Laser-stimulated compensation of bulk defects in p -CdZnTe
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ONIC AND OPTICAL PROPERTIES OF SEMICONDUCTORS
Laser-Stimulated Compensation of Bulk Defects in p-CdZnTe S. V. Plyatsko^ and L. V. Rashkovets’kyi Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Kiev, 03028 Ukraine ^e-mail: [email protected] Submitted May 12, 2005; accepted for publication May 27, 2005
Abstract—The data on the interaction of infrared laser radiation with ω Eg and power density W, no higher than the thermal destruction threshold of low-resistivity p-CdZnTe crystals (4 ≤ ρ ≤ 25 Ω cm) are presented. It is shown that the laser-stimulated defects, until attaining a stable state, pass two nonequilibrium stages depending on the interaction time and W. During these stages, the crystal properties partially relax to the initial or the stable state, respectively. In the stable state, the optical transmittance (λ ≤ 20 µm) and resistivity attain values that satisfy the requirements to the CdZnTe substrates for the HgCdTe IR photodetectors. The laser-stimulated transformations in the lattice are considered using a model that attributes the generation of activated centers in a bulk and their migration to entrainment by free carriers in an electric field of the laser wave. PACS numbers: 61.72.Yx, 81.40.Tv DOI: 10.1134/S1063782606030067
1. INTRODUCTION The CdTe and CdZnTe alloy single crystals are widely used in infrared (IR) and radiation photoelectronics. The CdZnTe alloy is most widely used as substrate for CdHgTe epitaxial layers, which are the active components of the detectors for the IR spectral range (λ = 3–5 and 8–14 µm). Irrespective of the application region, the CdZnTe should have a low-dislocation density, high optical transmittance and resistivity, and a low concentration of residual electrically active impurities. A reproducible fabrication of high-quality crystals is a very complicated problem since it is difficult to monitor the solid–liquid interface. The retrograde Te solubility in CdTe leads to the emergence of precipitates and inclusions when the crystals are cooled from the growth temperature to room temperature, and a high vapor pressure of the Cd and Zn components causes deviations from stoichiometry. One of the most important parameters, especially in the development of the rear-illuminated CdHgTe-based multicomponent focal arrays, is the optical transmittance τ of the CdZnTe substrates. Transmittance τ of the CdZnTe crystals observed in reality is lower than the highest possible τ ≈ 70% in the wavelength range λ = 1.5–30 µm, with a large spread over the wafer area and the ingot length. Low transmittance τ is mainly attributed to absorption by free carriers, specifically holes in p-CdTe [1], or with the absorption by the Te inclusions [2]. The main method in increasing τ is the heat treatment of the wafers in saturated vapors of Cd and Zn [3–5]. However, this process requires fairly high temperatures (T > 773 K) and prolonged annealing time. The result is not always satisfactory because of the changes in the chalcogen sublattice, whose vacan-
cies are a
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