AlGaN-based ultraviolet light-emitting quantum dot structure and preparation method and application thereof

Abstract

The invention discloses an AlGaN-based ultraviolet light-emitting quantum dot structure and a preparation method and application thereof. The AlGaN-based ultraviolet light-emitting quantum dot structure provided by the invention comprises a periodic structure, the periodic structure is composed of an Al < x > Ga < 1-x > N quantum dot and an Al < y > Ga < 1-y > N barrier layer. According to the invention, the energy level position of each sub-band of a valence band is regulated and controlled through a quantum dot structure, the proportion of a heavy hole band in carrier radiation recombination is highlighted, the light-emitting polarization degree is effectively improved, and the light extraction efficiency of an ultraviolet light-emitting diode (UV-LED) is further improved; meanwhile, the carrier space confinement is enhanced, overlapping of electron and hole wave functions is enhanced, the quantum efficiency in the device is improved, and finally the electro-optical conversion efficiency of the UV-LED device is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of group III nitride semiconductors, and particularly relates to an AlGaN-based ultraviolet light-emitting quantum dot structure, a preparation method thereof, and an application thereof. Background Art

[0002] AlGaN materials are the best choice for preparing solid-state ultraviolet (UV) optoelectronic devices (such as light-emitting diodes, LEDs), and have wide applications in fields such as sterilization and disinfection, water and air purification, and biomedicine. It is one of the most promising fields and industries of group III nitride semiconductors at present. However, due to its low electro-optical conversion efficiency, it has become the main problem and difficulty restricting the application and popularization of UV-LEDs.

[0003] The electro-optical conversion efficiency depends on four factors: internal quantum efficiency, carrier injection efficiency, light extraction efficiency, and electrical efficiency. Among them, the internal quantum efficiency refers to the radiative recombination efficiency of the active region, which is improved by enhancing the material quality; for the carrier injection efficiency, through the reasonable design of the electron blocking layer in the UV-LED, the aggregation and recombination of electrons and holes in the active region can be effectively promoted. The light extraction efficiency is directly related to the light emission polarization degree of the device active region, packaging form, etc. At present, restricted by the low light emission polarization degree of the active region, that is, the proportion of the effectively extractable transverse electric (TE) mode is small, the light extraction efficiency of UV-LEDs is still low, which is one of the important factors restricting the improvement of the device electro-optical conversion efficiency. Summary of the Invention

[0004] The purpose of the present invention is to provide an AlGaN-based ultraviolet light-emitting quantum dot structure, which can be used as an active region to improve the light extraction efficiency of UV-LED devices, while strengthening the quantum confinement, effectively increasing the overlap of the electron and hole wave functions in the quantum dots, improving the internal quantum efficiency of the device, and ultimately improving the electro-optical conversion efficiency of UV-LED devices.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides an AlGaN-based ultraviolet light-emitting quantum dot structure, including a periodic structure;

[0007] The periodic structure is composed of Al x Ga 1-x N quantum dots and Al y Ga 1-y N barrier layers;

[0008] Wherein, 0.2 ≤ x ≤ 0.8 (x is determined according to the light emission wavelength requirement of the device), 0.3 ≤ y ≤ 1, y = x + b, and b ≥ 0.1.

[0009] The Al y Ga 1-y The thickness of the AlGaN barrier layer is 2 - 20 nm, preferably 4 - 12 nm.

[0010] The Al x Ga 1-x The size range of the AlGaN quantum dots is 20 - 300 nm, preferably 100 nm.

[0011] According to an embodiment of the present invention, the AlGaN - based ultraviolet light - emitting quantum dot structure sequentially includes the following components:

[0012] A substrate;

[0013] Al m Ga 1-m An AlGaN template layer, where 0 < m ≤ 1; when m = 1, the template layer is an AlN template layer;

[0014] Al y Ga 1-y An AlGaN barrier layer, where 0.3 ≤ y ≤ 1, y = x + b, and b ≥ 0.1;

[0015] Al x Ga 1-x An AlGaN dot - like structure, where 0.2 ≤ x ≤ 0.8.

