Photoconductive Measurements On Microwave-Assisted Plasma-Enhanced Chemically Vapor-Deposited Diamond Films

Intrinsic photoconductivity is studied in microwave plasma-enhanced chemically vapor deposited polycrystalline diamond thin films. Two excitation sources are used to excite free carriers: a mode-locked Nd:YAG laser producing UV pulses 3-5 ps in duration of energy 6.2 eV, and a synchrotron source producing 350 ps pulses of broad band X-rays with energy less than 2.5 keV. Both sources are used to study 3-6-mu-m thick polycrystalline diamond films grown by microwave plasma chemical vapor deposition. The procedure used to prepare the films is described. Values for the carrier mobility and lifetime have been extracted from the results. The lifetimes are very short (less than 50 ps), probably because of the high density of defects within the crystallites. The mobility is considerably higher than that reported earlier on diamond films. We extracted a value of approximately 60 cm2 V-1 s-1 at a field of 10(3) V cm-1. The photoresponse of the microwave films as a function of induced carrier density is similar to that of natural diamonds. Specifically, carrier-carrier scattering reduces the mobility at high densities.