Deep level analysis in heterostructure field-effect transistors by means of the photo-FET method

The photo-FET method, a fast and simple room-temperature method for deep level analysis, was applied to heterostructure field-effect transistors for the first time. Well-known donor-like and several unknown acceptor-like levels were detected. By comparing heterostructures and homogeneously doped AlGaAs layers, GaAs- and AlGaAs-related traps could be separated. For comparison, similar samples were investigated independently by photocapacitance- and by low-frequency noise measurements. It was shown experimentally that superlattice buffers reduce the influence of GaAs related traps on the FET current. A simple model is proposed which relates the trap ionization in the AlGaAs to the carrier variation in the TEG.