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

Abstract

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 (V<0.45V) the diodes with thinner amorphous layers (37 and 86nm) are dominated by recombination in the a-SiGe:H depletion region, whereas the thicker diode (200nm) is dominated by multistep tunneling through depletion region. In addition, at high forward bias (V>0.45V) 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.