Gallium nitride-based LED epitaxial structure and preparation method thereof

Abstract

The application provides a gallium nitride-based LED epitaxial structure and a preparation method thereof, wherein the gallium nitride-based LED epitaxial structure comprises: a nucleation layer, a current spreading layer, a stress buffer layer, an InAlN electron blocking layer, a multi-quantum well barrier region, an AlGaN electron blocking layer and a P-type GaN layer which are sequentially grown on the surface of a growth substrate, wherein the InAlN electron blocking layer is composed of a multi-period InAlN / GaN structure; in each period structure, the In component in the InAlN layer is 1% to 25%. The InAlN electron blocking layer composed of the multi-period InAlN / GaN structure is inserted in front of the multi-quantum well barrier region, and the electrons are further blocked on the basis of the AlGaN electron blocking layer, so that the probability of electron escape from the multi-quantum well barrier region under the working of a super-large current of the LED chip is effectively reduced, and the light efficiency of the LED chip under the super-large current is improved.

Description

Technical Field

[0001] This invention relates to the field of LED technology, and in particular to a gallium nitride-based LED epitaxial structure and its fabrication method. Background Technology

[0002] When GaN-based LEDs are driven by operating current, some electrons injected into the multiple quantum well (MQW) region can gain enough energy to escape the MQW region through mechanisms such as electric field acceleration, multiphonon recombination, and Auger recombination, thus severely reducing the photoelectric efficiency of GaN-based LEDs under high current. To solve this problem, the industry generally adopts the method of inserting a p-type AlGaN electron blocking layer (EBL) after the MQW to reduce electron escape.

[0003] For common GaN LED applications, such as indoor lighting, mobile lighting, outdoor lighting, and TV backlighting, the chip's operating current density is generally low, typically not exceeding 100 A / cm². 2 The p-type AlGaN EBL insertion layer can effectively improve the luminous efficacy of LEDs, and therefore, the AlGaN EBL insertion layer has become the standard configuration for current GaN LED structures. However, with the expansion of GaN LED applications, some scenarios have emerged that require applying ultra-high current densities to a single LED, such as projector backlighting, high-intensity flashlights, and ultra-long-range lighting, requiring LED chips to operate at 200 A / cm². 2 Continuous operation at the above current densities. Micro LEDs used in AR displays and LiFi (Li-Fi) can even operate at current densities approaching 1000 A / cm². 2 At such ultra-high current densities, the traditional AlGaN EBL insertion layer is no longer effective at blocking current escape. Simply increasing the thickness of the AlGaN EBL insertion layer or (and) increasing the Al content in the AlGaN EBL insertion layer to enhance electron blocking will lead to difficulties in hole injection and increased operating voltage, which will also degrade the luminous efficacy of the LED device. Summary of the Invention

[0004] To overcome the above shortcomings, this invention provides a gallium nitride-based LED epitaxial structure and its fabrication method, which effectively reduces the probability of electrons escaping from the multi-quantum well barrier region when gallium nitride-based LEDs operate at ultra-high current, thereby improving luminous efficiency.

[0005] The technical solution provided by this invention is as follows:

[0006] On one hand, the present invention provides a gallium nitride-based LED epitaxial structure, comprising: a nucleation layer, a current spreading layer, a stress buffer layer, an InAlN electron blocking layer, a multiple quantum well barrier region, an AlGaN electron blocking layer, and a P-type GaN layer sequentially grown on the surface of a growth substrate, wherein the InAlN electron blocking layer is composed of multiple InAlN / GaN periodic structures; in each periodic structure, the In composition of the InAlN layer is 1% to 25%.

[0007] On the other hand, the present invention provides a method for fabricating a gallium nitride-based LED epitaxial structure, comprising: sequentially forming a nucleation layer, a current spreading layer, a stress buffer layer, an InAlN electron blocking layer, a multiple quantum well barrier region, an AlGaN electron blocking layer, and a P-type GaN layer on the surface of a growth substrate, wherein the InAlN electron blocking layer is composed of multiple InAlN / GaN periodic structures; in each periodic structure, the In composition of the InAlN layer is 1% to 25%.

[0008] In the gallium nitride-based LED epitaxial structure and its fabrication method provided by this invention, an InAlN electron blocking layer composed of multiple InAlN / GaN periodic structures is inserted in front of the multi-quantum-well barrier region. Based on the AlGaN electron blocking layer, electrons are further blocked, which can effectively reduce the probability of electrons escaping from the multi-quantum-well barrier region when the LED chip is operating at ultra-high current, thereby improving the luminous efficiency of the LED chip under ultra-high current. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the gallium nitride-based LED epitaxial structure in this invention;

[0010] Figure 2 This is a schematic diagram of the InAlN electron blocking layer structure in an example of the present invention;

[0011] Figure 3 This is a schematic diagram of the epitaxial structure of a gallium nitride-based LED in an example of the present invention.

