Diamond Electronics: Defect Passivation for High Performance Photodetector Operation

Abstract

Deep UV, visible blind, photoconductive devices fabricated on polycrystalline CVD diamond using inter-digitated planar electrodes have shown promising characteristics. The`as-fabricated' device performance is insufficient for many applications; a particularly demanding example is the monitoring of high power excimer lasers operating in the UV, which ideally require visible-blind, radiation hard fast UV detectors. However, post-growth treatments can strongly modify the performance level achieved. In this paper, we show that sequentially applied treatments can progressively change both the gain and speed of these devices. We have used charge sensitive deep level transient spectroscopy (Q-DLTS) to study the effect of these treatments on the defect structure of CVD material. For the first time, we report the realisation of diamond photoconductive devices capable of operating at more than 1 MHz at 193 nm.

Recent developments of diamond detectors for particles and UV radiation

“…Although UV photons have too little energy to displace atoms directly, they interact with atmospheric oxygen to produce ozone and this etches the diamond surface. This effect is not well understood, but is being assessed in connection with the detectors described in section 4.1 [57].…”

“…The carriers from areas with long CCDs dominate the signal, which means that relatively poor-quality diamond can be used provided the electrodes are closely spaced, but the detectors have a highly inhomogeneous spatial response [77]. The high gain can come at the cost of slow response, but by careful tailoring of the material, photoconducting devices operating at >1 MHz have been produced [78,79]. One can also dope the diamond to produce a range of more conventional semiconductor structures, but the relatively deep boron acceptor level and lack of an n-type dopant make this approach difficult.…”

“…The lasers are pulsed at kHz frequencies and the detectors must have a lifetime of a month of continuous operation (∼10 8 pulses), so that the detector can be replaced at the same time as the excimer laser tube. Again, Jackman's group has dominated the field, demonstrating detectors which can follow the 15 ns pulses of the 193 nm excimer lasers as well as the silicon diodes (which have been adopted as standard) and able to withstand more than 10 7 pulses of continuous operation, with tests continuing [57,78,79]. However, at 157 nm, there is no silicon competitor, and the diamond detectors are already being demonstrated as able to match the specifications [83].…”