Passivation of Semiconductor Surfaces for Improved Radiation Detectors: X-Ray Photoemission Analysis
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1038-O08-01
Passivation of Semiconductor Surfaces for Improved Radiation Detectors: X-Ray Photoemission Analysis A J Nelson1, A M Conway2, C E Reinhardt2, J L Ferreira1, R J Nikolic2, and S A Payne1 1 MSTD, LLNL, 7000 East Avenue, Livermore, CA, 94550 2 ENG, LLNL, 7000 East Avenue, Livermore, CA, 94550 ABSTRACT Surface passivation of device-grade radiation detector materials was investigated using xray photoelectron spectroscopy in combination with transport property measurements before and after various chemical treatments. Specifically Br-MeOH (2% Br), KOH with NH4F/H2O2 and NH4OH solutions were used to etch, reduce and oxidize the surface of unoriented Cd(1-x)ZnxTe semiconductor crystals. Scanning electron microscopy was used to evaluate the resultant microscopic surface morphology. Angle-resolved high-resolution photoemission measurements on the valence band electronic structure and core lines were used to evaluate the surface chemistry of the chemically treated surfaces. Metal overlayers were then deposited on these chemically treated surfaces and the I-V characteristics measured. The measurements were correlated to understand the effect of interface chemistry on the electronic structure at these interfaces with the goal of optimizing the Schottky barrier height for improved radiation detector devices. INTRODUCTION The development of cadmium zinc telluride (Cd(1-x)ZnxTe, CZT) as a nuclear radiation detector material has progressed with advances in CZT crystal growth that minimizes bulk defects and precipitates.[1,2] With this progress, our focus is now on surface properties of CZT since the interfacial chemistry has a powerful influence on the electrical stability of ohmic and Schottky contacts to CZT. The performance of CZT as a room temperature radiation detector can thus be improved with careful attention to modification of the surface chemistry. Chemical treatments of the CZT surface prior to application of electrical contacts require comprehensive characterization to elucidate advantageous changes in surface electronic structure. Mechanical polishing followed by bromine-based etching is routinely employed for CZT surface preparation prior to device fabrication. This treatment removes the native oxide but leaves a Te-rich surface resulting in metal/CZT interface degradation and excessive leakage currents. [1-3] Alternative surface preparation methods have been proposed for surface passivation [3-6] but have not been fully characterized nor implemented for practical device fabrication. A novel two-step chemical passivation process for CZT was reported in [4]. This paper further characterizes this chemical process in terms of the surface chemistry, surface morphology and electronic structure of chemically treated Cd(1-x)ZnxTe and correlates the results with transport properties. EXPERIMENT Device-grade unoriented p-Cd(1-x)ZnxTe was polished and subjected to various chemical treatments. Initially a 2 min Br-MeOH (2% Br) etch was performed and the resultant surface
chemistry was characterized by x-ray photoe
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