Effect of stress on defect transformation in B+ and Ag+ implanted HgCdTe/CdZnTe structure

Ion implantation in HgCdTe (MCT) is a commonly used method for fabricating IR sensitive photovoltaic devices. It is well known that ion implantation induces mechanical stress in HgCdTe layers, which is a matter of paramount importance for solid-state devices, and has been exploited to improve their electrical and optical properties. It was shown that implantation-induced stress is an important factor influencing the depth of p-n junctions in MCT-based structures [1]. Moreover, existence of the built-in electric field in the strained MCT-based heterostructure results in the spatial separation of the nonequilibrium carriers and in the possibility of room temperature detection of the IR radiation [2]. We have analyzed the properties of HgCdTe/CdZnTe structures implanted with B+ and Ag+ with an ion energy of 100 keV and dose of 3x1013 cm-2. The annealing was performed for 5 hours in argon atmosphere with upward pressure of 4 bars. The surface morphology as well as optical, mechanical and electrical properties of heterostructures were studied. The software package TRIM_2008 was applied for the mathematical modeling of ion implantation. The structural properties of the MCT-based structures were analyzed using double and triple crystal x-ray diffraction to monitor the disorder and strain of the implanted region as a function of processing conditions. The transformation of the defect structure of a radiation-damaged MCT layer and profiles of implanted dopant during annealing were investigated. It was found that the implantation of elements with different ionic radiuses, such as B and Ag, leads to the formation of layers with significant difference in thickness and damage character, as well as with maximum mechanical stresses that differ by two orders of magnitude. It was established that a surface region of radiation-induced point defects 100 nm and 400 nm thick is formed in the Ag and B implanted samples, respectively. Formation of the nano-scale islands was also found on the surface of the Ag implanted HgCdTe samples. 1. H. Ebe, M. Tanaka and Y. Miyamoto, J. Electron. Mater. 28, 854 (1999). 2. T. Kryshtab, R. Savkina, F. Sizov, A. Smirnov, M. Kladkevich and V. Samoylov, Phys. Stat. Sol. (c) 9, 1793 (2012).