In/CdTe/Au p–n junction-diode X/[formula omitted]-ray detectors formed by frontside laser irradiation doping

Abstract

The fabricated In/p-CdTe/Au diode structures with Schottky (In/p-CdTe) and quasi-ohmic (Au/p-CdTe) contacts were transformed into p–n junction diodes by applying the developed frontside laser irradiation doping technique. The Schottky diodes with In and Au electrodes (both with thickness of 400 nm), deposited on the chemically pre-treated B- and A-face of the detector-grade CdTe(111) single crystals, respectively, were subjected to multiple (from tens to thousands times) irradiation from the In film side with series of nanosecond pulses of a KrF excimer laser. As a result of such irradiation, a thin heavily doped n-type CdTe:In layer was formed, a shallow abrupt p–n junction was created and thus the In/CdTe/Au Schottky diode was transformed into the In/CdTe/Au p–n junction diode. The temperature distributions in the In/CdTe/Au structure under laser irradiation were calculated and the I–V characteristics of the diodes were measured for different energy densities E and number N of laser pulses, respectively. The processes of frontside laser irradiation doping and carrier charge transport mechanisms in the created In/CdTe/Au p–n junction diodes were discussed. The samples with higher performance were obtained when only a part of the In electrode thickness was melted during a single laser action (E∼110 mJ/cm 2) and repeated (N∼300–500) irradiation was employed. The fabricated In/CdTe/Au p–n junction-diode structures with relative low reverse dark currents (∼20–50 nA/cm2) were quite sensitive to X/γ-rays and demonstrated sufficient ability to detect the emission of 241Am, 57Co, and 137Cs isotopes. It has been shown that applying the frontside laser irradiation doping technique to In/CdTe/Au structures, it is possible to transform Schottky diodes with low characteristics into highly rectifying In/CdTe/Au p–n junction diodes which are X/γ-ray detectors with moderate or even high detection parameters.