HETEROJUNCTIONS OF SOLID C-60 AND CRYSTALLINE SILICON - RECTIFYING PROPERTIES AND ENERGY-BAND MODELS

Heterojunctions of undoped solid C-60 and n- or p-type-doped crystalline Si have been obtained. Current-voltage measurements show that both C-60/n-Si and C-60/p-Si contacts are rectifying but their directions of rectification are opposite. Thermal activation measurements at a fixed foward bias show an exponential dependence of current on the reciprocal of temperature, from which we determine the effective barrier height as 0.30 eV for C-60/n-Si and 0.48 eV for C-60/p-Si. Using energy-band models for heterojunctions we assign values to the positions of the conduction and valence bands of the solid C-60 relative to those of crystalline Si and derive the electron affinity and band gap of solid C-60 film as 3.92 eV and <1.72 eV, respectively.