A simple method for detection and quantitative estimation of deep levels in a barrier layer of AlGaN/GaN HEMT structures by analysis of light induced threshold voltage shift

The characterization of deep levels in AlGaN/gallium nitride (GaN) heterostructures is one of the most important problems in GaN high electron mobility transistor (HEMT) technology. This work reports on a technique for determination of deep level concentration in AlGaN/GaN HEMT structures. The proposed method is relatively simple, and it is based on the detection of free holes created by optically induced transitions of electrons from the deep levels to the conduction band. The developed method can detect and provide quantitative estimation of deep level traps in a barrier layer of AlGaN/GaN HEMT structures. Furthermore, it provides a framework for analysis of light induced threshold voltage shift, which includes an important experimental criterion of determination whether the holes are generated or not in the AlGaN/GaN HEMT structures by subbandgap illumination. The method was verified by applying it to a study of the deep levels in GaN HEMTs grown on various substrates, i.e., SiC and GaN.