Electrical Interface Characterization of Ultrathin Amorphous Silicon Layers on Crystalline Silicon

Heterojunctions of amorphous (a-Si) and crystalline (c-Si) silicon combine the favorable absorption characteristics of a-Si for the solar spectrum, high energy conversion efficiencies, low processing temperatures, potential for low production costs, and a reduced amount of silicon used due to thin a-Si films. To investigate a-Si/c-Si heterojunctions, amorphous p-type silicon (a-Si) with a thickness of 5 nm is deposited via radio frequency-pulsed magnetron sputtering on p-doped, (100)-oriented, crystalline silicon (c-Si) wafers. During deposition, the crystalline silicon wafers are kept at 430 degrees C and the hydrogen flow rate is varied from 0 to 50 sccm (standard cubic centimeters per minute). Temperature-dependent current-voltage measurements are carried out to investigate the dominant transport mechanisms of electrical conduction. Moreover, the influence of hydrogen on physical properties such as barrier height, activation energy, and electrical conductivity is analyzed. A current-voltage dependence as predicted by the thermionic emission model for the low forward-bias region below 0.25 V is observed. Temperature regimes for nearest neighbor hopping and band conduction are revealed by the Arrhenius plot and are found to depend on the hydrogen flow rate.