High-modulation-bandwidth high-heat-dissipation mini deep ultraviolet LED and preparation method thereof

Abstract

The application provides a high-modulation-bandwidth high-heat-dissipation MINI deep ultraviolet LED and a preparation method thereof. The LED comprises, in sequence, a buffer layer, a distributed Bragg reflector structure, an epitaxial structure, a p-type electrode and a filling metal layer, which are sequentially grown on a substrate. The substrate is thinned and etched to form a plurality of columnar through holes. The filling metal layer has a platform and a plurality of metal columns distributed on the platform. The metal columns are located in the columnar through holes. The distributed Bragg reflector structure is used to increase the light emission efficiency. The lattice-matched multi-quantum well layer is used to effectively reduce the quantum confinement Stark effect, increase the internal quantum efficiency, and greatly improve the reliability and stability of the product. The device obtained by the preparation method has higher crystal quality, more uniform light emission, better heat dissipation performance, smaller time constant and smaller carrier lifetime due to the small size of the device, improved modulation bandwidth, and enhanced application in solar-blind ultraviolet communication.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor and manufacturing thereof, and in particular to a preparation method of a high-modulation-bandwidth high-heat-dissipation MINI deep ultraviolet LED. BACKGROUND

[0002] The ultraviolet band of invisible light is divided into UVA, UVB and UVC bands, and the wavelengths are 320-420 nm, 280-320 nm and 200-280 nm, respectively. Among them, the light in the 200-280 nm UVC band cannot reach the ground due to the absorption of atmospheric ozone and is called solar blind ultraviolet light. The light communication mode using solar blind ultraviolet light communication is called solar blind ultraviolet communication, which can be used in fields such as ignoring background noise, non-line-of-sight communication and military tactical communication, and has better directivity, capture and tracking accuracy. However, the current solar blind communication still has a series of problems such as high power consumption, large size and low modulation bandwidth, and cannot be widely applied.

[0003] MINI LED refers to an LED device with a size less than 200 μm. Since the current spreading effect is better than that of large-size LED, as the size of LED decreases, the lateral propagation of LED light beam decreases, and higher luminous efficiency can be obtained. The horizontal resistance is reduced, and the current distribution is reasonably improved, greatly improving the current spreading effect. Due to its small resistance-capacitance constant (RC constant), high current density and short carrier lifetime, it can be used to prepare high-modulation-bandwidth ultraviolet communication equipment. However, due to the influence of non-radiative recombination, the light output power LOP of the current horizontal MINI LED is very small, less than 1 mW, and the wall plug efficiency WPE is less than 1%, which cannot meet the requirements of long transmission distance. Therefore, it is necessary to consider increasing the light extraction efficiency of MINI LED, better light extraction and current spreading. The heat generated by MINI LED under high current density will increase the junction temperature, and the quantum confinement Stark effect (QCSE) caused by the polarization effect in the quantum well will cause the device to appear red shift phenomenon, affecting the practical application of solar blind ultraviolet communication. SUMMARY

[0004] In view of the technical problems in the prior art, the primary object of the present application is to provide a MINI deep ultraviolet LED with high light extraction efficiency, good lattice matching, good heat dissipation performance, strong conductivity, high internal and external quantum efficiency and good overall performance, and a preparation method thereof. Based on this object, the present application at least provides the following technical solutions:

[0005] A preparation method of a high-modulation-bandwidth high-heat-dissipation MINI deep ultraviolet LED, comprising the following steps:

[0006] The buffer layer, the DBR layer, the n-type AlGaN layer, the quaternary AlInGaN / AlInGaN multi-quantum well layer, the AlGaN electron blocking layer and the p-type AlGaN / AlGaN superlattice ohmic contact layer are sequentially epitaxially grown on the substrate; the p-type electrode is prepared on the superlattice ohmic contact layer; the substrate is thinned, and then the substrate is etched to form the array structure of the columnar through holes arranged at intervals; the adhesion layer and the seed layer are sequentially deposited on the substrate and in the array structure of the columnar through holes, and then the metal electrode layer is deposited to form the filling metal layer, and finally the n-type electrode is formed.

