Because of the lower density of interface states in a-Si:H/a-SiN:H than that in a-Si:H/a-SiC:H, an a-Si:H/a-SiN multilayer reach-through avalanche photodiode is fabricated on an ITO/glass substrate by plasma-enhanced chemical vapor deposition (PECVD) . In order to improve the performance of the a-Si:H/a-SiN:H APD'S, a novel structure is used. By controlling the deposition ratio of silicon and nitrogen of amorphous SiN,the valence band top of a-Si:H is deeper than that of a-SiN:H, that is, the a-Si :H/a-SiN: H system has the electron potential well in a-Si:H, while the hole well is in a-SiN:H, thus we can successfully suppress the hole impact ionization, correspondingly enhance the electron impact ionization effectively.
The measurement of current versus voltage is employed to study the multiplication factors and the impact ionization coefficients. The characteristics of a-Si:H/a-SiN:H APD's,such as I-V curves, optical gains, impact ionization rates, excess noise factors, the relative response and the relationship between the breakdown voltage and wavelength, are studied. The electron multiplication factor is Mc=4.5 at reverse bias V=12v. An optical gain of 3.7 at reverse bias VR=12v and an incident light power Pin=3μw is obtained. Homo junction a-Si:H reach-through APD's and homojunction a-Si:H APD's are also fabricated for comparison.The results show that the novel a-Si:H/a-SiN:H APD's is promising in high-gain, low-noise photodetectors.