Photoluminescence Detection of Native Defects in The Surface Region of Bulk CdTe
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PHOTOLUMINESCENCE
DETECTION OF NATIVE DEFECTS IN THE SURFACE REGION OF BULK CdTe
P.M. AMIRTHARAJ AND N.K. DHAR U.S. Army Center for Night Vision and Electro-Optics Fort Belvoir, VA-22060 ABSTRACT The native defects introduced by Br./CH3 OH etching and aging under atmospheric conditions have been investigated in In doped, bulk CdTe using photoluminescence (PL) spectroscopy. The results indicate a large enhancement of the Cd vacancy related 1.5896 eV excitonic feature with chemical treatment and aging. Hence, the primary perturbation is interpreted to be a small loss of Cd within the sampling region. This result is compared and contrasted with previous studies of etching induced modifications. The implications of Cd depletion on interpreting PL spectra, device processing and long term stability are considered. INTRODUCTION The presence of native defects such as vacancies, interstitials, etc. can have a significant influence on the electronic behavior of semiconductor materials. However, detection of specific defects and studying their microscopic properties is nontrivial. The traditional methods of microscopic chemical detection is inapplicable; and an indirect study of properties such as the transport behavior lacks sufficient information on both the microscopic details and spatial resolution. Photoluminescence (PL) spectroscpopy, in comparison, is almost ideal for this study since sharp well defined optical features associated with many native defects can be investigated with acceptable spatial resolution. It is the intent of this paper to provide examples of the applicability of PL: the results of an investigation of the native defects introduced as a result of chemical treatment and aging in CdTe are presented. The results are also important in improving the capability of PL in the analysis of defects in CdTe since it identifies those features introduced as a result of the modification of the surface region. Chemical etching is widely used for cleaning semiconductor surfaces and in processing applications. Deleterious effects may be caused as a result and hence, it is important to understand the consequences to the near surface region and perturbations in the physical properties of the sample. Several previous investigators have used photoluminescence (PL) to study the electronic behavior of impurities, dopants and electrically active native defects in CdTe [1-12]. However, the results can be ambiguous. Residual impurities, self compensating native defects [2] and those introduced as a result of the chemical treatment may interfere with the interpretation. A large proportion of the published results on bulk CdTe used surfaces that were chemically etched, the most common etchant being a solution of Br 2 and CH OH with concentrations in the range of 0.1 to 20% by volume. It is well known that Br 2 /CH 3 OH Mat. Res. Soc. Symp. Proc. Vol. 161. @1990 Materials Research Society
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leads to a preferential loss of Cd from the surface region [1416]. In comparison to earlier conclusions, the results of this study str
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