CN103887381B - A kind of growing method for lifting ultraviolet LED epitaxial material crystalline quality - Google Patents

Abstract

The invention is a new epitaxial method for growing ultraviolet LEDs, which can obviously improve the crystallization quality of ultraviolet LED epitaxial growth materials and enhance the luminous intensity of ultraviolet LEDs. The present invention adopts the method of gradually changing the Al composition to dope in the middle of AlN, which can gradually release the stress from the lattice adaptation of the substrate layer, and the gradual composition growth can reduce the defects of the lattice adaptation of the interface, and improve the crystal of the material interface At the same time, the gradual growth can slip dislocations, make threading dislocations segregate, well block threading dislocations from entering the quantum well region, and provide a very good substrate for growing quantum wells, and greatly reduce the The influence of the stress generated by lattice fitting on the growth of quantum wells improves the overall crystallization quality of the material, enhances the spatial overlap of the electron-hole wave function of the quantum well layer, and improves the overall optoelectronic characteristics of the UV LED.

Description

A growth method for improving the crystallization quality of ultraviolet LED epitaxy materials

technical field

The invention belongs to the field of semiconductor optoelectronics, and in particular relates to a new violet LED epitaxy method.

Background technique

With the development of LED applications, the market demand for ultraviolet LEDs is increasing. Ultraviolet LEDs with emission wavelengths covering 210-400nm have advantages that traditional ultraviolet light sources cannot match. Ultraviolet LEDs can not only be used in the field of lighting, but also can replace traditional ultraviolet mercury lamps containing toxic and harmful substances in biomedicine, anti-counterfeiting identification, air and water purification, biochemical detection, and high-density information storage. Under the current LED background , the Ziguang market prospect is very broad.

At present, the epitaxial growth technology of ultraviolet LED is not mature enough, and the material preparation for growing high-performance ultraviolet LED is difficult, and p-layer doping is difficult, and the luminous efficiency of the light-emitting area is low, which leads to the low luminous efficiency of the ultraviolet LED chip and high preparation cost. It is difficult and the yield is low.

The market potential of ultraviolet LED chips is huge, the application fields are broad, and the price is expensive. Therefore, how to prepare ultraviolet LED chips with good crystal quality and high power is an urgent problem to be solved at present.

Contents of the invention

The invention is a new epitaxial method for growing ultraviolet LEDs, which can obviously improve the crystallization quality of ultraviolet LED epitaxial growth materials and enhance the luminous intensity of ultraviolet LEDs.

Basic scheme of the present invention is as follows:

A growth method for improving the crystallization quality of ultraviolet LED epitaxial materials, comprising the following steps:

(1) Use sapphire as the growth substrate to grow the low-temperature AlN layer;

(2) Growth of high temperature AlN layer;

(3) Several cycles of ultra-thin AlGaN/AlN layers are grown. In each cycle, AlGaN is grown in a way that the Al composition first gradually decreases and then gradually increases, and then AlN is grown;

(4) Growth of n-type AlGaN layer doped with silane;

(5) AlxGa1-xN/AlGaN superlattice layers grown for several periods, x<y;

(6) AlxGa1-xN/AlyGa1-yN (y>x) quantum well barrier regions grown for several periods, x<y;

(7) Growth of p-type AlGaN barrier layer doped with magnesium;

(8) Growth of p-type AlGaN layer doped with magnesium;

(9) Growth of p-type GaN layer doped with magnesium;

(10) Under nitrogen atmosphere, anneal.

The "high temperature" and "low temperature" mentioned above are technical terms with clear meanings in this field.

Based on the above-mentioned basic scheme, the present invention also makes the following optimization limitations and improvements:

Each cycle of step (3) first grows 1-3nm in a manner of gradually decreasing Al composition, then grows 1-3nm in a manner of gradually increasing Al composition, and then grows a 3-5nm AlN thin layer.

The growth of each cycle in step (3) can be carried out as follows: at a temperature of 1060°C, turn on TMGa and TMAl, where TMAl has been kept at 40umol/min, and the flow rate of TMGa is gradually increased from 0 to 300umol/min, growing 1.5nm , and then gradually reduce the flow rate of TMGa from 300umol/min to 0, grow 1.5nm; then turn off TMGa, grow 3nm AlN thin layer.

Step (5) grows 10 cycles in total, and the thickness of each cycle is 7nm; step (6) grows 8 cycles in total, and the thicknesses of well layer AlxGa1-xN and barrier layer AlyGa1-yN in each cycle are 4nm and 8nm respectively .

The preferred value ranges of the above x and y are 0.1<x<0.4, 0.3<y<0.6.

