Deposition and properties of sp2 and sp3 hybridized carbon layer for THz waveguide application

Abstract

In this study we are developing Diamond-Like Carbon (DLC) waveguide/cladding layer for graphene-channel THz injection laser. DLC layer, consisting of sp2 and sp3 hybridized carbon, is deposited by DC Photoemission-Assisted Plasma-Enhanced Chemical Vapor Deposition (PA-PECVD) at different temperatures and achievable thicknesses, with goal to achieve at least 10 μm thickness for THz waveguide, on n-doped or non-doped Si wafer. The influence of deposition temperature on DLC properties has been investigated by means of DC conductivity measurement, AC dielectric constant measurement in MHz region in standard MIS configuration, SIMS measurement, Raman spectroscopy, spectroscopic ellipsometry, FTIR spectroscopy and THz spectroscopy. From the results it is clear, that the DLC structure changes with increase of deposition temperature to act more like conductor and consists of more sp2 bonded carbon atoms instead of sp3. This results in possible thicker dielectric layer deposited at higher temperature in used DC plasma device, but decrease of its ability to be used as a waveguide. However, at about 200 °C we are able to deposit sufficiently thick DLC layers, which should still has suitable properties as a waveguide/cladding in THz region.