[0016] In a second aspect, the present invention further provides a method for preparing an AlGaN - based ultraviolet light - emitting quantum dot structure, including the following steps:

[0017] S1. MOCVD - grow an Al y Ga 1-y N barrier layer on the surface of the template layer;

[0018] S2. MOCVD - grow an Al y Ga 1-y N native layer with a rough surface on the surface of the Al z Ga 1-z N barrier layer obtained in step S1;

[0019] S3. Keep the N source flowing in, stop flowing in the Ga source and the Al source, and cause in - situ desorption of Ga and Al atoms in the Al z Ga 1-z N native layer obtained in step S2 to obtain discrete Al x Ga 1-x N dot - like structures;

[0020] S4. Repeat steps S1 - S3 to obtain the periodic - structured AlGaN - based ultraviolet light - emitting quantum dot structure.

[0021] In step S1, the template layer is Alm Ga 1-m AlGaN template layer, where 0 < m ≤ 1; when m = 1, the template layer is an AlN template layer.

[0022] In step S1, the Al y Ga 1-y The growth conditions of the AlGaN barrier layer are: the temperature is 1000 - 1150 °C, preferably 1050 - 1110 °C.

[0023] In step S2, the Al z Ga 1-z In the AlGaN native layer, the value range of z is 0.1 - 0.7. The Al composition z of the native layer is determined according to the Al x Ga 1-x Al composition x requirement in the AlGaN quantum dots. Since the bond energy of Ga-N is lower than that of Al-N, it makes the surface Ga atoms easier to desorb, which means that during the desorption process, the Al composition increases, that is, z < x.

[0024] In step S2, the Al z Ga 1-z The thickness of the AlGaN native layer is 1.5 - 5 nm, preferably 2 - 3 nm, and the surface roughness (calculated based on a 30×30 μm 2 area) is 1 - 8 nm, preferably 2 - 6 nm.

[0025] In step S2, the Al z Ga 1-z The growth conditions of the AlGaN native layer are: the temperature is 1000 - 1150 °C, preferably 1050 - 1110 °C.

[0026] In step S3, the stopping time is 10 - 300 s, which can be specifically adjusted according to the composition requirements of the Al x Ga 1-x AlGaN quantum dots and the initial thickness of the Al z Ga 1-z AlGaN native layer to ensure that the Ga and Al atoms in this layer fully participate in the desorption process, and finally only discrete Al x Ga 1-x AlGaN dot structures remain.

[0027] In step S4, the number of repetitions is 4 - 6 times.

[0028] According to the embodiments of the present invention, the method for preparing the AlGaN-based light-emitting quantum dot structure includes the following steps:

[0029] Step 1: Simultaneously introduce a Ga source, an Al source, and an N source into the MOCVD reaction chamber. By adjusting the molar ratio of the Ga source and the Al source, on the Al m Ga1-m The Al is grown on the surface of the N template layer. y Ga 1-y N barrier layer;

[0030] Step 2: Adjust the flow rates and molar ratios of the Ga source, Al source, and N source, and grow the Al y Ga 1-y N barrier layer to obtain the Al z Ga 1-z N native layer;

[0031] Step 3: Keep the N source flowing, stop introducing the Ga source and Al source into the MOCVD reaction chamber, and perform in-situ desorption of Ga and Al atoms to obtain discrete Al x Ga 1-x N dot structures (x < y);

[0032] Step 4: Repeat Steps 1 - 3 to obtain the AlGaN-based ultraviolet light-emitting quantum dot structure with a periodic structure of Al y Ga 1-y N / Al x Ga 1-x N quantum dots.

[0033] In Steps 1 and 2, the Ga source is trimethylgallium (TMGa) or triethylgallium (TEGa), the Al source is trimethylaluminum (TMAl), and the N source is ammonia (NH3).

[0034] In a third aspect, the present invention further provides an AlGaN-based ultraviolet optoelectronic device, including the above-mentioned AlGaN-based ultraviolet light-emitting quantum dot structure.

