Ion Implantation Damage in CdS Crystals Using RBS/Channeling and Tem
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ION IMPLANTATION DAMAGE IN CdS CRYSTALS USING RRS/CHANNELING AND TEM N.R. PARIKH, D.A. THOMPSON, R.BURKOVA AND V.S. RAGHUNATHAN Department of Engineering Physics and Institute for Materials Research McMaster University, Hamilton, Ontario, Canada, L8S 4M1 *Short term visitor from Inst. for Semiconductor Technology, Botevgrad,2140 Bulgaria; **On leave from the Reactor Research Centre, Kalpakkam, India ABSTRACT Implantation damage in single crystal of CGS produced by 60 keV Bi+ and 45 keV Ne+ at 50 K and at 300 K has been studied. Measurements of Cd disorder and dechanneliný behaviour have been made by means of RBS/channeling for He ions ranging in incident energy from 1.0 to 2.8 MeV either along or axial channeling directions. The amount of disorder measured were two orders of magnitude lower than the calculated Od disorder. Damage when analysed along the axis is larger than when analysed along the axis..Xmi values for the implanted crystals decreases as the E increases, when analysed along direction. TEM observations of Bi implanted samples show that the dislocation loops of b5 1/3 are produced. Attempts have been made to correlate the RBS/channeling results with the defect structures observed in microscopy. INTRODUCTION Cadmium sulphide, being a wide and direct band gap (2.42 ev) semiconductor, is potentially attractive for use in opto-electronic devices. It is normally either n-type or intrinsic and attempts to produce p-type semiconductor by conventional doping methods have not been successful, mainly due to a self-compensation effect which occurs at high temperatures. Attempts have been made to use ion implantation techniques to produce p-type conversion [ 1,2]. However, most of the work has concentrated on implanting different ions to improve the opto-electronic characteristics of the junction formed. Some studies of heavy ion implantation damage in CdS crystals using Rutherford Backscattering (RBS)/channeling [31 and TEM [4] have been carried out. However, the results of these two techniques have not been correlated. In t~is work, we have studied implantation damage due to 60 keV Bi and 45 keV Ne at 50 K and at 300 K analysed using the RBS/channeling technique with 1.0 to 2.8 MeV He ions, E , incident either along the or the . TEM observations +have been made of unimplanted CdS and CdS crystals implanted with 60 keV Bi . The results of these two techniques have been correlated to identify defects produced by ion implantation. EXPERI MENTAL CdS crystal (wurtzite structure - see Fig. 1) of high resistivity were obtained commercially, with surfaces parallel to either {0001} or {1120}. The crystals were polished chemically with dilute HCI (1HCl:lH 0) on acid resistant cloth for -5 min. to remove damaged layers caused either by mechanical polishing or prior implantation. The value of xmin (the ratio of the aligned to the nonaligned yield of" RBS Spectra) was -5% at 300 K. A detailed description of the experimental set-up is_(escribed in ref. [51. The base pressure in the target chamber was < 10 Torr. The sample was
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