X-ray detection using MOS and PIN diodes biased in the constant reverse current or voltage modes

This article discusses X-ray detection using MOS and PIN diodes biased in the modes of constant reverse current or voltage, aiming at radiological protection and as pixels for direct digital imaging radiography applications. MOS diodes operating with stationary width of the depletion region at a constant reverse current are proposed for X-ray detection using an Al/SiO2(2.20 nm)/Si-P structure fabricated on 10 Ω.cm substrates. A miniature X-ray system (Mini X model from Amptek) was used to illuminate the diodes, at 2 cm away, inside of an aluminum chamber to protect against the X-ray radiation. As a result, the MOS diodes showed good voltage response as function of the bias voltage of the X-ray tube for flux varying from 0 to around 500 mSv/h. In this case, the MOS voltage response increased from 0 to 0.25 mV for the X-ray bias voltage varying from 0 to 40 kV at a filament current of 50 µA. X-ray detection in a constant reverse voltage mode for the MOS diode was unfeasible due to poor current response superimposed to the background electrical noise. On the other hand, unlike the MOS diode, the PIN diode showed good current response in the constant reverse voltage mode as function of the bias voltage of the X-ray tube for flux varying from 0 to around 500 mSv/h. It was noteworthy that the PIN current response increased proportionally with the bias voltage from and 0 to 40 nA at a reverse biasing of -5 V, which are similar to the results reported in the literature for PIN diodes.