[0035] The beneficial effects achieved by the present invention are as follows:

[0036] The present invention focuses on precisely regulating the atomic desorption behavior during the MOCVD growth process, stably realizing the AlGaN-based ultraviolet light-emitting quantum dot structure, and using this as the active region to fabricate an AlGaN-based UV-LED device.

[0037] Through the quantum dot structure, the present invention regulates the energy levels of each sub-band in the valence band, highlights the proportion of the heavy hole band in the carrier radiative recombination, effectively improves the emission polarization degree, and further improves the light extraction efficiency of the UV-LED; at the same time, it strengthens the carrier spatial confinement, enhances the overlap of the electron and hole wave functions, and improves the internal quantum efficiency of the device. Combining the above two advantages, the electro-optical conversion efficiency of the UV-LED device is ultimately improved.

[0038] The preparation method of the AlGaN-based ultraviolet light-emitting quantum dot structure of the present invention has the characteristics of high efficiency, good repeatability, and being applicable to epitaxial growth of various sizes, and is suitable for being vigorously promoted to the industrial application of ultraviolet optoelectronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a process flow chart of the preparation method of the AlGaN-based ultraviolet light-emitting quantum dot structure of the present invention.

[0040] In the figure: t1 + t2 + t3 + t4 is the total time of one cycle, and t1 is the growth time of the Al y Ga 1-y N barrier layer; t2 is the time when the Ga, Al, and N sources are switched from the barrier layer flow rate to the native layer flow rate. During this time period, the Ga and Al sources are not introduced into the MOCVD reaction chamber, and this time is relatively short, with a typical time of 3 - 5 s; t3 is the growth time of the Al z Ga 1-z N native layer; t4 is the desorption time, and the Ga and Al sources are not introduced into the MOCVD reaction chamber.

[0041] Figure 2 It is a comparison diagram of the luminescence polarization degrees of the samples prepared in Example 1 and Comparative Example 1; in the figure: the left figure is Example 1, and the right figure is Comparative Example 1.

[0042] Figure 3 It is a comparison diagram of the internal quantum efficiencies of the samples prepared in Example 1 and Comparative Example 1; in the figure: the left figure is Example 1, and the right figure is Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0044] The experimental methods used in the following embodiments are all conventional methods unless otherwise specified.

[0045] The reagents, materials, instruments, etc. used in the following embodiments can be obtained from commercial channels unless otherwise specified.

[0046] The preparation method of the AlGaN-based ultraviolet light-emitting quantum dot structure provided by the present invention specifically includes the following steps:

[0047] S1: Use MOCVD to prepare an AlN template layer or an Al m Ga 1-m N template layer for subsequent growth;

[0048] First, grow an AlN nucleation layer on the substrate, and then grow an AlN template layer or an Al m Ga 1-mThe N template layer serves as the template structure for the AlGaN-based ultraviolet multi-quantum dot structure;

[0049] To realize the AlGaN-based ultraviolet light-emitting quantum dot structure, the specific steps are as shown in S2 - S5;

[0050] S2: Adjust the growth temperature, introduce trimethylgallium (TMGa), trimethylaluminum (TMAl), and ammonia (NH3) into the reaction chamber, and grow a certain thickness of Al y Ga 1-y GaN barrier layer on the surface of the template layer; the component y can be controlled by adjusting the molar flow ratio of TMGa and TMAl, and the grown thickness can be controlled by the time t1;

[0051] S3: Adjust the molar flow rate and ratio of TMGa, TMAl, and NH3 within the time t2, and grow a certain thickness and rough-surfaced Al y Ga 1-y GaN native layer on the surface of the AlGaN barrier layer; the surface roughness can be controlled by adjusting the molar flow rate of TMGa, TMAl, and NH3, the component can be controlled by adjusting the molar flow ratio of TMGa and TMAl, and the grown thickness can be controlled by the time t3; z Ga 1-z N native layer; the surface roughness can be controlled by adjusting the molar flow rate of TMGa, TMAl, and NH3, the component can be controlled by adjusting the molar flow ratio of TMGa and TMAl, and the grown thickness can be controlled by the time t3;

