PHOTOREFLECTANCE STUDY OF PSEUDOMORPHIC HIGH-ELECTRON-MOBILITY TRANSISTORS

Room temperature photoreflectance (PR) measurements have been carried out on a series of pseudomorphic AlGaAs/InGaAs/AlGaAs high electron mo bility transistor (HEMT) structures with different doping profiles gro wn by molecular beam epitaxy. The GaAs and AlGaAs features in the PR s pectrum were studied and their origins were determined by a sequential etching method. It was found that the GaAs buffer layer and AlGaAs ba rrier layer dominate the GaAs and AlGaAs features in the PR spectrum, respectively. The electric fields for Franz-Keldish oscillations (FKOs ) associated with the E-0 transition of both GaAs and AlGaAs are affec ted by the doping on both sides of the InGaAs channel, but are not dir ectly related to the channel carrier concentration. The aluminum compo sition in the AlxGa1-xAs layers was determined and compared with the r esults of FKO energy and the critical-point energy methods. (C) 1997 A merican Institute of Physics.