Investigation of an Alternative Chemical Etchant for Mercuric Iodide Detectors
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INVESTIGATION OF AN ALTERNATIVE CHEMICAL ETCHANT FOR MERCURIC IODIDE DETECTORS DOMINIQUE C DAVID§, J. VAN SCYOCO, MARDIK KHUDATYAN§, R. B. JAMES§, R. J. ANDERSON§, and T. E. SCHLESINGFER> §Sandia National Laboratories, Livermore, CA 94550 'Carnegie Mellon University, Pittsburgh, PA 15213 ABSTRACT At present a 10% KI solution is commonly used as an etchant for HgI2 crystals. Recent photoluminescence (PL) spectra from such etched samples show that impurities contained in the KI solution dope the HgI2 during the etching process. Some of these dopants are known to cause carrier trapping in the detectors fabricated from the material. Thus, it is desirable to find an alternative etchant that does not create new defects in HgI2. Etchants studied here include deionized water, 10% potassium iodide (KI), methanol, and acetone. The results of acetone as an etchant reveal only small changes in the PL spectra after etching. Methanol etching causes the incorporation of a deep radiative recombination center in HgI2. INTRODUCTION Chemical etching is commonly used as a technique for preparing and cleaning the surfaces of room-temperature semiconductor materials, such as mercuric iodide. Chemical etching is very important as a surface treatment, because it removes a degraded surface layer which forms on HgI2 crystals that have been exposed to air. In device fabrication, the possibility of contamination by the processing steps (e.g., cutting and polishing) and exposure to the environment requires improved process control and care during handling. Since low-temperature photoluminescence reveals information on defects in HgI2, this technique was employed to investigate the physical changes in the near-surface region of HgI2 after chemical etching. Currently, 10% KI aqueous solution is typically used to chemically etch and polish HgI2 surfaces. This chemical treatment improves the smoothness and cleanliness of the surfaces, which is probably critical to obtaining good detector performance. Unfortunately, the use of 10% KI is not ideal for use as a chemical treatment because KI also contaminates the HgI2. Consequently, finding an alternative etchant or increasing the purity of the KI Is important to improving the manufacturing yield and state-ofthe-art for the detector technology. Several previous investigators have used low-temperature PL to study the electronic behavior of impurities, dopants, and native defects in HgI2 [1-11]. The leading motive for PL's acceptance in semiconductor materials Mat. Res. Soc. Symp. Proc. Vol. 302. @1993 Materials Research Society
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analysis is its unrivaled ability to yield information on copious amounts of defect states, as well as its relatively ease in implementation. However, the interpretation of the PL spectra of HgI2 is not always straightforward, particularly if one wants to know the identification and nature of each recombination center. Ambiguities may arise from efforts to dope the material with specified impurities, e.g., the stoichiometry can also be modified due to the presence of cont
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