Thermally induced metastability in compensated and delta-doped amorphous silicon

Abstract

We have studied the conductivity changes induced by thermal quenching in compensated hydrogenated amorphous silicon (a-Si: H) films with various compensation ratios of boron and phosphorus as well as in delta-doped a-Si: H films. The magnitude of the excess conductivity upon rapid cooling increases as the Fermi level approaches the band edges. We suggest a microscopic mechanism for generation of excess carriers by rapid cooling through dopant activation. The relaxation of the excess conductivity follows a stretched-exponential form. However, the activation energy for the relaxation time is found to be smaller than those for both undoped and singly doped a-Si: H films.