CN100557772C - Growth method of gallium polar gallium nitride buffer layer - Google Patents

Abstract

The invention relates to a growth method of a gallium polar gallium nitride buffer layer, relating to a gallium nitride buffer layer, in particular to a method for growing a gallium nitride buffer layer by adopting four steps. A growth method of a pure gallium polar gallium nitride buffer layer with less dislocation is provided. The first gallium nitride buffer layer is grown on a sapphire substrate at a high temperature of 1030-1050°C; the high temperature is maintained for a period of time in a pure _H2 atmosphere to make the nitrogen polarity in the first gallium nitride buffer layer Gallium nitride is completely sublimated; the temperature is lowered, and the second layer of gallium nitride buffer layer is grown at low temperature on the remaining gallium polar gallium nitride and sapphire substrate; high-temperature annealing in pure H ₂ atmosphere, pure gallium polar nitrogen GaN buffer layer.

Description

Growth method of gallium polar gallium nitride buffer layer

technical field

The invention relates to a gallium nitride buffer layer, in particular to a method for growing a gallium nitride (GaN) buffer layer in four steps.

Background technique

In recent years, metal-organic chemical vapor deposition (MOCVD) technology has been widely used in the preparation of GaN materials. Due to the simple equipment, high growth rate and easy doping control of this material growth method, it is currently a main method for preparing GaN epitaxial layers. People have successfully prepared GaN films with better quality by using this method. At present, the MOCVD epitaxial GaN film mainly uses α-Al ₂ O ₃ substrate, which has a large lattice mismatch and thermal mismatch with the GaN material, so there is a large stress and high dislocation in the epitaxial GaN material density. In order to reduce the interface free energy between GaN and the substrate, a thin low-temperature buffer layer is first deposited on the substrate. The physical properties of the low-temperature buffer layer are between the substrate and GaN, which can effectively reduce the interface free energy. able. Using a low-temperature buffer layer, people have obtained high-quality GaN single crystals by heteroepitaxy, which reduces the dislocation density by 3 to 4 orders of magnitude (H. Amano, N. Sawaki, I. Akasaki and T. Toyoda: Appl. Phys. Lett. 1986, 48:353). Referring to Fig. 1, the wurtzite GaN buffer layer (Bufferlayer) 2 and high-temperature epitaxial GaN film (Epi-layer) 5 grown on the substrate (α-Al ₂ O ₃ ) 1 usually have gallium polarity (Ga-) 4 and nitrogen polarity (N-) 3, in Figure 1, A represents the growth sequence, and the crystal axis directions are [0001] and [0001], respectively. The structure and electrical properties of GaN grown on the two polar planes are different: gallium polar GaN epitaxial layer is easy to achieve a bright and flat crystal surface, while the nitrogen polar GaN surface is covered with rough surfaces with hexagonal pyramid structures ; Compared with nitrogen polar GaN, gallium polar GaN has better electron mobility and low background (n-type) doping concentration; when making metal-p-type GaN ohmic contact at the same time, the contact resistance of gallium polar GaN Two orders of magnitude less polar than nitrogen (M. Sumiya and S. Fuke: MRS Internet J. Nitride Semicond. 2004, 9: 1). Therefore, in order to produce high-quality GaN-based semiconductor devices, it is very important to control the acquisition of gallium-polar GaN during the epitaxial growth process.

The traditional method (see Figure 2) grows GaN on the low-temperature buffer layer 2. GaN nucleation initially forms columns with [0001] axes. The axis directions of these columns are arbitrary and not all aligned with the sapphire substrate 1. The direction of [0001] is the same, and these pillars are interlaced to form a faulted zone (Faulted zone) 9 . But those pillars whose axes coincide with the [0001] direction of the substrate grow the fastest, so finally the pillars whose axes are all perpendicular to the substrate are left. These pillars then begin to grow in islands and cover smaller islands to form a semi-sound zone10. Finally, it grows horizontally, and the islands are aggregated together to form a sound zone (Sound zone) 11 . Finally, a flat GaN crystal 12 (K.Hiramatsu, S.Itoh, H.Amano, I.Akasaki, N.Kuwano, T.Shiraishi, K.Oki, J.Crystal Growth.1991, 115 :628). It can be seen that the GaN grown on the low-temperature buffer layer by the traditional method has mixed polarity in the initial stage, and the direction is random, forming defect regions, semi-acoustic regions and acoustic regions with poor crystal quality. In Fig. 2, code 13 denotes a dislocation.

