Photoconductive Properties of Polycrystalline Silicon Thin Film Annealed at High Pressure of Deuterium

Abstract

In a polysilicon-based photodetector structure, a polysilicon film is important because it acts as both a light-absorption layer and a conductive path. The grain boundary inside polysilicon acts as an energy barrier to the movement of carriers, and research on its passivation has been attempted. In this study, polysilicon passivation was performed using deuterium bonds (Si-D) instead of conventional hydrogen bonds (Si-H). To investigate the effect of the grain boundary density on passivation, polysilicon with three types of grain sizes was prepared. Annealing was performed at atmospheric and high pressure to increase the diffusion of deuterium into the film. The passivation characteristics of polysilicon were investigated based on the dark current, photocurrent, photo-to-dark current ratio (PDCR), and reliability of the fabricated devices. In the case of devices manufactured at atmospheric pressure, the PDCR was excellent among the devices, but showed low reliability after electrical stress. As the deuterium pressure increased, passivation of the grain boundaries progressed further. The potential height reduction due to the passivation of grain boundaries simultaneously increased the dark current and photocurrent of the device. Therefore, the performance factor, PDCR, did not improve significantly. However, durability evaluation confirmed that the reliability of the device was greatly improved. This means that passivation was maintained at the grain boundaries even during stress. Therefore, when manufacturing polysilicon-based photodetectors, deuterium annealing for the purpose of passivation can have a positive effect on the sensing operation of the device, and the annealing pressure should be selected considering the trade-off relationship between the performance and reliability of the device.

Keywords

• Polysilicon
• photodetector
• deuterium
• grain boundary
• passivation