Surface Morphology and Photoluminescence Spectra of ZnSe (Na) After Excimer Laser Annealing
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SURFACE MORPHOLOGY AND PHOTOLUMINESCENCE SPECTRA OF ZnSe (Na) AFTER EXCIMER LASER ANNEALING *
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GUAN-JIUN YI, G F. NEUMARK , Z. LU#, P.R. NEWIURY C.F. YU B.J. FITZPATRICK , M. SHONE , and A. SICIGNANO-. *Columbia University, Henry Krumb School of Mines, New York, NY 10027 #Columbia University, Dept. of Electrical Engineering &Columbia University, Dept. of Applied Physics; Philips Laboratories Fellow @Philips Laboratories, Briarcliff Manor, NY 10510 ABSTRACT We have investigated excimer laser annnealing of Na doped ZnSe, with emphasis on photoluminescence (PL) characterization as a probe of resultant changes in materials properties. We observed a relative increase, after annealing, of Na on substitutional (acceptor) sites vs. Na on interstitial (donor) sites. Another result was the occurrence of extensive twinning; unfortunately such twinning has complicated the analysis of other changes. INTRODUCTION Laser processing has developed into an important technique for impurity incorporation into semiconductors. A particularly attractive feature of this method is that one can achieve non-equilibrium concentrations, i.e. one can exceed the solubility limit [e.g. 1]. This feature is of particular interest for wide-band-gap semiconductors, since it has recently been shown [2] that equilibrium solubilities are very likely to be quite low in such materials. A material of considerable interest for opto-electronic applications is ZnSe, and it thus appears fruitful to investigate laser processing of this material. There is of course an immediate question in use of such laser processing: can one obtain a temperature high enough for adequate (probably non-equilibrium) impurity incorporation with little or no surface decomposition? This problem would be expected to be particularly severe in a material such as ZnSe, which has a high vapor pressure [3]. It is well known that short pulses tend to minimize decomposition [4], and for this reason we selected excimer lasers. An independent study by Bokhonov et al. [5], on not deliberately doped ZnSe, also used such excimer lasers, and studied some changes in the PL; however, it gave only a few brief results on the PL in the exciton region, and a few comments on the observation of extensive twinning. In the present work we studied ZnSe(Na), and include the changes of PL at longer wavelengths, with particular focus on the donor-acceptor pair (DAP) PL. Both DAP and exciton spectra can be very useful probes of material properties (for a general review on PL, see for ex. [6]). The present study focused on ZnSe(Na), since the effect on the PL of this dopant has been well established both for the bound exciton spectra [7] and the DAP bands [8]. As regards these DAP bands, it has been shown [8] that Na on the interstitial site (NaI) gives a characteristic high-energy shoulder on the (more usual) DAP peak of the Group III substitutional donors (where Na on the Zn site - Na Zn - is the acceptor for either donor). This thus provides a "marker" for the Na site. For convenience, we will discuss the
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