A Novel Technique for Deep Level Characterization of High-Resistivity Semiconductor Materials

An improved photo induced current transient spectroscopy (PICTS) technique is developed for studying deep level parameters in high-resistivity semiconductor materials. A new digital data acquisition approach and improvement in the cryogenics of the system have enabled us, for the first time in our laboratory, to detect CuA level in a copper doped silicon compensated gallium arsenide (GaAs:Si:Cu) sample. The digital approach improves both the signal to noise ratio (S/N) and the efficiency of the system. Also, multiple PICTS spectra in a single thermal cycle can be obtained. In the present work, various doped and undoped gallium arsenide ( GaAs) and polycrystalline zinc selenide (ZnSe) crystals are studied. The current transients are analyzed by using two different methods -- a standard rate window method and a curve fitting method. The relative merits and demerits of the two methods are discussed. It has been observed that multiple decay time constants obtained from the curve fitting method consist of sum of the exponentials throughout the temperature range centered around the resonant peak. In particular, this method allows the separation of closely spaced traps within the bandgap.