[0007] The application further provides a high-modulation-bandwidth high-heat-dissipation MINI type deep ultraviolet LED, which comprises a filling metal layer, a substrate, a buffer layer, a DBR layer, an n-type AlGaN layer, a quaternary AlInGaN / AlInGaN multi-quantum well layer, an AlGaN electron blocking layer and a p-type AlGaN / AlGaN superlattice ohmic contact layer which are sequentially arranged on the sapphire substrate, and a p-type electrode which is arranged on the superlattice ohmic contact layer.

[0008] Further, the quaternary AlInGaN / AlInGaN multi-quantum well layer has 5 periods, wherein the lattice mismatch degree of the AlInGaN well layer and the AlInGaN barrier layer is less than 0.01.

[0009] Further, the quantum barrier AlInGaN layer has a thickness of 10-12 nm, the content of Al component is 0.6-0.8, and the content of In component is 0.14-0.22; the quantum well AlInGaN layer has a thickness of 2-4 nm, the content of Al component is 0.5, and the content of In component is 0.16.

[0010] Further, the DBR layer is composed of 20 periods of AlN / Al 0.55 Ga 0.45 N, wherein the thickness of the AlN layer is 40 nm, and the thickness of the Al 0.55 Ga 0.45 N layer is 25 nm.

[0011] Further, in the n-type AlGaN layer, the content of Al component is 0.6, the doping concentration is 1x10 18 ~1x10 19 cm -3 , and the thickness is 500 nm-1 mu m.

[0012] Further, in the AlGaN electron blocking layer, the content of Al component is 0.7, the doping concentration is 4x10 19cm -3 The thickness of the AlGaN layer is 50 nm.

[0013] Further, the p-type AlGaN / AlGaN superlattice ohmic contact layer is composed of 10 periods of Al 0.4 Ga 0.6 N / Al 0.7 Ga 0.3 N, and the thickness of the single AlGaN layer is 1 nm.

[0014] Further, the filling metal layer comprises a laminated adhesion layer, a seed layer and a metal electrode layer, the adhesion layer is selected from at least one of Ti, TiN, Ta and TaN, and the seed layer is selected from Cu.

[0015] Further, the adhesion layer is close to the buffer layer, and the buffer layer comprises a low-temperature GaN layer grown on a substrate and a high-temperature GaN layer grown on the low-temperature GaN layer.

[0016] The substrate is selected from a sapphire substrate or a silicon carbide substrate.

[0017] The present application has at least the following beneficial effects:

[0018] Compared with the conventional horizontal structure MINI LED, the MINI LED of the present application obtains greater current expansion effect and smaller lateral resistance for solar blind ultraviolet communication. The main factors affecting the LED modulation bandwidth are RC time constant and output optical power. The smaller the RC time constant is, the larger the modulation bandwidth is, and the signal is easier to be detected by the detector, which is more conducive to signal transmission. The relationship between optical power and current can be expressed as the modulation depth of the LED which can be expressed as the ratio of peak current to bias current. The MINI LED can obtain greater light-emitting efficiency due to the reduction of its size and resistance, increase the optical output power, and further obtain greater modulation depth.

[0019] The use of the Bragg mirror structure in the MINI LED structure of the present application alleviates the lattice mismatch and thermal adaptation problems between the substrate and the n-type AlGaN layer, reduces non-radiative recombination, and makes the light emitted by the active region emit in the direction of the p-type electrode through multi-layer reflection, thereby improving the light emission efficiency. In addition, the etched substrate and the filling metal layer are combined to form a structure in which the substrate and the filling metal are distributed in intervals, thereby improving the heat dissipation performance of the chip and enhancing the conductivity of the device. The current spreading property of the vertical MINI LED structure is superior to that of the small-size horizontal MINI LED structure, a larger external quantum efficiency EQE is obtained than the conventional horizontal MINI LED, and the p-AlGaN / AlGaN superlattice ohmic contact layer replaces the traditional p-type GaN ohmic contact layer, thereby avoiding the absorption of light by the p-type GaN and increasing the hole injection efficiency of the LED. In addition, the AlInGaN / AlInGaN four-element lattice matching is used in the selection of the barrier layer and the well layer of the multi-quantum well, the lattice constants of the well layer and the barrier layer material are close, the polarization between the two materials is greatly reduced, the quantum confinement Stark effect (QCSE) is reduced, the electron and hole wave function overlap rate is increased, the internal quantum efficiency is further increased, and the material red shift phenomenon is effectively improved. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A preparation flowchart of the MINI deep ultraviolet LED according to an embodiment of the present application.

