PROPERTIES OF N-TYPE TETRAHEDRAL AMORPHOUS-CARBON (TA-C) P-TYPE CRYSTALLINE SILICON HETEROJUNCTION DIODES

Heterojunction diodes fabricated by filtered cathodic vacuum are (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 are confirmed from SLMS 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 10(11) 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 mu s.