[0052] S4: Keep the temperature unchanged, keep NH3 introduced into the reaction chamber, and suspend the supply of TMGa and TMAl for a suspension time of t4, so that the Ga and Al atoms in the AlGaN native layer are fully desorbed and thinned, and finally discrete Al z Ga 1-z GaN dot structures (z < x < y) are left; their components and sizes can be controlled by the cooperation of the time t4, the components, and the thickness of the AlGaN native layer; x Ga 1-x N dot structures (z < x < y); their components and sizes can be controlled by the cooperation of the time t4, the components, and the thickness of the AlGaN native layer; z Ga 1-z N native layer;

[0053] S5: Repeat steps S2 - S4 multiple times as needed to realize the AlGaN / AlGaN (x < y) quantum dot structure. x Ga 1-x N / Al y Ga 1-y N (x < y) quantum dot structure.

[0054] Example 1. Preparation of the AlGaN-based quantum dot structure with an emission wavelength of 280 nm

[0055] This example provides a method for preparing an AlGaN-based quantum dot structure with an emission wavelength of 280 nm, and the specific steps are as follows:

[0056] S1: Place a sapphire substrate with a 2-inch (0001) plane in the reaction chamber of an MOCVD equipment (3×2” Aixtron CCS FP-MOCVD), introduce H2, set the reaction chamber pressure to 60 mbar, and perform in-situ treatment at 1100 °C for 600 seconds; cool the reaction chamber to 930 °C, introduce NH3 and TMAl, and grow an AlN nucleation layer on the surface of the sapphire substrate; heat the reaction chamber to 1250 °C, introduce NH3 and TMAl, and grow an AlN template layer on the surface of the obtained AlN nucleation layer, with a thickness of 1 μm; cool the reaction chamber to 1100 °C, introduce NH3, TMAl, and TMGa, and grow an AlGaN template layer with an Al composition of 0.6 on the surface of the obtained AlN template layer, with a thickness of 600 nm; 0.6 Ga 0.4 N template layer, with a thickness of 600 nm;

[0057] S2: Control the reaction chamber temperature at 1060 °C, introduce NH3, TMAl, and TMGa, control the molar flow rate of TMGa + TMAl to be 60 μmol / min, the molar ratio of TMAl / (TMGa + TMAl) to be 20%, and the molar ratio of NH3 / (TMGa + TMAl) to be 1000, and grow an AlGaN barrier layer with an Al composition of 0.55 on the surface of the AlGaN template layer obtained in step S1, with a thickness of 10 nm; 0.6 Ga 0.4 N template layer, with a thickness of 600 nm; 0.55 Ga 0.45 N barrier layer, with a thickness of 10 nm;

[0058] S3: Adjust the molar flow rate of the organometallic source TMGa + TMAl to 200 μmol / min, the molar ratio of TMAl / (TMGa + TMAl) to 5%, and at the same time adjust the NH3 flow rate so that the molar ratio of NH3 / (TMGa + TMAl) is 1000, and grow an AlGaN native layer with an Al composition of 0.2 on the surface of the AlGaN barrier layer obtained in step S2, with a thickness of 2 nm, and the surface roughness within the range of 30×30 μm is 2 nm; 0.55 Ga 0.45 N native layer, with a thickness of 2 nm, and the surface roughness within the range of 30×30 μm is 2 nm; 0.2 Ga 0.8 N native layer, with a thickness of 2 nm, and the surface roughness within the range of 30×30 μm is 2 nm; 2 range is 2 nm;

[0059] S4: Keep NH3 introduced into the reaction chamber, suspend the supply of TMAl and TMGa for 100 seconds, so that Ga and Al atoms in the AlGaN native layer obtained in step S3 are fully desorbed and thinned, and finally leave discrete AlGaN quantum dots with a size of 100 nm, and the Al composition is 0.35; 0.2 Ga 0.8 N native layer, with a thickness of 2 nm, and the surface roughness within the range of 30×30 μm is 2 nm; 0.35 Ga 0.65 N quantum dots, with an Al composition of 0.35;

[0060] S5: Repeat steps S2 - S4 five times to obtain an AlGaN-based ultraviolet light-emitting quantum dot structure with a (Al 0.35 Ga 0.65 N / Al 0.55 Ga 0.45 N) periodic structure and a luminescence wavelength of 280 nm.

