Pulsed Laser Annealing of Zirconia Capped, Native Oxides Free GaAs Surfaces
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PULSED LASER ANNEALING OF ZIRCONIA CAPPED, NATIVE OXIDES FREE GaAs SURFACES D. PRIBAT, L.M. MERCANDALLI, M. CROSET and 3. SIEJKA* Thomson-CSF/LCR, Domaine de Corbeville, B.P. 10, 91401 Orsay Cedex, France. *Groupe de Physique des Solides/ENS, Tour 23, 2 Place Jussieu, 75221 Paris, France. ABSTRACT We have studied the effects of pulsed laser irradiation on silicon implanted, thermally activated , Calcia Stabilized Zirconia (CSZ) capped GaAs substrates. Reference substrates have also been irradiated in air for comparison. CSZ as a solid electrolyte has been used to chemically reduce the GaAs surface native oxides prior to irradiation while maintaining the surface stoechiometry. