Photoconductive properties of lightly N-doped single crystal CVD diamond films

In the preparation of high power diamond photoswitches, thick (more than 100 μm) lightly nitrogen-doped single crystals were grown at LIMHP, for which Differential Interference Contrast Microscopy, Raman spectroscopy, photoluminescence, and cathodoluminescence have confirmed good morphology and very low but well-controlled impurity doping level. In order to evaluate the effect of nitrogen incorporation on the electronic properties of these films, photoconductivity measurements have been carried out. In an initial study, I–V and transient photocurrent measurements were conducted on several films with N-doping from 0 to 20 ppm intentionally added to the gas phase during growth, resulting into nitrogen concentrations lower than 100 ppb in the film. The results of these measurements are presented showing typical semiconductor behavior in terms of gain versus settling time, relatively high external quantum efficiency (EQE) and corresponding derived μτ (mobility × lifetime) product. In particular, samples with no nitrogen showed EQEs of several hundreds while their settling time was quite long (tens of seconds). However, samples with small nitrogen addition were observed to have settling times decreasing below a few seconds while EQEs close to 10 showed that a compromise could be found between efficiency and response time.