Defect Frozen Phenomena in Phosphorus-Doped Hydrogenated Amorphous Silicon

Abstract

Defect frozen phenomenon in hydrogenated amorphous silicon (a-Si: H) was investigated with studying temperature dependence of dc conductivity and excess heat capacity in samples which were cooled at various cooling rates from a thermal equilibrium state kept at 250°C for 1h. Differential scanning calorimetry (DSC) studies of P-doped a-Si: H show the behavior governed by relaxation of defect frozen state which is characterized by the equilibrium temperature T_E. The T_E detected by DSC agrees with the one determined by the temperature dependence of dc conductivity. The temperature dependence of excess heat capacity is successfully interpreted by a simulation based on the model of defect specific heat which is caused by the relaxation process of defect frozen states. The temperature dependence of dc conductivity above T_E is characterized by the activation energy E_a. The experimental relation between T_E and E_a in P-doped and compensated a-Si: H was discussed semi-quantitatively on the basis of a model for frozen defect states. It is suggested that a large amount of D⁰ (neutral dangling bond state) in the compensated sample plays an important role in the relaxation phenomena of defect frozen states.