Mapping of Defects in Metal-Semiconductor-Metal (MSM) Detectors in Hg 1-x Cd x Te by Nuclear Microprobe
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MAPPING OF DEFECTS IN METAL-SEMICONDUCTOR-METAL (MSM) DETECTORS IN Hgl-xCdxTe BY NUCLEAR MICROPROBE PATRICK W. LEECH*, SEAN P. DOOLEY** and DAVID N. JAMIESON** *Telecom Australia Research Laboratories, Clayton, 3168, Victoria, Australia. "**MARC,School of Physics, University of Melbourne, Parkville, 3052, Victoria, Australia.
ABSTRACT: The incidence of compositional and structural inhomogenieties in MSM detectors based on Hgl-xCdxTe/GaAs and Hgl-xCdxTe/GaAs/Si has been examined by nuclear microprobe. With a 2 MeV He+ beam focussed to •.5 grm, the microprobe has demonstrated the capability for RBS channelling in the active region of a Hgl-xCdxTe device and the imaging of defects by Channelling Contrast Microscopy (CCM). A series of linear growth defects in some Hgl_ xCdxTe devices were identified using CCM. The channelling RBS spectra from these regions have shown an increase in Xrin compared with the surrounding high quality crystal. The occurence of these defects was associated with a degradation in the performance of affected devices in an array. RBS spectra have also revealed the presence of an anomalous CdTe layer, correlating with a significant reduction in dark current and increase in breakdown voltage of these devices. RBS channelling of individual devices has identified differences in Xmin between arrays which were prepared under equivalent conditions of growth and processing. INTRODUCTION: Structural defects and compositional inhomogenieties in Hgl~xCdxTe are major obstacles to improvement in the manufacturing yield of infrared detectors. As a consequence, the identification of defects in both wafers and in devices has been pursued by several techniques. Synchrotron x-ray topography was used in the mapping of defects in epitaxial layers of Hgl-xCdxTe and then correlated with the performance of an array of infrared detectors manufactured on the wafer [1]. Alternatively, electron beam induced current (EBIC) [2], optical beam induced current (OBIC) [2] and laser beam induced current (LBIC) [3] were successful in the imaging of defects in fabricated p/n junction diodes. Also, IR absorption has been used to monitor the incidence of microstructural inhomogenieties and defects in relation to the quality of p/n diodes [4]. But while these techniques have enabled the recognition of specific types of macrodefects, they lack the capability for the analysis of local composition or crystal quality of individual devices. The nuclear microprobe has shown the potential for RBS channeling in the active region of a device and the imaging of defects by Channeling Contrast Microscopy (CCM). Using a 2 MeV He+ beam focused to 5 gtm or less, the microprobe has previously analysed the micron-scale features in layers of Hgl_xCdxTe deposited by metalorganic chemical vapor deposition (MOCVD) [5]. In this paper, a correlation has been made between the electrical characteristics of metalsemiconductor-metal (MSM) detectors on Hgl-xCdxTe/GaAs or Hgl-xCdxTe/GaAs/Si and the incidence of structural defects revealed by nuclear microprobe.
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