Temperature dependence of photoluminescence properties of In-doped cadmium zinc telluride
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Temperature-dependent photoluminescence (PL) spectra were measured to characterize the In-doped cadmium zinc telluride (CdZnTe, or CZT) crystals along the growth direction in the range of 10 to 60 K. High-resistivity CZT samples with 1.2 ppm In dopant at the tip and low-resistivity samples with 60 ppm In dopant at the heel have been assessed. The PL intensity quenching of D0X were fitted with two activation energies for high-resistivity CZT sample and only one activation energy for low-resistivity sample, respectively, suggesting different recombination mechanisms. The C-line was observed in the PL spectra of low-resistivity CZT sample and considered to the results of the isoelectronic complexes, InCd–VCd–InCd, while in high-resistivity CZT sample, shallow donor accepted pair (DAP) transition was identified, and thought to be related to InCd–VCd. The A-center in PL spectra was observed in low-resistivity CZT sample, which is indicative of more cadmium vacancies. It turns out that indium in low-resistivity CZT sample has not been doped as efficiently as in high-resistivity CZT sample because of the self-compensation.
I. INTRODUCTION
Cadmium zinc telluride (Cd1−xZnxTe or CZT) has been considered to be the preferred material for the manufacture of room-temperature nuclear radiation detectors.1–3 Indium is often introduced as donors to compensate the cadmium vacancies. However, both low- or medium-resistivity n-type and high-resistivity p-type CZT can be obtained by In doping, depending on the sequence of growth/annealing/cooling thermodynamic and kinetic parameters.4 One In donor in the lattice site may create a Cd vacancy and form a complex center at the nearest-neighbor site, which is the so-called selfcompensation, lowering the doping efficiency. Photoluminescence (PL) spectroscopy is a sensitive, noncontact, and nondestructive tool, suited to characterize point defects, such as substitutional impurities and intrinsic defects in CZT crystals.5–7 Temperature is an important variable in PL spectroscopy characterization.8,9 Besides the opportunity of measuring characteristic activation energies of the system through thermal quenching or enhancement processes, the appearance of additional types of recombination processes can fre-
II. EXPERIMENTAL
Cd0.9Zn0.1Te ingots were grown by the modified vertical Bridgman method (MVB). Details on the growth procedures were described in our previous work.1 Indium with the concentration of 1 × 1018 cm−3 was introduced as a dopant to compensate for the cadmium vacancies. Slices were cut along the ingots, mechanically polished, and chemically etched in turn for the PL experiments. PL was excited with a 20 mW argon ion laser working at 488 nm. The measurements were performed in the temperature range from 10 to 60 K. The In concentrations of samples were determined experimentally by using inductively coupled plasma mass spectrometry (ICP–MS). III. RESULTS AND DISCUSSION
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0163 J. Mater. Res.
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