GaN is grown directly on the sapphire substrate 1 (see Figure 3) at high temperature. Although it is impossible to obtain GaN crystals with large area, uniform polarity and high quality, the direction of GaN is relatively single in the early stage of growth. These GaN are all hexagonal prism structures. , and the axis directions are [0001] and [0001], both perpendicular to the α-plane of sapphire, showing gallium polarity 4 and nitrogen polarity 3, respectively. (I. Akasaki, H. Amano, Y. Koide, K. Hiramatsu, N. Sawaki, J. Crystal Growth. 1989, 98: 209). However, the thermal stability of nitrogen-polar GaN is lower than that of gallium-polar GaN. Nitrogen-polar GaN sublimates at about 900-950°C, while gallium-polar GaN is still relatively stable above 1000°C (M.Sumiya, N. Ogusu, Y. Yotsuda, M. Itoh, S. Fuke, T. Nakamura, S. Mochizuki, T. Sano, S. Kamiyama, H. Amano, I. Akasaki, J. Appl. Phys. 2003, 93: 1311) .

Contents of the invention

The purpose of the present invention is to provide a simple gallium polar nitrogen with less dislocations for the problems of poor quality defect regions, semi-acoustic regions, and acoustic regions in the epitaxial layer grown in the existing low-temperature buffer layer growth method. Growth method of GaN buffer layer.

The technical solution of the present invention is to utilize the lower thermal stability of nitrogen-polar GaN than gallium-polar GaN, nitrogen-polar GaN sublimates at 900-950°C, while gallium-polar GaN is still relatively stable at temperatures above 1000°C, First grow GaN directly on the sapphire at high temperature, then completely sublimate the nitrogen polar GaN, and retain the gallium polar GaN that maintains good crystal quality, then grow a low-temperature buffer layer, high-temperature annealing, and finally high-temperature epitaxy GaN on this buffer layer Thin film, so as to realize the growth of high-quality GaN epitaxial layer.

The present invention comprises the following steps:

1) The first gallium nitride buffer layer is grown on a sapphire (α-Al ₂ O ₃ ) substrate at high temperature, and the temperature for high temperature growth is 1030-1050°C;

2) Keep the high temperature for a period of time in the pure _H2 atmosphere, so that the nitrogen-polar gallium nitride in the first layer of gallium nitride buffer layer is completely sublimated;

3) lower the temperature, and grow a second gallium nitride buffer layer at low temperature on the remaining gallium polar gallium nitride and sapphire substrate;

4) High-temperature annealing in a pure H ₂ atmosphere to obtain a pure gallium polar gallium nitride buffer layer.

The thickness of the first GaN buffer layer is preferably 20-50 nm.

The temperature for maintaining high temperature for a period of time in pure H ₂ atmosphere is preferably 900-950°C, and the time for maintaining high temperature is preferably 5-10 minutes.

The temperature for growing the second gallium nitride buffer layer at low temperature is preferably 500-600° C., and the thickness of the second gallium nitride buffer layer is preferably 20-30 nm.

The temperature of the high-temperature annealing in the pure H ₂ atmosphere is preferably 980-1000° C., and the annealing time is preferably 5-10 minutes.

Compared with the existing low-temperature buffer layer growth method, the present invention has the following outstanding advantages:

1) The gallium nitride buffer layer is grown on a sapphire (α-Al ₂ O ₃ ) substrate at high temperature, and its growth direction is relatively single. There are only two polarities of gallium and nitrogen, and the crystal axis directions are [0001] and [0001] and [0001] respectively. 0001], and are perpendicular to the substrate plane.

2) The thermal stability of gallium polar gallium nitride and nitrogen polar gallium nitride is quite different, using this characteristic to effectively eliminate the nitrogen polar gallium nitride that leads to the deterioration of crystal quality, and obtain a single gallium polar nitride gallium.

3) Since the second gallium nitride buffer layer is continuously grown at low temperature on the gallium polar gallium nitride remaining after the first high-temperature sublimation and annealed, island-shaped GaN with a single gallium polarity is obtained.

4) Since the island-shaped GaN with a single gallium polarity is obtained, it is beneficial to continue growing on the island-shaped GaN with a single gallium polarity to obtain a high-quality single-gallium polar epitaxial layer.

Description of drawings

Fig. 1 is a schematic diagram of growing a GaN buffer layer and an epitaxial GaN thin film on a sapphire substrate by a traditional method.

Figure 2 shows the GaN low-temperature buffer layer grown on the sapphire substrate by the traditional method, and the epitaxial GaN thin film on the buffer layer.

Fig. 3 shows gallium-polar GaN and nitrogen-polar GaN obtained by directly growing GaN on a sapphire substrate at a high temperature using an existing method.

FIG. 4 shows the specific process of growing a GaN buffer layer on a sapphire substrate and the epitaxial GaN thin film on the buffer layer according to the embodiment of the present invention.

Detailed ways

The substantive characteristics and remarkable progress of the present invention will be further clarified through the elaboration of specific embodiments below.