[0012] Figure label:

[0013] 1-Growth substrate, 2-Nucleation layer, 3-Current spreading layer, 4-Stress buffer layer, 5-InAlN electron blocking layer, 6-Multiple quantum well barrier region, 7-AlGaN electron blocking layer, 8-P-type GaN layer. Detailed Implementation

[0014] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0015] This invention provides a gallium nitride-based LED epitaxial structure, such as... Figure 1 As shown, it includes: a nucleation layer 2, a current spreading layer 3, a stress buffer layer 4, an InAlN electron blocking layer 5, a multiple quantum well barrier region 6, an AlGaN electron blocking layer 7, and a P-type GaN layer 8, which are sequentially grown on the surface of the growth substrate 1. The InAlN electron blocking layer 7 is composed of multiple InAlN / GaN periodic structures; in each periodic structure, the In composition of the InAlN layer is 1% to 25%.

[0016] Specifically, the growth substrate 1 can be any substrate such as sapphire, silicon, or silicon carbide; the nucleation layer 2 is a GaN layer and / or an AlN layer and / or an AlGaN layer, with a thickness of 10 nm to 3000 nm; the current spreading layer 3 is a GaN layer or an AlGaN layer, with a thickness of 500 nm to 5000 nm; and the stress buffer layer 4 is an InGaN / GaN superlattice structure or a low-temperature GaN layer. In the InAlN electron blocking layer 5, the repetition period of InAlN / GaN is between 1 and 50, and in each periodic structure, the thickness of the InAlN layer is 1 nm to 50 nm, and the thickness of the GaN layer is 1 nm to 100 nm. In practical applications, Si doping can be selectively performed on the GaN layer, especially when the thickness of the GaN layer exceeds 4.5 nm. When the thickness is relatively thin, between 1 nm and 4.5 nm, doping may not be necessary. The multiple quantum well barrier region 6 is formed by an InGaN / GaN or InGaN / AlGaN multiple quantum well barrier structure, with a period of 1 to 10. In the InGaN / GaN multiple quantum well barrier structure, the thickness of a single InGaN quantum well is 1 nm to 5 nm, and the thickness of a single GaN quantum barrier is 3 nm to 20 nm. In the InGaN / AlGaN multiple quantum well barrier structure, the thickness of a single InGaN quantum well is 1 nm to 5 nm, and the thickness of a single AlGaN quantum barrier is 3 nm to 20 nm. The AlGaN electron blocking layer 7 has a thickness of 5 nm to 50 nm, with an Al composition not exceeding 30%. The p-type GaN layer 8 has a thickness of 50 nm to 150 nm.

[0017] Correspondingly, this invention also provides a method for fabricating a gallium nitride-based LED epitaxial structure, comprising: sequentially forming a nucleation layer, a current spreading layer, a stress buffer layer, an InAlN electron blocking layer, a multiple quantum well barrier region, an AlGaN electron blocking layer, and a P-type GaN layer on the surface of a growth substrate, wherein the InAlN electron blocking layer is composed of multiple InAlN / GaN periodic structures; in each periodic structure, the In composition of the InAlN layer is 1% to 25%. In the InAlN electron blocking layer, the repetition period of InAlN / GaN is between 1 and 50, and in each periodic structure, the thickness of the InAlN layer is 1 nm to 50 nm, and the thickness of the GaN layer is 1 nm to 100 nm.

[0018] In the above-mentioned gallium nitride-based LED epitaxial structure and the prepared gallium nitride-based LED epitaxial structure, the conduction band barrier height difference between the InAlN layer and the GaN layer in the InAlN electron blocking layer is higher than the conduction band barrier height difference between the AlGaN electron blocking layer and the GaN layer. As a result, the InAlN layer in the InAlN electron blocking layer has a strong deceleration (blocking) effect on electrons injected into the multiple quantum well barrier region (MQW), thereby effectively reducing the probability of electrons escaping from the multiple quantum well barrier region by crossing the p-type AlGaN electron blocking layer under ultra-high current.