[0021] Figure 2 A device structure schematic diagram of the MINI deep ultraviolet LED according to an embodiment of the present application.

[0022] Figure 3 A device structure light emission schematic diagram of the MINI deep ultraviolet LED according to an embodiment of the present application.

[0023] Figure 4 A lattice matching diagram of the four-element multi-quantum well material of the MINI deep ultraviolet LED according to an embodiment of the present application. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings of the present application. The described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application. In the following embodiments, the experimental methods are conventional methods unless otherwise specified, and the reagents and materials can be obtained from public commercial channels unless otherwise specified.

[0025] This specification uses spatially relative terms such as “below,” “under,” “down,” “above,” “above,” and “upper” to explain the positioning of one element relative to a second element. These terms are intended to cover different orientations of the device, except for those different from those shown in the figures.

[0026] Furthermore, the use of terms such as "first" and "second" to describe various elements, layers, regions, and sections is not intended to be restrictive. The use of terms such as "having," "containing," "including," and "comprises" are open-ended terms, indicating the presence of the stated elements or features, but not excluding additional elements or features, unless the context explicitly states otherwise.

[0027] One embodiment of the present invention provides a high-modulation-bandwidth heat dissipation MINI deep ultraviolet LED, such as... Figure 2 The structure includes a substrate 1, a filler metal layer 2, a buffer layer 3 sequentially stacked on the substrate 1 and the filler metal layer 2, a distributed Bragg reflector (DBR) layer 4, an n-type AlGaN layer 5, a quaternary AlInGaN / AlInGaN multiple quantum well layer 6, an AlGaN electron blocking layer 7, a p-type AlGaN / AlGaN superlattice ohmic contact layer 8, and a p-type electrode 9.

[0028] Substrate 1 is selected from either a sapphire substrate or a silicon carbide substrate; in this preferred embodiment, a sapphire substrate is selected. The filling metal layer is composed of an adhesive layer, a seed layer, and a metal electrode layer stacked sequentially, as follows: Figure 2 As shown, the filling metal layer includes a platform and an array of metal pillars arranged on the platform, with the substrate 1 disposed between the metal pillars. An adhesive layer is located close to the substrate 1. In one embodiment, a plurality of arrayed columnar holes are etched along the back side of the substrate 1, and an adhesive layer, a seed layer, and a metal electrode layer are sequentially deposited to fill the columnar holes to form the filling metal layer. Because sapphire substrates have poor thermal conductivity, compared to a whole sapphire substrate, the columnar holes formed by this etching are filled with a metal layer, which improves the heat dissipation performance of the chip and enhances the conductivity of the device.

[0029] The buffer layer 3 is composed of a low-temperature GaN layer and a high-temperature GaN layer stacked together, with the low-temperature GaN layer in contact with the substrate 1. The thickness of the low-temperature GaN layer is 50 nm, and the thickness of the high-temperature GaN layer is 100 nm.

[0030] The distributed Bragg reflector (DBR) layer 4 consists of 20 pairs of alternating AlN / Al layers. 0.55 Ga 0.45 It consists of N layers, where the AlN layer is 40 nm thick. 0.55 Ga 0.45 The thickness of the N-layer is 25 nm. This Bragg reflector DBR layer reflects light towards the p-type electrode, increasing the light extraction efficiency.

[0031] In the n-type AlGaN layer 5, the Al content is 0.6%, and the doping concentration is 1×10⁻⁶. 18 ~1×10 19 cm -3 Its thickness is 500nm to 1μm, and its doping type is Si doping.