Correspondingly, the epitaxial wafer structure prepared according to the above method mainly includes the following layers grown sequentially:

Sapphire base;

Low temperature AlN layer;

High temperature AlN layer;

Several periods of ultra-thin AlGaN/AlN layers, the Al composition of AlGaN in each period gradually decreases along the growth direction, and then gradually increases;

A silane-doped n-type AlGaN layer;

Several periods of AlxGa1-xN/AlGaN superlattice layers, x<y;

Several periods of AlxGa1-xN/AlyGa1-yN (y>x) quantum well barrier region, x<y;

doped magnesium p-type AlGaN barrier layer;

doped magnesium p-type AlGaN layer;

doped magnesium p-type GaN layer.

The epitaxial wafer structure is also correspondingly optimized as follows:

In the above-mentioned several periods of ultra-thin AlGaN/AlN layers, each period can first grow 1-3nm in the manner of gradually decreasing Al composition, then grow 1-3nm in the manner of gradually increasing Al composition, and then grow 3nm - 5nm AlN thin layer.

The AlxGa1-xN/AlGaN superlattice layers of the above several periods have a total of 10 periods, and the thickness of each period is 7nm; the AlxGa1-xN/AlyGa1-yN (y>x) quantum well barrier regions of the several periods, There are 8 periods in total, and the thicknesses of the well layer AlxGa1-xN and the barrier layer AlyGa1-yN in each period are 4nm and 8nm respectively.

Above 0.1<x<0.4, 0.3<y<0.6.

The present invention has the following beneficial effects:

The present invention adopts the method of gradually changing the Al composition to dope in the middle of AlN, which can gradually release the stress from the lattice adaptation of the substrate layer, and the gradual composition growth can reduce the defects of the lattice adaptation of the interface, and improve the crystal of the material interface At the same time, the gradual growth can slip dislocations, make threading dislocations segregate, well block threading dislocations from entering the quantum well region, and provide a very good substrate for growing quantum wells, and greatly reduce the The influence of the stress generated by lattice fitting on the growth of quantum wells improves the overall crystallization quality of the material, enhances the spatial overlap of the electron-hole wave function of the quantum well layer, and improves the overall optoelectronic characteristics of the UV LED.

The invention also grows the AlxGa1-xN/AlGaN superlattice layer, which can release the stress, reduce the polarization effect, and further prevent dislocations from entering the quantum well region. The use of AlxGa1-xN/AlyGa1-yN quantum well barrier structure can improve the lattice matching and further improve the luminous recombination efficiency.

Description of drawings

FIG. 1 is an overall structure diagram of the epitaxy of the ultraviolet LED of the present invention.

Fig. 2 is a schematic diagram of the structure of the ultra-thin AlGaN/AlN layer with graded Al composition in the present invention.

detailed description

The present invention uses metal organic compound chemical vapor deposition (MOCVD) epitaxial growth technology, uses sapphire as the growth substrate, and performs heterogeneous epitaxial growth, using trimethylgallium (TMGa), triethylgallium (TEGa), and trimethylindium (TMIn), trimethylaluminum (TMAl) and ammonia (NH3) silane (SiH4) and dimagnesocene (cp2mg) respectively provide gallium source, indium source, aluminum source, and nitrogen source, silicon source, source of magnesium. As shown in Figures 1 and 2, the growth process of the UV LED epitaxy is as follows:

1. After the sapphire substrate is specially cleaned, put it into the MOCVD equipment and bake it at 1100°C for 10 minutes.

2. A low-temperature AlN layer with a thickness of 10 nm is grown at a temperature of 600° C., and the growth pressure is 150 torr.

3. Raise the temperature to 1070°C to grow a high-temperature AlN layer with a thickness of 300nm, and the growth pressure is 150torr.

4. Grow a thin AlGaN layer with graded Al composition at a temperature of 1060°C and 200 torr. The growth process is: at a temperature of 1060°C, turn on TMGa and TMAl, in which TMAl has been kept at 40umol/min, the flow rate of TMGa is gradually increased from 0 to 300umol/min, the growth is 1.5nm, and then the flow rate of TMGa is gradually reduced from 300umol/min to 0, grow 1.5nm; then turn off TMGa, grow 3nm AlN thin layer; repeat 5-10 cycles in this way.

5. Grow a silane-doped n-type AlGaN layer with a thickness of 500nm at a temperature of 1060°C and a pressure of 200torr.

6. At a temperature of 1060°C and 200 torr, grow a layer of AlxGa1-xN/AlGaN superlattice with 10 periods, with a thickness of about 7nm for each period and a total thickness of 70nm.

7. Grow a layer of AlxGa1-xN/AlyGa1-yN (y>x) quantum well barrier layer in a nitrogen atmosphere of 250torr and 1060℃. The thickness of the quantum well layer AlxGa1-xN and the barrier layer AlyGa1-yN are 4nm and 8nm respectively.

