Multimedia Color Management Photosensor Using Amorphous Photodiode

Abstract

In this paper, a new high optical gain amorphous avalanche photodiode has been successfully fabricated on ITO/glass substrate by plasma enhanced chemical vapor deposition (PECVD). All of these superlattice (SL) structures are made of an a-Si/SiC:H heterojunction to spatially confine the carrier ionization events within the narrow bandgap material (a-Si:H). As the carriers move across the heterobarrier step, they gain kinetic energy from the band edge discontinuity thus effectively reducing the impact ionization threshold energy. In this way each carrier will impact ionize a new electron-hole pair and the ionization rate can be enhanced. The performance of high gain, high sensitivity and low noise can be achieved. Due to the multiplication mechanism in the Si/SiC:H layer, the optical gain will be enhanced. For the a-SiC:H graded-gap superlattice structure, the room-temperature electron and hole impact ionization rates, α and β, have been determined by the photocurrent multiplication measurements. The ratio of the electron to hole ionization rates is 7.743 at a fixed electric field of 2.19×10^5Vcm^(-1). Avalanche multiplication in the superlattice layer yields a high optical gain of 206 at a reverse bias V(subscript R)=20V and an incident light power P(subscript in)=5μW and has a switching time of 7.2μs at a load resistance R(subscript L)=2.2KΩ. Multiplication excess noise is also measured, and is used to evaluate the ionization rate ratio. It was found that the a-SiC:H graded-gap superlattice avalanche photodiode generates high optical gain and low excess noise during the photocurrent multiplication. These results indicate that the a-SiC:H graded-gap superlattice avalanche photodiode is a promising device for the high sensitive imaging sensor. Besides, a variety of peak response wavelength is achievable by changing the applied bias and the well width in the SL structure, making the device useful as a wavelength selective multimedia color management photosensor.