Optical characterization of diamond MIS capacitors

The transient photoresponse properties of diamond metal-insulator-semiconductor (MIS) capacitors have been characterized for the first time. Capacitors were fabricated on natural diamond using an electrochemical cleaning step with a CVD SiO₂ dielectric and an optional carbon implantation to create a nonuniform doping profile. Devices were found to function as integrating photodetectors and were evaluated by the spectral dependence of the transient photocapacitance (PC). We discuss a model that distinguishes between the responses due to inversion layer population and that due to bulk trap occupancy changes. Inversion charge generation was observed at all wavelengths investigated and it dominated the PC transient at photon energies above 3 eV. Possible reasons for this result are discussed and analyzed. We could not demonstrate a suitable way to use carbon implantation to form a surface n-type layer in a MIS device without degrading the device IV properties and eliminating the integrating photoresponse observed on non-implanted devices. These results suggest that diamond charge-storage devices can function only if the diamond surface is prepared properly before device fabrication