Effect of reverse voltage on alpha spectra of pre-conditioned Si PIN diodes deployed in vacuum/ambient environment

Abstract

Semiconductor-based Si PIN diodes are employed for radiation detection owing to their many advantages. However, their performance and reliability heavily rely on their pre-conditioning and the environment in which they are deployed. In this article, the response of Si PIN diodes that are subjected to two different pre-conditions [heat-treated at 100 °C (HT) and exposed to 85% relative humidity (HUM)] and two deployment environments [vacuum and ambient] to alpha particles emanating from triple-alpha source (239Pu-5155 keV, 241Am-5486 keV, and 244Cm-5805 keV) are investigated. Prior to alpha spectroscopy measurements, a meticulous electrical characterization, in terms of reverse current-voltage (IR-VR) and reverse capacitance-voltage (CR-VR) measurements are carried out. The IR-VR characteristics revealed that the leakage current (IR) is higher for measurements performed in ambient as compared to vacuum, while CR-VR characteristics are utilized to set the minimum reverse voltage (VR) that resulted in depletion width commensurate with the range of alpha particles. In order to confirm the optimum VR for maximum charge collection, alpha spectra are obtained in vacuum conditions for different values of VR ranging from 0 to 48.6 V, which showed a left-exponential Gaussian convoluted lineshape. A systematic analysis of the lineshape in terms of the fitting parameters viz, peak position, FWHM, area under the peak, and tailing parameter, revealed that the most robust data is obtained at an optimum VR of 4.6 V, where saturation is observed in peak position, area under the peak and tailing parameter. It is to be added that in the present experiment, 4.6 V is the optimum VR for obtaining robust measurements even for pre-conditioned diodes in different deployment conditions and is thus suitable for field condition measurements.