[0061] Comparative Example 1: Preparation of an AlGaN-based quantum well structure with a luminescence wavelength of 280 nm

[0062] This comparative example provides a method for preparing an AlGaN-based quantum well structure with a luminescence wavelength of 280 nm. The specific steps are as follows:

[0063] S1: Place a 2-inch (0001) face sapphire substrate in the reaction chamber of an MOCVD device (3×2” Aixtron CCS FP-MOCVD), introduce H2, and set the reaction chamber pressure to 60 mbar. Perform in-situ treatment at 1100 °C for 600 seconds. Cool the reaction chamber to 930 °C, and introduce NH3 and TMAl to grow an AlN nucleation layer. Heat the reaction chamber to 1250 °C, and introduce NH3 and TMAl to grow an AlN template layer with a thickness of 1 μm. Then cool the reaction chamber to 1100 °C, and introduce NH3, TMAl, and TMGa to grow an AlGaN template layer with an Al composition of 0.6 and a thickness of 600 nm; 0.6 Ga 0.4 N template layer, with a thickness of 600 nm;

[0064] S2: Heat the reaction chamber to 1060 °C, introduce NH3, TMAl, and TMGa, control the molar flow rate of TMGa + TMAl to be 60 μmol / min, the molar ratio of TMAl / (TMGa + TMAl) to be 20%, and the molar ratio of NH3 / (TMGa + TMAl) to be 1000, and grow an AlGaN barrier layer with an Al composition of 0.55 and a thickness of 10 nm; 0.55 Ga 0.45 N barrier layer, with a thickness of 10 nm;

[0065] S3: This treatment is different from that in Example 1. Specifically, keep the molar flow rates of the organometallic sources (TMGa + TMAl) and NH3 unchanged, adjust the molar ratio of TMAl / (TMGa + TMAl) to be 13%, and grow an AlGaN well layer with an Al composition of 0.35 and a thickness of 2 nm; 0.35 Ga 0.65 Well layer, with a thickness of 2 nm;

[0066] S4: Repeat steps S2 - S3 five times to obtain an AlGaN-based ultraviolet light-emitting quantum well structure with a luminescence wavelength of 280 nm.

[0067] Effect verification

[0068] The AlGaN-based ultraviolet light-emitting quantum dot structure with an emission wavelength of 280 nm obtained in Example 1 and the AlGaN-based ultraviolet light-emitting quantum well structure with an emission wavelength of 280 nm obtained in Comparative Example 1 were tested according to the commonly used detection methods in the art, and the results are as follows:

[0069] (1) Luminescence polarization degree

[0070] Tested by polarized photoluminescence spectroscopy. The calculation formula for the luminescence polarization degree is: ρ = (I TE -I TM ) / (I TE +I TM ), where I TE , I TM are the luminescence intensities of the TE mode and the TM mode, respectively.

[0071] As Figure 2 shown, the test results indicate that the luminescence polarization degree of the AlGaN-based ultraviolet light-emitting quantum dot structure obtained in Example 1 is 0.61, and the luminescence polarization degree of the AlGaN-based ultraviolet light-emitting quantum well structure obtained in Comparative Example 1 is 0.28. Thus, it shows that the luminescence polarization degree of the device can be significantly improved through the quantum dot structure.

[0072] (2) Internal quantum efficiency

[0073] Tested by variable-temperature photoluminescence spectroscopy. The calculation formula for the internal quantum efficiency is: IQE = I 300K / I 10K , where I 300K , I 10K are the photoluminescence intensities at the test temperatures of 300 K and 10 K, respectively.