[0019] The following example further illustrates the above-mentioned gallium nitride-based LED epitaxial structure and fabrication method:

[0020] Using an MOCVD growth apparatus, a 100mm diameter silicon (111) wafer was selected as the growth substrate 1. AlN and AlGaN layers were used as nucleation layers 2. A Si-doped GaN layer was used as the epitaxial layer 3. An InGaN / GaN superlattice structure was used as a stress buffer layer 4. Figure 2 As shown, Si-doped In 0.18 Al 0.82 The N / GaN dual-period structure serves as the InAlN electron blocking layer 5(In 0.18 Al 0.82 The reference numeral for N is 51, and the reference numeral for the GaN layer is 52. Undoped In 0.15 Ga 0.85 N / GaN as a multiple quantum well barrier 6. Mg-doped AlGaN as a pAlGaN EBL layer 7. Mg-doped GaN as a p-type GaN layer 8. Epitaxial structures such as Figure 3 As shown, the preparation process is as follows:

[0021] First, the growth substrate 1 is placed in the MOCVD reaction chamber, heated to 1100℃, and H2 is introduced to perform high-temperature surface cleaning and annealing of the growth substrate 1. The annealing time is between 2 and 10 minutes. Subsequently, the surface temperature of the growth substrate 1 is controlled between 800℃ and 1100℃, and the reaction chamber pressure is 50 Torr. Using hydrogen as a carrier gas, trimethylaluminum (TMAl) and ammonia (NH3) are introduced into the reaction chamber to grow an AlN layer with a thickness between 50 nm and 300 nm on the growth substrate 1. After the AlN layer growth is completed, the reaction chamber pressure is increased to 70 Torr, using H2 as a carrier gas, and the epitaxial wafer temperature is set to 1000℃ to 1100℃. Trimethylaluminum (TMAl), trimethylgallium (TMGa), and ammonia (NH3) are introduced into the reaction chamber to grow one AlGaN layer or multiple AlGaN layers with decreasing Al composition. The AlGaN layer thickness is between 100 nm and 700 nm. AlN and AlGaN are used together as nucleation layer 2.

[0022] Subsequently, the reaction chamber pressure was increased to 100 Torr, using a mixed carrier gas of H2 and N2, and the epitaxial wafer temperature was set to 1000℃~1100℃. Trimethylgallium (TMGa), ammonia (NH3), and silane (SiH4) were introduced into the reaction chamber to grow current-extended layer 3 (n-type GaN epitaxial layer), with a Si doping concentration of 1E19 / cm³. 3 The thickness is 3000nm.

[0023] After the current-spreading layer 3 has grown, the epitaxial wafer temperature is lowered to 850°C, and In is grown for 50 cycles. 0.05 Ga 0.95 N / GaN superlattice serves as stress buffer layer 4, where In 0.05 Ga 0.95 The thickness of a single N layer is 1.5 nm, and the thickness of a single GaN layer is 2 nm.

[0024] Then, the epitaxial wafer temperature was lowered to 800°C, the reaction chamber pressure was increased to 300 Torr, and trimethylaluminum (TMAl), trimethylindium (TMIn), ammonia (NH3), and silane (SiH4) were introduced into the reaction chamber. 0.05 Ga 0.95 In grown on N / GaN stress buffer layer 4 0.18 Al 0.82 N / GaN dual-period electron blocking layer 5, wherein In 0.18 Al 0.82 The thickness of the N monolayer is 4 nm, the thickness of the GaN monolayer is 2 nm, and the In... 0.18 Al 0.82 The N-layer is undoped, and the Si doping concentration of the GaN layer is 5E18 / cm³. 3 .

[0025] Subsequently, In grew for 9 cycles 0.15 Ga 0.85 N / GaN is used as a multi-quantum well barrier layer 6, where a single In 0.15 Ga 0.85 The thickness of an N-type quantum well is 3 nm, and the thickness of a single GaN quantum barrier is 4.5 nm.

[0026] Subsequently, trimethylgallium (TMGa), trimethylaluminum (TMAl), ammonia (NH3), and magnesium pyrocene (CP2Mg) were introduced into the reaction chamber to grow p-type Al. 0.2 Ga 0.8 N electron blocking layer 7, 35 nm thick, with Mg doping concentration of 2E19 / cm³. 3 .

[0027] Finally, in p-type Al 0.2 Ga 0.8 A 100 nm p-type GaN layer 8 is grown on top of the N-electron blocking layer 7, with a Mg doping concentration ranging from 1E18 / cm³. 3 Gradually rising to 2E20 / cm 3 .

