Direct Determination of the Barrier Height of Au Contact on p-Type Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films

Abstract

Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) films have a specific film structure, wherein a large number of diamond nanograins are embedded in an a-C:H matrix. The UNCD/a-C:H films possess large optical absorption coefficients of more than 106 cm–1 in the photon energy range between 3 and 6 eV. These optical features are profitable for the application of thin-film based solar cell and UV photodetectors. Although the Metal-Semiconductor-Metal (MSM) geometry is suitable for photodetection by using single-layered UNCD/a-C:H film, the property of film/metal interface hasn’t been investigated in detail. In this study, a direct determination of barrier height of metal contact on p-type UNCD/a-C:H film was performed using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). As a result, it was revealed that the down bending occurs on the film/metal interface, which indicates that depletion layer might appear on the surface of p-type UNCD/a-C:H by this structure. Whereas the surface of UNCD/a-C:H films is oxidized, that band-alignment of that does not change. It is possible that that different physical phenomena from that of single crystalline diamond occurs. There are numerous dangling bonds on the surface of UNCD/a-C:H film, therefore it is supposed that the dangling bonds have greatly affected the surface state.