厚度对GaN薄膜的发光性能的影响

Luminescence Property of GaN Films with Change of Thickness

研究了宝石（γ-Al2O3）衬底上用金属有机物化学气相沉积（MOCVD）系统生长的不同厚度的c面氮化镓（GaN）薄膜的光学性质。研究发现不同厚度GaN薄膜的吸收截止边均在3.38 eV附近，在它们的光致发光（PL）光谱中也观察到了相同位置带边峰。利用透射谱和光致发光光谱中的干涉条纹估算了薄膜的厚度，一致地反映了它们产生的机制相似。正面照射下光致发光光谱中未能观察到明显的黄光带，却观察到了明显的蓝光带，并且随着厚度的增加蓝光带的峰位发生蓝移，发光强度增加，认为这一现象产生的原因是厚度增加的同时杂质能级ON的不断引入和镓空位VGa结合而成VGa-ON复合体越来越多，由于ON成分的增多，VGa-ON复合体所在能级被渐渐拉低。对其中一个样品进行的光致发光反照的测试结果也证明了这一点。

Luminescence properties of GaN films with different thicknesses grown on γ-Al2O3 by MOCVD are studied from the absorption spectra and photoluminescence （PL） spectra. All the absorption spectra of films with different thicknesses have a cut-off edge around 3.38 eV, which is also observed in PL spectra. The thickness is estimated by using the interference fringes in the spectra, and the similar results suggest the same generation mechanism. Yellow luminescence （YL） is not observed in front-side PL excitation, whereas blue luminescence （BL） is obvious, appearing a blue shift in peak position and an increase of light intensity with the increase of the thickness. It is believed that a large number of oxygen impurity are brought in during the epitaxy growth, and the positive ON donor and the negative VGa acceptor can easily form the VGa-ON complex. The energy level of the VGa-ON complex is gradually pulled down with the increasing thickness. The PL spectrum obtained from backside excitation confirms this point.