[0028] In this epitaxial structure, the In component is 18% In. 0.18 Al 0.82 The conduction band barrier height difference between N and GaN is 1.14 eV, which is much higher than that of Al with an Al composition of 20%. 0.2 Ga 0.8 The conduction band barrier height difference between N and GaN (the conclusion applies to InAlN and AlGaN electron blocking layers with other compositions; Al composition of 30% Al) 0.3 Ga 0.7 The conduction band barrier height difference between N and GaN is 0.53 eV (the same applies), causing In in the InAlN electron blocking layer to... 0.18 Al 0.82 The N-layer has a strong deceleration (blocking) effect on electrons injected into the multiple quantum well (MQW) region, thus effectively reducing the probability of electrons escaping the MQW region by crossing the p-type AlGaN electron blocking layer under ultra-high current. Meanwhile, In... 0.18 Al 0.82 The lattice constant of N on the c-plane is the same as that of GaN. In is inserted before the multi-quantum-well-barrier region. 0.18 Al 0.82 N will not introduce additional compressive strain that would degrade the crystal quality of the upper InGaN quantum well.

[0029] It should be noted that the above embodiments can be freely combined as needed. The above description is only a preferred embodiment of the present invention. It should be pointed out that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A gallium nitride-based LED epitaxial structure, characterized in that, include: A nucleation layer, a current spreading layer, a stress buffer layer, an InAlN electron blocking layer, a multiple quantum well barrier region, an AlGaN electron blocking layer, and a P-type GaN layer are sequentially grown on the surface of a growth substrate. The InAlN electron blocking layer is composed of multiple InAlN / GaN periodic structures. In each periodic structure, the In composition of the InAlN layer is 1% to 25%. The conduction band barrier height difference between the InAlN layer and the GaN layer in the InAlN electron blocking layer is higher than the conduction band barrier height difference between the AlGaN electron blocking layer and the GaN layer.

2. The gallium nitride-based LED epitaxial structure as described in claim 1, characterized in that, In the InAlN electron blocking layer, the repetition period of InAlN / GaN is between 1 and 50, and in each periodic structure, the thickness of the InAlN layer is 1 nm to 50 nm, and the thickness of the GaN layer is 1 nm to 100 nm.

3. The gallium nitride-based LED epitaxial structure as described in claim 1 or 2, characterized in that, The growth substrate is a sapphire substrate, a silicon substrate, or a silicon carbide substrate; and / or, the nucleation layer is a GaN layer and / or an AlN layer and / or an AlGaN layer, with a thickness of 10 nm to 3000 nm.

4. The gallium nitride-based LED epitaxial structure as described in claim 1 or 2, characterized in that, The current spreading layer is a GaN layer or an AlGaN layer with a thickness of 500 nm to 5000 nm; and / or, the stress buffer layer is an InGaN / GaN superlattice structure or a porous structure.

5. The gallium nitride-based LED epitaxial structure as described in claim 1 or 2, characterized in that, The multiple quantum well barrier region is formed by an InGaN / GaN or InGaN / AlGaN multiple quantum well barrier structure, and the period of the multiple quantum well barrier structure is 1 to 10. In the InGaN / GaN multiple quantum well barrier structure, the thickness of a single InGaN quantum well is 1 nm to 5 nm, and the thickness of a single GaN quantum barrier is 3 nm to 20 nm. In the InGaN / AlGaN multiple quantum well barrier structure, the thickness of a single InGaN quantum well is 1 nm to 5 nm, and the thickness of a single AlGaN quantum barrier is 3 nm to 20 nm.

6. The gallium nitride-based LED epitaxial structure as described in claim 1 or 2, characterized in that, The thickness of the AlGaN electron blocking layer is 5nm to 100nm; and / or, the thickness of the P-type GaN layer is 50nm to 500nm.

7. A method for fabricating a gallium nitride-based LED epitaxial structure, characterized in that, include: A nucleation layer, a current spreading layer, a stress buffer layer, an InAlN electron blocking layer, a multiple quantum well barrier region, an AlGaN electron blocking layer, and a P-type GaN layer are sequentially formed on the surface of a growth substrate. The InAlN electron blocking layer is composed of multiple InAlN / GaN periodic structures. In each periodic structure, the In composition of the InAlN layer is 1% to 25%. The conduction band barrier height difference between the InAlN layer and the GaN layer in the InAlN electron blocking layer is higher than the conduction band barrier height difference between the AlGaN electron blocking layer and the GaN layer.

8. The method for fabricating a gallium nitride-based LED epitaxial structure as described in claim 7, characterized in that, In the InAlN electron blocking layer, the repetition period of InAlN / GaN is between 1 and 50, and in each periodic structure, the thickness of the InAlN layer is 1 nm to 50 nm, and the thickness of the GaN layer is 1 nm to 100 nm.

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