Influence of the a-SiGe:H thickness on the conduction mechanisms of n-amorphous-SiGe:H∕p-crystalline-Si heterojunction diodes

We have fabricated, electrically characterized and simulated n-type hydrogenated amorphous silicon germanium alloys on p-type crystalline-silicon heterojunction diodes with three different a-SiGe:H layer thicknesses: 37, 86, and 200nm. The capacitance–voltage results confirm the existence of abrupt heterojunctions. The conduction and valence-band discontinuities of the heterojunctions and the electron affinity of the n-type a-SiGe:H films were obtained. The conduction mechanisms were determined by analyzing the temperature dependence of the current–voltage characteristics. The results show that at low forward bias (V0.45V) the space-charge limited effect becomes the main transport mechanism in all the measured devices. The increase in the amorphous layer thickness also causes an increase in the leakage reverse current. Numerical simulations support the proposed transport mechanisms.