

[0042] Among them, the epitaxial growth temperature of the n-type AlGaN layer is controlled between 1000 - 1120 °C, preferably between 1020 - 1100 °C;

[0043] Among them, the thickness of the doped layer in the n-type AlGaN is controlled between 1 - 20 nm, preferably 2 - 10 nm; the thickness of the undoped layer is controlled between 1 - 10 nm, preferably 2 - 6 nm;

[0044] Among them, during the epitaxial growth of the n-type AlGaN layer, the N source (ammonia, NH 3 ), Ga source (trimethylgallium, TMGa or triethylgallium, TEGa), Al source (trimethylaluminum, TMAl), and donor impurity source (silane, SiH 4 or germane, GeH 4 ) keep their flow rates unchanged;

[0045] Among them, during the epitaxial growth of the doped layer and the undoped layer in the n-type AlGaN layer, reaction conditions such as the reaction chamber temperature, pressure, and total gas flow rate remain unchanged.

[0046] As Figure 1 shown, the modulation doping epitaxial process of the above n-type AlGaN structure is as follows: t 1 +t 2 +t 3 +t 4 is the total time of one cycle, t 1 is the growth time of the doped layer in the n-type AlGaN; t 2is the time when the doped layer switches to the undoped layer. During this period, the Ga, Al sources and the donor impurity (Si or Ge) source are not introduced into the MOCVD reaction chamber to empty the residual donor impurity source in the reaction chamber. This time is relatively short, and the typical time is 2 - 5 s; t 3 is the growth time of the undoped layer. During this process, the growth conditions such as the flow rates and temperatures of the Ga and Al sources and the pressure in the reaction chamber are the same as those in t 1 process; t 4 is the time when the undoped layer switches to the doped layer. During this period, the Ga, Al sources and the donor impurity source are not introduced into the MOCVD reaction chamber. This time is relatively short, and the typical time is 1 - 5 s.

[0047] Example 1

[0048] This example provides a method for preparing high-conductivity n-type AlGaN, which meets the requirements of AlGaN-based UV-LEDs with a luminous wavelength of 280 nm, and specifically includes the following steps:

[0049] Sl: Place a sapphire substrate with a (0001) plane in the reaction chamber of an MOCVD device (3×2"Aixtron CCS FP-MOCVD); in an H 2 atmosphere, reduce the pressure in the reaction chamber to 50 mbar, and at the same time raise the growth temperature to 1100 °C for in-situ high-temperature treatment of the sapphire.

[0050] S2: Keep the pressure in the reaction chamber at 50 mbar, lower the epitaxial temperature to 950 °C, and epitaxially grow a 15-nm-thick AlN nucleation layer; raise the epitaxial temperature to 1230 °C and epitaxially grow a 1-μm-thick AlN template layer.

[0051] S3: Lower the epitaxial temperature to 1150 °C and epitaxially grow a 0.35-μm-thick AlN / Al 0.6 Ga 0.4 N alternating multi-period structure as a stress buffer layer.

[0052] S4: Lower the epitaxial temperature to 1070 °C and epitaxially grow a 1-μm-thick n-Al 0.6 Ga 0.4 N layer on the stress buffer layer. During this process, SiH 4 is periodically introduced into the reaction chamber to make the thickness of the doped layer in n-Al 0.6 Ga 0.4 N be 5 nm (the epitaxial time t 1 is 15 s), and the thickness of the undoped layer be 5 nm (the epitaxial time t 3 is 15 s), with a total of 100 cycles grown. Among them, the time t 2 when the doped layer switches to the undoped layer is 3 s, and the time t 4It is 2 s.

[0053] Comparative Example 1

[0054] This comparative example provides a preparation method of n-type AlGaN, which meets the requirements of AlGaN-based deep ultraviolet LEDs with a luminous wavelength of 280 nm, and specifically includes the following steps:

[0055] S1: Place a sapphire substrate with a (0001) plane in the reaction chamber of an MOCVD device (3×2"Aixtron CCS FP-MOCVD); in an H 2 atmosphere, reduce the pressure of the reaction chamber to 50 mbar, and at the same time raise the growth temperature to 1100 °C to perform in-situ high-temperature etching on the sapphire.

