CdTe X/γ-ray Detectors with Different Contact Materials

Abstract

Different contact materials and optimization of techniques of their depositions expand the possibilities to obtain high performance room temperature CdTe-based X/γ-ray detectors. The heterostructures with ohmic (MoOx) and Schottky (MoOx, TiOx, TiN, and In) contacts, created by DC reactive magnetron sputtering and vacuum thermal evaporation, as well as In/CdTe/Au diodes with a p-n junction, formed by laser-induced doping, have been developed and investigated. Depending on the surface pre-treatment of semi-insulating p-CdTe crystals, the deposition of a MoOx film formed either ohmic or Schottky contacts. Based on the calculations and I‑V characteristics of the Mo-MoOx/р-CdTe/MoOx-Mo, In/р-CdTe/MoOx-Mo, Ti-TiOx/р-CdTe/MoOx-Mo, and Ti-TiN/р-CdTe/MoOx-Mo Schottky-diode detectors, the current transport processes were described in the models of the carrier generation–recombination within the space-charge region (SCR) at low bias, and space-charge limited current incorporating the Poole–Frenkel effect at higher voltages, respectively. The energies of generation–recombination centers, density of trapping centers, and effective carrier lifetimes were determined. Nanosecond laser irradiation of the In electrode, pre-deposited on the p-CdTe crystals, resulted in extending the voltage range, corresponding to the carrier generation–recombination in the SCR in the I‑V characteristics of the In/CdTe/Au diodes. Such In/CdTe/Au p-n junction diode detectors demonstrated high energy resolutions (7%@59.5 keV, 4%@122 keV, and 1.6%@662 keV).

Characterization of CdTe-based p-n junction-diode x/y-ray detectors formed by frontside laser irradiation

“…The fundamentals of the laser techniques of p-n junction-diode formation were discussed in our earlier works [3][4][5][6] and the mechanism of the laser-induced solid-phase doping of the surface CdTe region by frontside laser irradiation was attributed to the effect of laser-induced shock waves (Figure 1(e)). 5,6,16,17 We used sets of single laser pulses with energy density E both below and above the CdTe melting threshold.…”

“…The fundamentals of the laser techniques of p-n junction-diode formation were discussed in our earlier works [3][4][5][6] and the mechanism of the laser-induced solid-phase doping of the surface CdTe region by frontside laser irradiation was attributed to the effect of laser-induced shock waves (Figure 1(e)). 5,6,16,17 We used sets of single laser pulses with energy density E both below and above the CdTe melting threshold. The In film, which was a donor impurity source during laser action, was not noticeably evaporated even at multiple irradiation and it served as an electrode after doping and formation of a p-n junction under the In/CdTe interface (Figure 1(e-g)).…”

“…The advantages of CdTe-based X/𝛾-ray detectors, designed as diode structures, have encouraged intense development of various fabrication techniques of such kind of sensors. 1,2 We have elaborated diode-type detectors based on either a p-n junction, formed by laser induced doping [3][4][5][6] or Schottky barrier, created using Ar plasma surface processing or different contact materials. [6][7][8] High parameters (energy resolution and detection efficiency) are achieved in both types of diode detectors.…”

“…1,2 We have elaborated diode-type detectors based on either a p-n junction, formed by laser induced doping [3][4][5][6] or Schottky barrier, created using Ar plasma surface processing or different contact materials. [6][7][8] High parameters (energy resolution and detection efficiency) are achieved in both types of diode detectors. CdTe-based p-n junction-diode detectors have attractive features that make promising further study and development of the laser-assisted fabrication techniques of such detectors.…”

“…12,13 Such technique was employed in the present study. Developing the successes, achieved in manufacturing X/𝛾-ray detectors based on CdTe pn junction diodes, formed by the frontside laser irradiation doping technique, [3][4][5][6] we have continued optimizing the technology to obtain sensors with higher functional characteristics. The electrical and spectroscopic characteristics of In/CdTe/Au p-n junction-diode detectors, created by frontside laser irradiation using an additional procedure of lowtemperature annealing of semi-insulating p-like CdTe crystals in vacuum prior to doping with In atoms (donors), contact formation and electrode deposition, have been discussed.…”