Study of Boron Implantation in CdTe
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STUDY OF BORON IMPLANTATION IN CdTe. D.N. Jamieson, California Institute of Technology, 116-81, Pasadena, CA 91125; R.C. Bowman, Jr., P.M. Adams, J.F. Knudsen, Laboratory Operations, The Aerospace Corporation, P.O. Box 92957, Los Angeles, CA 90009; and R.G. Downing, National Bureau of Standards, Gaithersburg, MD 20899. ABSTRACT The effect of large dose boron implantation in single crystal CdTe has been investigated by Rutherford Backscattering Spectrometry with channeling (RBS), double crystal x-ray diffraction (DCD) and photoreflectance spectroscopy (PR). Comparisons are made with the results of identical B implantations of Si and GaAs crystals. Multiple energy implantations were performed at roW t~mperaturl and liquid nitrogen temperature with total doses up to 1.5xl0 B ions/cm . The implanted B distribution was measured with neutron depth profiling (NDP) and found to agree well with Monte-Carlo ion range calculations. The RBS results showed that the CdTe crystals had not been rendered completely amorphous even for the highest dose implantation, unlike GaAs and Si. Furthermore, the DCD results showed little implantation induced structure in the rocking curves from the implanted CdTe crystals, in contrast 0 to GaAs. The consequences of annealing at 500 C in an attempt to regrow the crystal structure are also discussed. INTRODUCTION The II-VI compound CdTe has properties that make it useful for applications in several areas. With a direct band gap of 1.5 eV it is useful as an optical detector. In addition, CdTe is used as a substrate for the ternary compound Hg( 1 _x)CdxTe to fabricate detectors for infrared radiation [1]. CdTe crystals have also been used as high resolution room temperature x-ray and gamma ray detectors of relatively high efficiency compared to Si or Ge because of a relatively large average electron density [2,3]. Recently a novel application of large area CdTe gamma ray detectors has been proposed [4] to search for events from double beta decay candidates 114Cd, C16Cd, 128Te and 130Te. Fabrication of a CdTe FET device has been reported [5] with the possibility of monolithic integration of detectors and devices. Ion implantation could play a role in CdTe device fabrication, however Sigmon [1] points out that although the effects of ion implantation in elemental and III-V compound semiconductors are relatively well understood, this is not the case for II-VI compounds. The present work shows that the effect of B implantation into CdTe is quite different compared to Si and GaAs. B was used because of its potential use as a dopant in Hg( 1_x)CdxTe. Comparisons are also made to theoretical results from the Monte Carlo computer code TRIM [6]. EXPERIMENT Three multiple energy B implantations were done into randomly oriented single crystal CdTe samples. The experimental parameters of the three implantations are listed in Table I. The three implantations will be referred to as 'narrow RT', 'narrow LN2' and 'deep RT' where RT (nominally 293 K) and LN2 (nominally 77 K) refer to the sample temperature during
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