8. The temperature is up to 1000°C, 150torr, and a p-type AlGaN layer doped with magnesium is grown with a thickness of 10nm.

9. Grow a 20nm Mg-doped p-type AlGaN layer at 900°C and 200torr.

10. Grow a p-type GaN layer doped with Mg at 850°C and 300 torr.

11. Under nitrogen atmosphere, anneal for 20 minutes.

The epitaxial growth process ends.

Through the test, the test values of the 002 plane and 102 plane of the LED epitaxial wafer XRD (x-ray diffraction) grown by this structure method are respectively reduced by 20% and 15% compared with the test value of the epitaxial wafer of the traditional scheme. The optical power of the traditional epitaxial wafer is increased by 10-15% compared with the chip made under the same process.

It should be emphasized that the specific parameters that can achieve the best technical effect are given in the above examples, but most of these specific parameters such as temperature, thickness, and pressure are conventional choices made with reference to the prior art, and should not be regarded as Restrictions on the protection scope of the claims of the present invention. The technical improvement principle of the present invention is described in the description, and those skilled in the art should be able to realize that the purpose of the present invention can still be basically realized by making appropriate adjustments to each specific parameter under the basic scheme.

Claims (7)

1. a kind of growing method for lifting ultraviolet LED epitaxial material crystalline quality, comprises the following steps：

(1) using sapphire as growth substrate, growing low temperature AlN layers；

(2) grow high-temperature AlN layer；

(3) the ultra-thin AlGaN/AlN layers in several cycles are grown, specifically each cycle is first in the way of Al content gradually variationals reduce Growth 1-3nm, then 1-3nm is grown in the way of Al content gradually variationals increase, then grow the AlN thin layers of 3-5nm；

(4) the N-shaped AlGaN layer of growth of doping silicon alkane；

(5) grow the Al in several cycles_xGa_1-xN/AlGaN superlattice layers；

(6) grow the Al in several cycles_xGa_1-xN/Al_yGa_1-yN SQWs build area, x<y；

(7) grow magnesium-doped p-type AlGaN barrier layer；

(8) grow magnesium-doped p-type AlGaN layer；

(9) grow magnesium-doped p-type GaN layer；

(10) under nitrogen atmosphere, anneal.

2. it is according to claim 1 lifted ultraviolet LED epitaxial material crystalline quality growing method, it is characterised in that step Suddenly in (3), the growth in each cycle is carried out according to following operation：In 1060 DEG C of temperature, TMGa and TMAl, wherein TMAl mono- are opened The straight flow for keeping 40umol/min, TMGa progressively increases to 300umol/min from 0, grows 1.5nm, then is gradually reduced TMGa Flow from 300umol/min to 0, grow 1.5nm；TMGa is then shut off, the AlN thin layers of 3nm are grown.

3. it is according to claim 1 lifted ultraviolet LED epitaxial material crystalline quality growing method, it is characterised in that：Step Suddenly 10 cycles of (5) symbiosis length, the thickness 7nm in each cycle；Step (6) symbiosis 8 cycles of length, the well layer in each cycle Al_xGa_1-xN and barrier layer Al_yGa_1-yThe thickness of N is respectively 4nm and 8nm.

4. according to the arbitrary described growing method for lifting ultraviolet LED epitaxial material crystalline quality of claims 1 to 3, its feature It is：0.1<x<0.4,0.3<y<0.6.

5. a kind of ultraviolet LED epitaxial slice structure, it is characterised in that including the layers below for growing successively：

Sapphire substrates；

Low temperature AI N shell；

High-temperature AlN layer；

The ultra-thin AlGaN/AlN layers in several cycles, each cycle first grow 1-3nm in the way of Al content gradually variationals reduce, then 1-3nm is grown in the way of Al content gradually variationals increase, then grow the AlN thin layers of 3-5nm；

The N-shaped AlGaN layer of doping silane；

The Al in several cycles_xGa_1-xN/AlGaN superlattice layers；

The Al in several cycles_xGa_1-xN/Al_yGa_1-yN SQWs build area, x<y；

Magnesium-doped p-type AlGaN barrier layer；

Magnesium-doped p-type AlGaN layer；

Magnesium-doped p-type GaN layer.

6. ultraviolet LED epitaxial slice structure according to claim 5, it is characterised in that：The Al in several cycles_xGa_{1- x}N/AlGaN superlattice layers, have 10 cycles, the thickness 7nm in each cycle；The Al in several cycles_xGa_1-xN/ Al_yGa_1-yN SQWs build area, have 8 cycles, well layer Al in each cycle_xGa_1-xN and barrier layer Al_yGa_1-yThe thickness of N point Wei not 4nm and 8nm.

7. the ultraviolet LED epitaxial slice structure according to claim 5 or 6, it is characterised in that：0.1<x<0.4,0.3<y<0.6.