Nuclear Inst. and Methods in Physics Research, A 1029 (2022) 166397 Contents lists available at ScienceDirect Nuclear Inst. and Methods in Physics Research, A journal homepage: www.elsevier.com/locate/nima In/CdTe/Au p–n junction-diode X/ -ray detectors formed by frontside laser irradiation doping Volodymyr Gnatyuk V.E. Lashkaryov Institute of Semiconductor Physics of the National Academy of Sciences of Ukraine, Prospekt Nauky 41, Kyiv 03028, Ukraine ARTICLE INFO Keywords: CdTe crystal Frontside laser irradiation doping Schottky diode p–n junction diode I-V characteristics X/ -ray detector Isotope emission spectra 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/cm 2 ) were quite sensitive to X/ -rays and demonstrated sufficient ability to detect the emission of 241 Am, 57 Co, and 137 Cs 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/ -ray detectors with moderate or even high detection parameters. 1. Introduction High-resistivity CdTe semiconductor is known as one of the most widely and successfully employed material for room-temperature X/ - ray detectors with high energy resolution [1–4]. In order to effectively collect photogenerated charge carriers, and thus to ensure high de- tection efficiency and energy resolution of radiation sensors, a strong electrical field needs to be applied to a semiconductor crystal how- ever, this way is limited because of increasing dark (leakage) current which severely affects the detector performance [1–4]. A great effort to overcome this problem has been made by developing CdTe-based detectors as diode structures using blocking electrical contacts (Schot- tky barrier) [1–4] or electrical junctions (p-n or p-i-n structure) [4–7] that increases effective resistance of detectors far above the bulk semi- conductor resistance. Indeed, diode-type detectors, either Schottky or p-n diodes, operating at reverse bias, show much lower dark currents comparing with ohmic detectors that allows us to apply increased bias voltage (up to 1 kV and higher) and thereby expand the depletion region in the diode and enhance the collection of photogenerated charge carriers. As a result, an extremely high energy resolution and E-mail address: gnatyuk@ua.fm. quite attractive other characteristics (detection efficiency, radiation resistance, time stability, etc.) in diode-type X/ -ray detectors are achieved [2–6]. Possibilities to use CdTe diodes with a p–n junction as X/ -ray detectors were shown much earlier [7] than application of CdTe diodes with a Schottky contact for such purpose [1–4]. However, even though CdTe-based p–n or p-i-n structured detectors could exhibit a quite high energy resolution, for efficient operation they required lower temper- atures (T =−30–40 ◦ C) [5,6]. Therefore, it is Schottky diodes that are most intensively studied and widely used as high-energy resolution X/ -ray detectors in many application areas [1–4]. This is due to the problem of creation of a built-in shallow quite abrupt p–n junction since efficient n-type doping of high-resistivity CdTe semiconductor has still remained a critical challenge [1,8]. In this regard, the laser-assisted methods of doping of semiconductors seem to be very attractive and promising [9]. The formation of Schottky contacts using different electrode metals are much better studied and different techniques of creation of CdTe Schottky-diode detectors are well developed [1–4,10–14]. However, https://doi.org/10.1016/j.nima.2022.166397 Received 16 January 2022; Received in revised form 17 January 2022; Accepted 2 February 2022 Available online 9 February 2022 0168-9002/© 2022 Elsevier B.V. All rights reserved.