[0074] As Figure 3 shown, the test results indicate that the internal quantum efficiency of the AlGaN-based quantum dot structure obtained in Example 1 is 76.8%, and the internal quantum efficiency of the AlGaN-based quantum well structure obtained in Comparative Example 1 is 51.7%. Thus, it shows that the internal quantum efficiency of the device can be significantly improved through the quantum dot structure.

[0075] 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 AlGaN-based ultraviolet light-emitting quantum dot structure, comprising a periodic structure; The periodic structure consists of Al x Ga 1-x N quantum dots and Al y Ga 1-y N barrier layers; Among them, 0.2 ≤ x ≤ 0.8, 0.3 ≤ y ≤ 1, y = x + b, b ≥ 0.

1.

2. The AlGaN-based ultraviolet light-emitting quantum dot structure according to claim 1, wherein: The Al y Ga 1-y N barrier layer has a thickness of 2-20 nm.

3. The AlGaN-based ultraviolet light-emitting quantum dot structure according to claim 1 or 2, characterized in that: The Al x Ga 1-x N quantum dots have a size range of 20 - 300 nm.

4. The AlGaN-based ultraviolet light-emitting quantum dot structure according to any one of claims 1-3, characterized in that: The AlGaN-based ultraviolet light-emitting quantum dot structure from bottom to top includes: A substrate; Al m Ga 1-m N template layer, 0 < m ≤ 1; Al y Ga 1-y N barrier layer, 0.3 ≤ y ≤ 1, y = x + b, b ≥ 0.1; Al x Ga 1-x N dot structures, 0.2 ≤ x ≤ 0.

8.

5. The method for preparing the AlGaN-based ultraviolet light-emitting quantum dot structure according to any one of claims 1-4, comprising the following steps: S1. Grow an Al y Ga 1-y N barrier layer on the surface of the template layer; S2. On the surface of the AlGaN barrier layer obtained in step S1, grow an AlGaN native layer with a rough surface by MOCVD; y Ga 1-y On the surface of the AlGaN barrier layer obtained in step S1, grow an AlGaN native layer with a rough surface by MOCVD; z Ga 1-z N native layer; S3. Keep the N source flowing in, stop flowing in the Ga source and the Al source, and make the Al obtained in step S2 z Ga 1-z In-situ desorption of Ga and Al atoms in the N native layer to obtain discrete Al x Ga 1-x N dot structures; S4. Repeat steps S1-S3 to obtain the AlGaN-based ultraviolet light-emitting quantum dot structure with a periodic structure.

6. The preparation method of the AlGaN-based ultraviolet light-emitting quantum dot structure according to claim 5, characterized in that: In step S1: The template layer is Al m Ga 1-m N template layer, where 0 < m ≤ 1; The Al y Ga 1-y growth conditions of the N barrier layer are as follows: the temperature is 1000 - 1150 °C.

7. The preparation method of the AlGaN-based ultraviolet light-emitting quantum dot structure according to claim 5 or 6, characterized in that: In step S2: The Al z Ga 1-z In the N native layer, the value range of z is 0.1 - 0.7, and z < x; The Al z Ga 1-z The thickness of the N native layer is 1.5 - 5 nm, and the surface roughness is 1 - 8 nm; The Al z Ga 1-z The growth temperature of the N native layer is 1000 - 1150 °C.

8. The preparation method of the AlGaN-based ultraviolet light-emitting quantum dot structure according to any one of claims 5-7, characterized in that: In step S3, the stopping time is 10 - 300 s.

9. The preparation method of the AlGaN-based ultraviolet light-emitting quantum dot structure according to any one of claims 5-8, characterized in that: In step S4, the number of repetitions is 4 - 6 times.

10. An AlGaN-based optoelectronic device, comprising the AlGaN-based ultraviolet light-emitting quantum dot structure according to any one of claims 1-4.

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