[0032] The Al and In composition of the quaternary AlInGaN / AlInGaN multiple quantum well (MQW) layer 6 is selected as follows: Figure 4 As shown, this illustrates the quaternary lattice matching of the high-modulation-bandwidth, high-heat-dissipation MINI deep ultraviolet LED obtained in this invention. This quaternary lattice matching method controls the wavelength to 254 nm. The AlInGaN quantum well uses an Al composition of 0.5% and an In composition of 0.16%, with a bandgap of 4.03 eV and a lattice constant of 0.3206 nm. Quantum barrier data matching its lattice constant are shown below. Figure 4 As shown, with Al content as the x-axis and In content as the y-axis, the points on the image represent points where the lattice constant matches the quantum well. Points with Al content in the range of 0.6–0.8 and In content in the range of 0.14–0.22 have lattice constants close to those of the quantum well. For example, in an AlInGaN quantum barrier, an Al content of 0.7 and an In content of 0.18 are selected, resulting in a bandgap of 4.52 eV, which is greater than that of the quantum well, and a lattice constant of 0.3198 nm. The lattice mismatch between the well layer and the barrier layer is less than 0.01, which greatly reduces the quantum confinement Stark effect, effectively improves the redshift of the material, and increases the wavefunction overlap rate of electrons and holes in the active region, thereby increasing the internal quantum efficiency (IQE) and increasing the optical output power.

[0033] In the AlGaN electron blocking layer (EBL) 7, the Al content is 0.7%, the doping type is Mg doping, and the doping concentration is 4×10⁻⁶. 19 cm -3 Its thickness is 50nm.

[0034] The p-type AlGaN / AlGaN superlattice ohmic contact layer consists of 10 periods of Al 0.4 Ga 0.6 N / Al 0.7 Ga 0.3 The superlattice is composed of alternating N layers, with each monolayer of AlGaN having a thickness of 1 nm. This superlattice ohmic contact layer avoids the light absorption of p-GaN caused by conventional structures, and the high Mg impurity concentration of the superlattice structure improves the hole injection efficiency of the LED.

[0035] A p-type electrode 9 is disposed on the superlattice ohmic contact layer 8, and the p-type electrode 9 is, for example, a Ni / Au electrode, the thickness of the Ni layer being 20 nm and the thickness of the Au layer being 50 nm.

[0036] Another embodiment of the present application provides a method for manufacturing the above-mentioned deep ultraviolet LED, which comprises the following steps: Figure 1 As shown in the figure, the method comprises the following steps:

[0037] First, a sapphire substrate is prepared, and a buffer layer is grown on the sapphire substrate by using a MOCVD process. The temperature of the chamber is set to 1150°C, the sapphire substrate is heat-treated in an H2 atmosphere, then trimethyl gallium (TMGa) is used as a gallium source, NH3 is used as a nitrogen source, and H2 or N2 is used as a carrier gas, the temperature is reduced to 550°C, a 50-nm-thick low-temperature GaN layer is grown at low temperature, then the temperature is increased to 1100°C, a 100-nm-thick high-temperature GaN layer is grown on the low-temperature GaN layer, and the GaN layer is recrystallized;

[0038] Then, a distributed Bragg reflector (DBR) layer is grown on the buffer layer, 20 periods of AlN / Al 0.55 Ga 0.45 N layer structures are grown at 1100°C, the thickness of the AlN layer is 40 nm, and the thickness of the Al 0.55 Ga 0.45 N layer is 25 nm.

