Germanium Extremely Heavily Doped by Ion-Implantation and Laser Annealing: A Photoluminescence Study
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GERMANIUM EXTREMELY HEAVILY DOPED BY ION-IMPLANTATION AND LASER ANNEALING: A PHOTOLUMINESCENCE STUDY M. CARDONA J. WAGNER, G. CONTRERAS+, A. COMPAAN+, Max-Planck-Institut fir Festk6rperforschung, Heisenbergstr. 1, D - 7000 Stuttgart 80, Federal Republic of Germany and A. AXMANN Fraunhofer-Institut ffir Angewandte Festk6rperphysik, Eckertstr. 4, D - 7800 Freiburg, Federal Republic of Germany ABSTRACT It has been shown previously that dopant concentrations far above the equilibrium solubility limit can be obtained in semiconductors by pulsed laser annealing of heavily ion implanted material. We exploit this fact to study the photoluminescence of germanium with dopant concentrations up to 1021 cm-3. From this study we obtain information of higher lying band minima and the on the filling shift of the optical band gap as a function of carrier concentration over a much wider range than accessible with bulk doped material. In addition it is shown that photoluminescence provides a diagnostic tool to characterize implanted layers. INTRODUCTION Previous work [I1 has shown that pulsed laser annealing of heavily ion implanted semiconductors can be used to achieve concentrations of donors or acceptors far above the solubility limit. For bulk doped material the substitutional3 impurity by the equiconcentration is typically limit to 10 1 9 -10 2 0 cmIn ion implanted and laser annealed librium solubility limit. samples, however, White et al. [ 1] have shown that impurities in concentrations well above 1021 cm- 3 can be incorporated on substitutional lattice sites. The effect of heavy n- or p-type doping on the electronic properties of a semiconductor can be described in terms of a reduction of the band gap and a filling of the conduction or valence band. [ 21 By photoluminescence (PL) experiments this can be studied via the radiashift as well as the band filling The tive recombination of photoexcited minority carriers. [ 3] low energy edge of the luminescence band gives the position of the reduced gap E while the high energy cut-off indicates which is the sum of EG2 and the Fermi the optical gap E G, 1 Thus the carri6r distribution, energy due to bang' filling. which determines the electrical properties of a semiconductor, is monitored by the PL spectrum. In this paper we present the results of a photoluminescence study of ion implanted laser annealed Ge with impurity In both n- and p-type samples concentration up to I 01 cm-3. we find luminescence which originates from the recombination of minority carriers which are not thermalized in their band. The PL technique as a diagnostic tool to characterize ion im+DAAD Fellow, on leave from E.S.F.M.-I.P.N. M~xico ++Von Humboldt Foundation Fellow, on leave from Kansas State University, Dept. of Physics, Cardwell Hall, Manhattan, Kansas 66506, U. S. A. Hat.
ms. Soc. Symp.
Proc. Vol. 23 (1984)@Elsevier science Publishing Co., Inc.
148
Photon Energy (eV)
Photon Energy (eV)
075
08
085
09
10
1.8
11
5K hVLoser= 1.92 eV
Ge: P
TBath
0
2.0
Ge P
4.10
04'
16
P*/cm
2.4
2.6
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