Raman Studies of Znse Lattice Damage and Recovery Due to N Implantation and Annealing
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RAMAN STUDIES OF ZnSe LATTICE DAMAGE AND RECOVERY DUE TO N IMPLANTATION AND ANNEALING
A. Deneuvillea,c, P. Ayyubd, C. H. Parkd, T. Andersond, K.S. Jonesc and P. H. Hollowayc, University of Gainesville, FL 32611.
P. Lowenc, Florida;,
ABSTRACT The "bulk" and near-surface regions of N implanted heteroepitaxial ZnSe films were studied using the full width at half maximum (FWHM) of the LO phonon Raman line. The "bulk" FWHM has a minimum below an annealing temperature Ta = 4000C, and increases for higher Ta. This is attributed to the relaxation of residual stress, and to an increased stress from the formation of Zn vacancies. The surface FWHM has a deep minimum near Ta = 500 0 C which is attributed to the relaxation of the implantation damage at lower Ta, and stress induced by Zn vacancy formation at higher Ta. Another wider peak is found just after implantation and for Ta = 6000C, and results from a sum of two peaks attributed to the heavily damaged region around Rp and to the region with Zn vacancies. INTRODUCTION From its bandgap width (2.7 eV), ZnSe is a promising material for blue emitting devices. However, problems still remain in achieving a sufficient level of p-type doping[l]. Ion implantation of N [2a,2b], Li (2c] and Na [2d] have been tried for doping. However a preferential loss of Zn can occur during the annealing process [2,3]. In Si or III-V compound semiconductors, the implantation damage and its recovery have been monitored through the evolution of a Raman line [4]. Since the escape depth of the light depends on its energy, the excitation energy, E, must be chosen to probe mainly the outer damaged part of the film. We report here on the effects of N implantation and rapid thermal annealing (RTA) under Zn overpressures through the evolution of the full width at half 1 maximum (FWHM) of the LO phonon (252 cm" ) Raman line of ZnSe. We probe both the "bulk" and the near-surface (damaged) part of the film using different wavelengths of light. EXPERIMENTAL Films of ZnSe 2 pm thick were grown by molecular beam epitaxy on undoped (100) GaAs substrates at 275*C and a Zn to Se beam flux ratio of 1:2. The N atoms were implanted with an energy of 110 keV and a fluence of 7x101 cm"2 at room temperature. The N concentration is expected to be approximately Gaussian with a maximum at Rp = 2000A and ARp =
900A.
With these light
damage is
implanted atoms,
the main
(nuclear)
expected to have about the same profile as that of the
Mat. Res. Soc. Symp. Proc. Vol. 209. 01991 Materials Research Society
458
N species. Rapid thermal annealing was performed between 400 and 600 0 C under the Zn partial pressure for the temperature Ta. The Raman spectrum was excited by the 5145A (400mW) and the 4578A (20 mW) lines of an argon laser with a resolution of =2 cm-. In the following, the FWHM will not be corrected for the instrumental linewidth. The Raman signal has a depth modulation given by exp (-2ad) where a is the absorption coefficient of ZnSe at E. The signal can originate mainly form the volume in the sample which ha
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