Spectroscopy of Non-Radiative Recombination Centers in Semiconductors for Light Emitting Devices

1.概述：通过观察带隙下激发（BGE）光与带隙上激发（AGE）光叠加后带间光致发光（PL）强度的变化，定量研究了体材料和多量子阱（MQW）半导体中的非辐射复合（NRR）中心.将AGE密度降低到单光子计数水平提高了发现NRR中心的灵敏度。通过调节AGE和BGE的能量，可以清楚地观察到多量子阱结构中NRR中心的能量分布及其空间分布. GaAs/AlGaAs多量子阱的研究结果：（1）在未掺杂和Si掺杂的样品中检测到不同的能级，反映了它们的结构和生长条件。(2)通过考虑AGE和BGE的能量依赖性，确定了陷阱的空间和能量分布。(3)与均匀掺杂相反，在调制掺杂阱层中没有NRR中心首次变得清楚。(4)通过考虑AGE和BGE密度依赖性自洽地确定陷阱参数. GaN基半导体中的研究结果：（1）在InGaN/GaN多量子阱中，GaN层中存在NRR中心，BGE能区在1.6 ~ 2.4eV之间。(2)在体相GaN样品中得到了相同的能量分布，表明与MQW的结果一致。(3)探测到GaN/AlGaN多量子阱中的NRR中心，可以用来分析详细的复合动力学。

1. General : By observing the intensity change of band-to-band photoluminescence (PL) due to the superposition of a below-gap excitation (BGE) light on an above-gap excitation (AGE) light, a quantitative study on nonradiative recombination (NRR) centers in bulk and multiple quantum well (MQW) semiconductors became possible. Lowering the AGE density down to the single-photon-counting level improved the sensitivity of finding NRR centers. The energy distribution of the NRR centers and their spatial distribution in MQW structures became clear by tuning the energy of AGE and BGE.2. Results in GaAs/AlGaAs MQW :(1) Various levels were detected in undoped and Si-doped samples, reflecting their structures and growth conditions.(2) Spatial and energy distribution of traps was determined by considering AGE and BGE energy dependence.(3) Contrary to uniform-doping, absence of NRR centers in modulation-doped well layers became clear for the first time.(4) Trap parameters were determined self-consistently by considering the AGE and BGE density dependence.3. Results in GaN-based Semiconductors :(1) In InGaN/GaN MQW, NRR centers were found in GaN layers with the BGE energy region between 1.6 and 2.4 eV.(2) The same energy distribution was obtained in bulk GaN sample, indicating the consistency with the result of MQW.(3) NRR centers in GaN/AlGaN MQW were detected, which can be utilized for analyzing detailed recombination dynamics.