Pulsed photo-conductivity and carrier recombination lifetime spectroscopy of metal doped germanium

Abstract

A spectroscopic technique is presented, based on pulsed photo-conductivity and carrier lifetime measurements. The technique is implemented by using excitation light pulses with variable wavelength and duration, to generate excess carriers and to study deep levels as well as their impact on carrier lifetime in semiconductors. The carrier lifetime is measured simultaneously with the photo-ionization response as a function of the excitation photon energy. The technique is based on the analysis of amplitude and decay rate characteristics as a function of the wavelength of the light used for excitation. The photoconductivity transients are probed by microwaves. A calibration technique is discussed to relate the photo-conductivity response to the photo-ionization cross-section and the activation energy of deep levels present in the material. As the technique can be applied at room temperature, measurement conditions can be chosen which are relevant for device operation. The possibilities are illustrated for metal implanted and annealed Ge wafers. The obtained results are compared with those of capacitance-deep level transient spectroscopy analyses on similar samples, and with published results.