[0039] Next, an n-type AlGaN layer with a thickness of 500 nm, 5 pairs of quaternary AlInGaN / AlInGaN multi-quantum well layers, an AlGaN electron blocking layer with a thickness of 50 nm, and 10 pairs of periodically arranged Al 0.4 Ga 0.6 N / Al 0.7 Ga 0.3 N superlattice ohmic contact layers are sequentially grown on the DBR layer. In the quaternary AlInGaN / AlInGaN multi-quantum well layers, the Al composition of the well layer in a single period is selected to be 0.5, the In composition is selected to be 0.16, the band gap is 4.03 eV, the lattice constant is 0.3206 nm, the Al composition of the barrier layer is selected to be 0.7, the In composition is selected to be 0.18, the band gap is 4.52 eV, which is greater than the band gap of the quantum well, the lattice constant is 0.3198 nm, and the lattice mismatch degree of the well layer and the barrier layer is less than 0.01. In the Al 0.4 Ga 0.6 N / Al 0.7 Ga 0.3 N superlattice ohmic contact layer, the thickness of each AlGaN layer is 1 nm.

[0040] Then, a p-type electrode is prepared. A Ni / Au double-layer metal is prepared on the superlattice ohmic contact layer, the thickness of the Ni layer is 20 nm, the thickness of the Au layer is 50 nm, and then annealing is performed at a temperature of 600 DEG C for 90 s in a mixed gas of N2 and O2, the volume ratio of N2 and O2 being 4:1.

[0041] Then, the sapphire substrate is thinned. The above epitaxial wafer is adhered to a flat glass with wax, fixed on a grinding clamp, and the back surface of the sapphire substrate is thinned by mechanical grinding at a speed of 800-1200 r / min, and the sapphire substrate is thinned to 100 mu m, and then a chemical mechanical polishing process is used to remove the damage layer caused by mechanical grinding, and the back surface of the thinned sapphire substrate is polished at room temperature using an alkaline SiO2 suspension with a pH of about 10-13, the grinding particle size is set to 120 nm, and the grinding rate is set to 500 nm / min.

[0042] Then, the sapphire substrate is etched. The above epitaxial wafer is washed in anhydrous ethanol and deionized water for 5 min, and the above sapphire substrate is etched by infrared femtosecond laser, the laser pulse width of the infrared femtosecond laser is set to 0.4-6 ps, and the frequency is set to 25-500 kHz, the sapphire substrate is etched to form an array of columnar through holes, the diameter of the through holes is 20-30 mu m, and the width of the substrate between adjacent through holes is 20-30 mu m, then an adhesion layer and a seed layer are sputtered in an argon atmosphere at a temperature of 100 DEG C, the chamber pressure is set to 5 mTorr, and the gas flow is set to 20 sccm. The adhesion layer is selected from at least one of Ti, TiN, Ta and TaN, and the seed layer is a Cu seed layer.

[0043] Then, a conductive metal layer is filled. A CVD process is used to deposit a conductive metal, and the conductive metal is selected from materials with high conductive performance such as copper and tungsten, which is used as the n-type electrode of the MINI LED.

[0044] The MINI LED structure obtained by the embodiment of the present application can obtain greater current expansion and smaller resistance, thereby obtaining smaller time constant and smaller carrier lifetime, increasing the modulation bandwidth of the LED, and the signal is easier to be detected by the detector, greatly enhancing the application of deep ultraviolet LED in solar blind ultraviolet communication. The current expansion property of the full-vertical MINI LED structure of the present application is better than that of the small-size horizontal MINI LED structure, and a greater external quantum efficiency EQE is obtained than the conventional horizontal MINI LED, as shown in Figure 3 The light emission uniformity and heat dissipation performance of the MINI deep ultraviolet LED of the present application are better, and the reliability and stability of the product are greatly improved.

[0045] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any changes, modifications, substitutions, combinations, simplifications, etc. made without departing from the spirit and principles of the present application should be equivalent replacement manners and should be included in the protection scope of the present application.

