Spectroscopy of Nonradiative Recombination Levels by Two‐Wavelength Excited Photoluminescence

The intensity of photoluminescence (PL) changes when an additional below‐gap excitation (BGE) light modifies the electronic occupation of one of the crystalline defects acting as nonradiative recombination (NRR) levels and shifts the balance between radiative and NRR rates. The photon energy of above‐gap excitation (AGE) light selects the layer and determines the depth of inspection, whereas that of BGE corresponds to the energy distribution of the NRR levels. The essential advantage of two‐wavelength excited PL (TWEPL) lies on a systematic combination of BGE spectroscopy and AGE spectroscopy for a variety of materials. It provides the noncontacting and nondestructive detection of NRR levels, distributing in a whole wafer as well as in a microscopic volume. Density and the electron and hole capture rates of NRR level 1, Nt1, Cn1, and Cp1, and those of level 2, Nt2 and Cp2, are determined consistently by the TWEPL measurement with the aid of time‐resolved PL. A brief review is given on the principle of the TWEPL, basic model of analysis, and experimental results of detecting NRR levels in GaAs/AlGaAs, InGaAs/GaAs, InAs/GaAs, GaN, InGaN, AlGaN, and GaPN. The method gives us a guiding compass toward the efficiency improvement of electronic devices from which PL is observable. By observing the photoluminescence (PL) intensity change due to below‐gap excitation (BGE) light, nonradiative recombination (NRR) levels are detected without electrode. The essential advantage lies on the systematic BGE and above‐gap excitation (AGE) spectroscopy, which provides NRR parameters with the aid of time‐resolved PL measurement. The method guides us a way to improve the efficiency and reliability of electronic devices.