Properties of n-type tetrahedral amorphous carbon (ta-C)/p-type crystalline silicon heterojunction diodes

Heterojunction diodes fabricated by filtered cathodic vacuum arc (FCVA) deposition of n-type (nitrogen-doped) tetrahedral amorphous carbon (ta-C) on p-type crystalline silicon are analyzed in terms of their electronic and photoresponse properties. The thin ta-C films are deposited at room temperature allowing the ready formation of ideal step junctions. The abrupt nature of the heterojunctions is confirmed from SIMS measurements. Capacitance-voltage (C-V) characteristics also show that with an abrupt heterojunction between ta-C and Si, an interface state density of the order of 10¹¹ cm^-2 is obtained. Dark forward current density-voltage-temperature (J-V-T) characteristics are consistent with a current transport mechanism predominantly controlled by a tunnelling-recombination process through states at the ta-C/Si interface. The photospectral response and photovoltaic behavior of the junction are also presented as a function of doping in the ta-C. The response time of these unoptimized diodes is found to be in the range of 0.1-1.5 μs