High reverse breakdown a-C:H/Si diodes manufactured by rf-PECVD

Thin films of hydrogenated amorphous carbon ( a-C:H) deposited by radio frequency plasma-enhanced chemical vapour deposition ( rf-PECVD) have been studied for various applications. An interesting property of these films is their high breakdown strength ( 10(7) Vcm(-1)). This property of a-C:H can be exploited in high breakdown heterostructure diodes or as passivation layers and insulator layers in MIS devices. Reports on the applications of a-C:H/Si diodes exist in the literature. Diodes in which the a-C:H films have been deposited by rf-PECVD, have been reported only once. In this article the diodes produced reportedly failed to exhibit reproducible I-V characteristics under high voltage stress. We have investigated the process dependence of structural and electrical properties of rf-PECVD a-C:H films deposited at room temperature front a CH4/Ar gas mixture (at a pressure of 100 mTorr) using a capacitively coupled rf-PECVD. WI: observe a clear correlation between the de-self bias and the rectification ratio of a-C:H/Si heterojunction diodes. Optimised diodes show rectification ratios upto 10(4) and a stable reverse breakdown voltage, typically around 850 V. I-V and C-V measurements show no evidence of hystersis. Scanning Electron Microscopy was carried out to determine the quality of the films deposited. Micro-Raman analysis was used to estimate the I-D/I-G ratio in the films deposited under different dc-self bias.