AlN成核层厚度对Si上外延GaN的影响

Effect of AlN nucleation layer thickness on the quality of GaN grown on Si(111)

采用低温AlN成核层,在Si(111)衬底上,用金属有机化学气相沉积(MOCVD)法生长了GaN薄膜。采用高分辨X射线衍射(XRD)、椭圆偏振光谱仪和原子力显微镜(AFM)研究了AlN成核层的厚度对GaN外延层的影响。对AlN的测试表明,AlN的表面粗糙度(RMS)随着厚度增加而变大。对GaN的测试表明,所有GaN样品在垂直方向处于压应变状态,并且随AlN厚度增加而略有减弱。GaN的(0002)_ω扫描的峰值半宽(FWHM)随着AlN成核层厚度增加而略有升高,GaN(10-12)_ω扫描的FWHM随着厚度增加而有所下降。(10-12)_ω扫描的FWHM与GaN的刃型穿透位错密度相关,A1N成核层的厚度较大时会降低刃型穿透位错密度,并减弱c轴方向的压应变状态。

GaN thin film with A1N nucleation layer was grown on Si（111） substrates using metal-organic chemical vapor deposition （MOCVD）. High resolution X-ray diffraction （XRD）, ellipsometer and atomic force microscope （AFM） are used to investigate the effect of A1N thickness on GaN film. The results demonstrate that the thickness of low temperature A1N nucleation layer prominently influences the mor- phology of A1N nucleation layers, the crystal quality and stress of GaN epilayers. It is found that the sur- face roughness of A1N samples is larger with thicker A1N nucleation layer. 0--20 scan of （0002） shows that the compressive strain exists on all GaN samples in c-axis direction and reduces slightly with the in- creasing of AIN thickness, co scan shows that FWHM of （0002） increases while FWHM of （10-12） de- creases with the increasing of A1N thickness. FWHM of （10-12） is related with the density of edge-type threading dislocation （ETD）. It means that ETD reduces With the AIN thickness increasing. The change in dislocation density is attributed to the different grain sizes and grain densities on A1N nucleation lay- ers. The crystal quality of GaN epilayer deposited on A1N nucleation layer with large grain size and low grain density is good, since the lateral growth and coalescence of GaN islands are promoted. On the other hand, the A1N nucleation layer with small grain size and high grain density leads to formation of disloca- tions. These dislocations degrade the crystal quality of GaN.