H_2载气流量对AlN缓冲层生长的影响

Influence of H_2 Carrier Gas on Epitaxy of AlN Buffer Layer

在Si(111)衬底上用金属有机化学气相沉积(MOCVD)设备生长了AlN和GaN薄膜。采用高分辨X射线衍射、椭圆偏振光谱仪和原子力显微镜研究了AlN缓冲层生长时的载气(H2)流量变化对GaN外延层的影响。椭圆偏振仪测试表明:相同生长时间内AlN的厚度随着H2流量的增加而增加,即H2流量增加会导致AlN生长速率的提高。原子力显微镜测试表明:随着H2流量的增加,AlN表面粗糙度也呈上升趋势。XRD测试表明:随着AlN生长时的H2流量的增加,GaN的(0002)和(1012)峰值半宽增大,即螺型穿透位错密度和刃型穿透位错密度增加。可能是由于AlN缓冲层的表面形貌较差,导致GaN的晶体质量有所下降。实验结果表明:采用较低的H2流量生长AlN缓冲层可以控制AlN的生长速率,在一定程度上有助于提高GaN的晶体质量。

A1N buffer and GaN epitaxial layer were prepared by MOCVD on Si （ 111 ） substrate. The effect of H2 carrier gas flow for A1N buffer epitaxy on GaN was investigated by high resolution X-ray diffraction, ellipsometer and atomic force microscope. It is found that A1N thickness increases （i. e. the increasing of A1N growth rate） with the increasing of H2 flow. The surface roughness of AIN also tends to increase. The change in surface roughness is attributed to the enhancement of island-growth mode. The increasing of A1N buffer thickness contributes to the increasing of tensile stress which promotes A1N island growth mode. The higher density of islands with bad orientation was observed by AFM on A1N buffer layer which was grown with higher H2 flow. to scan of （0002） and （101-2） show that the increasing of H2 flow leads to the increasing in FWHM of GaN （i. e. the increasing in density of screw threading dislocation and edge threading dislocation）. Because the three-dimension- al growth of GaN starts on the top of A1N islands, the AIN buffer layer with high density of islandscontributes to rapid coalescence of GaN islands that will lead high density of edge threading disloca- tion. The bad orientation of A1N islands on buffer layer will lead to GaN thin film with high density of screw threading dislocation. The obtained data demonstrate that the H2 carrier gas flow plays an important role in improving the crystal quality of GaN.