Claims

1. A method for fabricating a high-modulation-bandwidth, high-heat-dissipation MINI-type deep ultraviolet LED, characterized in that, Includes the following steps: A buffer layer, consisting of 20 AlN / Al cycles, was sequentially epitaxially grown on the substrate. 0.55 Ga 0.45 The structure consists of an N-type distributed Bragg reflector (DBR) layer, an n-type AlGaN layer, a quaternary AlInGaN / AlInGaN multi-quantum-well layer, an AlGaN electron blocking layer, and a p-type AlGaN / AlGaN superlattice ohmic contact layer. A p-type electrode is fabricated on the superlattice ohmic contact layer; The substrate is thinned, and then the substrate is etched to form an array of spaced columnar vias; An adhesion layer and a seed layer are sequentially deposited on the substrate and in the columnar via array structure, followed by the deposition of a metal electrode layer to form a filling metal layer, ultimately forming an n-type electrode. In the quaternary AlInGaN / AlInGaN multi-quantum-well layer, the number of periods is 5, the lattice mismatch between the well layer and the barrier layer is less than 0.01, the thickness of the barrier layer is 10~12 nm, and the content of Al component is 0.6~0.8 and the content of In component is 0.14~0.22; the thickness of the well layer is 2~4 nm, and the content of Al component is 0.5 and the content of In component is 0.

16. The thickness of the AlN layer in the distributed Bragg reflector (DBR) layer is 40 nm. 0.55 Ga 0.45 The thickness of the N layer is 25 nm; The p-type AlGaN / AlGaN superlattice ohmic contact layer consists of 10 periods of Al 0.4 Ga 0.6 N / Al 0.7 Ga 0.3 Composed of N, the thickness of a single AlGaN layer is 1 nm; The buffer layer includes a low-temperature GaN layer grown on the substrate and a high-temperature GaN layer grown on the low-temperature GaN layer.

2. A high-modulation-bandwidth, high-heat-dissipation MINI-type deep ultraviolet LED, characterized in that, Includes a filler metal layer having a platform and a plurality of metal pillars arranged in an array on the platform; Substrate, disposed between the metal pillars; Buffer layer, consisting of 20 cycles of AlN / Al 0.55 Ga 0.45 A distributed Bragg reflector (DBR) layer composed of N elements, an n-type AlGaN layer, a quaternary AlInGaN / AlInGaN multi-quantum-well layer, an AlGaN electron blocking layer, and a p-type AlGaN / AlGaN superlattice ohmic contact layer are sequentially disposed on the substrate. A p-type electrode is disposed on the superlattice ohmic contact layer; In the quaternary AlInGaN / AlInGaN multi-quantum-well layer, the number of periods is 5, the lattice mismatch between the well layer and the barrier layer is less than 0.01, the thickness of the barrier layer is 10~12 nm, and the content of Al component is 0.6~0.8 and the content of In component is 0.14~0.22; the thickness of the well layer is 2~4 nm, and the content of Al component is 0.5 and the content of In component is 0.

16. The thickness of the AlN layer in the distributed Bragg reflector (DBR) layer is 40 nm. 0.55 Ga 0.45 The thickness of the N layer is 25 nm; The p-type AlGaN / AlGaN superlattice ohmic contact layer consists of 10 periods of Al 0.4 Ga 0.6 N / Al 0.7 Ga 0.3 Composed of N, the thickness of a single AlGaN layer is 1 nm; The buffer layer includes a low-temperature GaN layer grown on a substrate and a high-temperature GaN layer grown on the low-temperature GaN layer; The filling metal layer includes a stacked adhesive layer, a seed layer, and a metal electrode layer, with the adhesive layer located close to the buffer layer.

3. The preparation method according to claim 1 or the deep ultraviolet LED according to claim 2, characterized in that, In the n-type AlGaN layer, the Al content is 0.6%, and the doping concentration is 1×10⁻⁶. 18 ~1×10 19 cm -3 Its thickness is 500nm~1μm.

4. The preparation method according to claim 1 or the deep ultraviolet LED according to claim 2, characterized in that, The AlGaN electron blocking layer has an Al content of 0.7% and a doping concentration of 4 × 10⁻⁶. 19 cm -3 Its thickness is 50nm.

5. The preparation method according to claim 1 or the deep ultraviolet LED according to claim 2, characterized in that, The adhesive layer is selected from at least one of Ti, TiN, Ta and TaN, and the seed layer is selected from Cu.

6. The preparation method according to claim 1 or the deep ultraviolet LED according to claim 2, characterized in that, The substrate is selected from sapphire substrate or silicon carbide substrate.

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