[0056] S2: Keep the pressure of the reaction chamber at 50 mbar, lower the epitaxial temperature to 950 °C, and epitaxially grow a 15-nm-thick AlN nucleation layer; raise the epitaxial temperature to 1230 °C and epitaxially grow a 1-μm-thick AlN template layer.

[0057] S3: Lower the epitaxial temperature to 1150 °C, and epitaxially grow a 0.35-μm-thick AlN / Al 0.6 Ga 0.4 N alternating multi-periodic structure as a stress buffer layer.

[0058] S4: Lower the epitaxial temperature to 1070 °C, and epitaxially grow a 1-μm-thick n-Al 0.6 Ga 0.4 N layer (the epitaxial time is 3000 s). During this process, SiH 4 is continuously introduced into the reaction chamber, and the flow rates of each source are exactly the same as those in Example 1 above.

[0059] Effect verification

[0060] Compare the n-type AlGaN structures obtained in Example 1 and Comparative Example 1:

[0061] (1) Electrical properties: The results of Hall effect testing (Van der Pauw method) show that the conductivity of the n-type AlGaN structure in Example 1 is 200 S / cm; the conductivity of the n-type AlGaN structure in Comparative Example 1 is 93 S / cm;

[0062] (2) Surface morphology: The surfaces of the n-type AlGaN structures in Example 1 and Comparative Example 1 both exhibit atomic steps, and the surface flatness reaches below 0.2 nm (3×3 μm 2 ).

[0063] As can be seen from the above test results, on the premise of ensuring atomic-level surface flatness, Example 1 has a higher conductivity compared to Comparative Example 1. This shows that the design solution proposed in the present invention, which periodically introduces donor impurity (such as Si, Ge, etc.) sources during the n-type AlGaN epitaxial process to form an alternating growth structure of doped layers and undoped layers, achieving spatial separation of the electron generation layer and the transport layer, can significantly improve the conductivity of the n-type AlGaN structure. It is suitable for being widely promoted to related industrial applications and has good practicality.

[0064] Although the present invention has been described in detail with general descriptions and specific embodiments above, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. An n-type AlGaN structure, comprising an n-type AlGaN layer; Characterized in that: The n-type AlGaN layer is a periodically alternating structure of doped layers / undoped layers.

2. The n-type AlGaN structure according to claim 1, Characterized in that: The donor impurity in the doped layer is Si or Ge.

3. The n-type AlGaN structure according to claim 1 or 2, Characterized in that: The thickness of the doped layer is between 1 - 20 nm.

4. The n-type AlGaN structure according to any one of claims 1 - 3, Characterized in that: The thickness of the undoped layer is between 1 - 10 nm.

5. The n-type AlGaN structure according to any one of claims 1 - 4, Characterized in that: The n-type AlGaN structure comprises the following components: A substrate; An AlN nucleation layer, located on the substrate; An AlN template layer, located on the AlN nucleation layer; A stress buffer layer, located on the AlN template layer; The n-type AlGaN layer, located on the stress buffer layer.

6. A method for preparing the n-type AlGaN structure according to any one of claims 1 - 5, comprising the following steps: During the epitaxial growth of n-type AlGaN, a donor impurity source is periodically introduced into the reaction chamber to form an alternating growth structure of doped layers and undoped layers, which is the n-type AlGaN layer.

7. The preparation method according to claim 6, Characterized in that: The temperature of the n-type AlGaN epitaxial growth process is between 1000 - 1120 °C.

8. The preparation method according to claim 6 or 7, Characterized in that: The growth conditions of the doped layer and the undoped layer are the same.

9. An optoelectronic device, comprising the n-type AlGaN structure according to any one of claims 1 - 5.

10. The optoelectronic device according to claim 9, Characterized in that: The optoelectronic device is an optoelectronic device for ultraviolet light emission / detection.

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