Spectroscopy of Non-Radiative Recombination Centers in Blue-Light Emitting Semiconductors by Two-Wavelength Excitation Scheme

1.模拟测量系统与激发密度的关系：在单光子计数的基础上，通过引入低噪声锁定放大器，设计了模拟测量系统。测量了由MOCVD生长的GaN的禁带上激发(AGE)密度与禁带下激发(BGE)光引起的发光强度降低之间的关系。实验结果与我们的双态模型吻合较好。分别使用了滤光片D_2灯(4.1 eV)和A：Y激光器(1.17 eV)作为AGE和BGE光源。BGE效应的温度依赖性：在GaN外延层的施主-受主对(DAP)发光的情况下，归一化的光致发光强度定义为有和没有BGE的光致发光强度的比率，I_L；A+B&GT；/I_A，在150K以上为一单位。随着温度降低到150K以下，它急剧下降到0.42，然后在80K以下变得恒定。这归因于电子从两态模型的上层向导带的热发射。通过曲线拟合计算出S的热激活能为0.1eV*，这与我们以前测定的能级一致。黄色发光没有明显的温度依赖性，这对于分析非辐射复合(NRR)过程很重要。GaN基半导体中的带隙以下态：基于这些结果，我们在GaN、InGaN/GaN和GaN/AlGaN多量子阱结构上总结了我们的双波长激发光致发光探测到的NRR中心的空间和能量分布、密度和俘获系数。它们在国际会议上发表，并发表在榜单上的学术期刊上。

1. Analog Measurement System and Excitation Density Dependence :In addition to single-photon-counting, we arranged an analog measurement system by introducing a low-noize lock-in amplifier. The dependence of an above-gap excitation (AGE) density on the PL intensity decrease due to a below-gap excitation (BGE) light was measured for a GaN grown by MOCVD. The result agreed well with our two-states model.A filtered D_2 lamp (4.1 eV) and aNd : YAG laser (1.17 eV) were used as an AGE and BGE light sources.2. Temperature Dependence of the BGE effect:The normalized PL intensity defined as the ratio of PL intensities with and without BGE, I_<A+B>/I_A, was unity above 150 K in case of a donor-acceptor pair (DAP) luminescence of a GaN epitaxial layer. With lowering the temperature below 150K, it decreased steeply down to 0.42 and then became constant below 80K. This is attributed to a thermal emission of electrons from the upper level of the two-states model to the conduction band. A thermal activation energy of 0.1 eV *s calculated by curve fitting, which was consistent with our previous energy determination of the level. No distinct temperature dependence of yellow luminescence is important to analyze nonradiative recombination (NRR) processes.3. Below-Gap States in GaN-based Semiconductors:Based on these results on GaN, InGaN/GaN and GaN/AlGaN multiple quantum well structures, we summarized the spatial and energy distribution, density and capture coefficients of NRR centers detected by our two-wavelength excited PL. They were presented at International Conferences and published in Academic Journals on the list.