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 TE. The TE 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 TE is characterized by the activation energy Ea. The experimental relation between TE and Ea 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.