Terahertz Optoelectronic Properties of Synthetic Single Crystalline Diamond

Abstract

A systematic investigation is performed for the optoelectronic properties of single crystalline diamond (SCD) grown by microwave plasma chemical vapor deposition (MPCVD). It is indicated that, without any intentional doping during the sample growth, the terahertz (THz) optical conduction in SCD is mainly affected by H-terminations, -OH-, O- and N-based functional groups attached to the surface of SCD. By using THz time-domain spectroscopy (TDS), we have measured the transmittance, complex optical conductivity σ(ω) and dielectric constant of SCD. We find that SCD does not show typical semiconductor characteristics in THz regime, where σ(ω) cannot be described rightly by the conventional Drude formula. Via fitting the real part and imaginary parts of σ(ω) with the Drude-Smith formula, the electron density ne , electronic relaxation time τ and electronic backscattering or localization factor have been determined optically. The temperature dependence of these parameters is also measured. From the temperature dependence of ne, a metallic to semiconductor transition is observed at about T=10K. The temperature dependence of τ is mainly induced by electron coupling with acoustic-phonons and there is a significant effect of photon-induced electron backscattering or localization in SCD. This work demonstrates that THz TDS is a powerful technique in studying SCD which contains H- and O-based bonds and has low electron density and high dc resistivity. The interesting and important findings from this study can help us to gain an in-depth understanding of SCD and may provide new guidance for the applications of SCDs as electronic, optical and optoelectronic materials.

Keywords: single crystalline diamond, terahertz time-domain spectroscopy, optoelectronic properties