调制掺杂Al_xGa_(1-x)N/GaN异质结构的微应变

Microstrain in modulation-doped Al_xGa_(1-x) N/GaN heterostructures

用MOCVD方法在 (0 0 0 1)取向的蓝宝石 (α -Al2 O3)衬底上生长了不同势垒层厚度的Al0 .2 2Ga0 .78N/GaN异质结构 ,利用高分辨X射线衍射 (HRXRD)测量了其对称反射 (0 0 0 2 )和非对称反射 (10 14 )的倒易空间图 (RSM )。分析结果表明 ,势垒层内部微结构与应变状态和下层i -GaN的微结构与应变状态互相关联 ,当厚度大于 75 0 时 ,势垒层开始发生应变弛豫 ,临界厚度大于5 0 0 。势垒层具有一种“非常规”应变弛豫状态 ,这种状态的来源可能与n -AlGaN的内部缺陷以及i-GaN/α -Al2

Modulation-doped Al x Ga 1- x N/GaN heterostructures with various thickness of Si-doped n-Al 0.22 Ga 0.78 N barrier (n-AlGaN) were deposited on (0001)-oriented sapphire (α-Al 2O 3) by MOCVD. The reciprocal space mappings (RSMs) of symmetric reflection (0002) and asymmetric reflection (1014) were measured with the methods of high resolution X-ray diffraction (HRXRD). The results indicate that the microstructure and strain status of barrier correlate to those of the i-GaN layer. The strained barrier starts to be relaxed while its thickness is larger than 750 and the critical thickness t c is larger than 500. The barrier holds an 'abnormal' relaxation status, which probably results from the internal defects of n-AlGaN and the strain relaxation status at the i-GaN/α-Al 2O 3 interfaces.