Example 1

Referring to Figure 4, the growth of GaN uses α-Al ₂ O ₃ as the substrate 1, and first treats it with H ₂ at 1080°C for 10 minutes to completely remove the surface damage layer (process a); then lowers the temperature to 1050°C to grow the first layer GaN buffer layer, the growth time is 180s, and the thickness is about 30mm (process b). At this time, the grown GaN is a hexagonal prism, which are gallium polar gallium nitride 4 and nitrogen polar gallium nitride 3 respectively; then turn off the GaN source and N source, lower the temperature to 950°C in H ₂ atmosphere, and keep this temperature for 300s (process c), the nitrogen polar GaN 3 will be completely sublimated, and only the gallium polar GaN 4 will remain; then Lower the temperature to 530°C, grow the second gallium nitride buffer layer (both crystalline and amorphous states) 5 (process d), the growth time is 120s, and the thickness is about 20nm; turn off the Ga source and N source, in H _2. Under the atmosphere, raise the temperature to 1000°C for annealing (process e), the annealing time is 300s, and the second gallium nitride buffer layer 5 will be polymerized on the remaining gallium polar gallium nitride 4 to form an island-like nitride Gallium 6, and these islands exhibit uniform gallium polarity; finally, the temperature is raised to 1050° C. to continue growth (process f), GaN grows laterally along the above-mentioned islands, and finally a flat GaN film 7 grows.

Example 2

Referring to Figure 4, the growth of GaN uses α-Al ₂ O ₃ as the substrate 1, and first treats it with H ₂ at 1080°C for 10 minutes to completely remove the surface damage layer (process a); then lowers the temperature to 1050°C to grow the first layer The gallium nitride buffer layer, the growth time is 300s, the thickness is about 50nm (process b), the GaN grown at this time is a hexagonal prism, respectively gallium polar gallium nitride 4 and nitrogen polar gallium nitride 3; then turn off the GaN source and N source, lower the temperature to 900°C in H ₂ atmosphere, and keep this temperature for 600s (process c), the nitrogen polar GaN 3 will be completely sublimated, and only the gallium polar GaN 4 will remain; then Lower the temperature to 600°C, grow the second gallium nitride buffer layer (both crystalline and amorphous states) 5 (process d), the growth time is 180s, and the thickness is about 30nm; turn off the Ga source and N source, in H _2. Under the atmosphere, raise the temperature to 980°C for annealing (process e), the annealing time is 600s, the second gallium nitride buffer layer 5 will be polymerized on the remaining gallium polar gallium nitride 4 to form an island-shaped nitride Gallium 6, and these islands exhibit uniform gallium polarity; finally, the temperature is raised to 1050° C. to continue growth (process f), GaN grows laterally along the above-mentioned islands, and finally a flat GaN film 7 grows.

Example 3

Referring to Figure 4, the growth of GaN uses α-Al ₂ O ₃ as the substrate 1, and first treats it with H ₂ at 1080°C for 10 minutes to completely remove the surface damage layer (process a); then lowers the temperature to 1050°C to grow the first layer GaN buffer layer, the growth time is 240s, and the thickness is about 40mm (process b). At this time, the grown GaN is a hexagonal prism, which are gallium polar gallium nitride 4 and nitrogen polar gallium nitride 3; then turn off the GaN Source and N source, lower the temperature to 930°C in H ₂ atmosphere, and keep this temperature for 400s (process c), the nitrogen polar GaN 3 will be completely sublimated, and only the gallium polar GaN 4 will remain; then Lower the temperature to 500°C, grow the second gallium nitride buffer layer (both crystalline and amorphous states) 5 (process d), the growth time is 150s, and the thickness is about 25nm; turn off the Ga source and N source, in H _2. Under the atmosphere, raise the temperature to 990°C for annealing (process e), the annealing time is 450s, the second gallium nitride buffer layer 5 will be polymerized on the remaining gallium polar gallium nitride 4 to form an island-like nitride Gallium 6, and these islands exhibit uniform gallium polarity; finally, the temperature is raised to 1050° C. to continue growth (process f), GaN grows laterally along the above-mentioned islands, and finally a flat GaN film 7 grows.

Claims (4)

1. the growing method of gallium-polar gallium nitride buffer layer is characterized in that may further comprise the steps:

1) high growth temperature ground floor gallium nitride resilient coating on Sapphire Substrate, the temperature of high growth temperature is 1030～1050 ℃;

2) at pure H ₂Keeping temperature in the atmosphere is 900～950 ℃, and the time of maintenance is 5～10min, makes that nitrogen polarity gallium nitride distils fully in the ground floor gallium nitride resilient coating;

3) reduce temperature, growth second layer gallium nitride resilient coating on gallium-polar gallium nitride that remains and Sapphire Substrate, the temperature of growth second layer gallium nitride resilient coating is 500～600 ℃;

4) at pure H ₂Atmosphere annealing gets simple gallium-polar gallium nitride buffer layer, and the temperature of annealing is 980～1000 ℃.

2. the growing method of gallium-polar gallium nitride buffer layer as claimed in claim 1, the thickness that it is characterized in that ground floor gallium nitride resilient coating is 20～50nm.

3. the growing method of gallium-polar gallium nitride buffer layer as claimed in claim 1, the thickness that it is characterized in that second layer gallium nitride resilient coating is 20～30nm.

4. the growing method of gallium-polar gallium nitride buffer layer as claimed in claim 1, the time that it is characterized in that described annealing is 5～10min.

Images