Spectra broadening of point-contact Andreev reflection measurement on GaMnAs

Abstract

Point-contact Andreev reflection measurements on Ga0.94Mn0.06As were investigated using Pb tips. The observed conductance versus voltage spectra exhibited behaviors which were described by the modified Blonder–Tinkham–Klapwijk model but with significant broadening. We propose a model by introducing a spreading resistance and compare with an existing model which included effective temperature as a parameter. In as-grown/annealed Ga0.94Mn0.06As samples, we extracted conduction electron spin polarization of 76%/74% from our model, instead of 90%/82% from the one with the effective temperature.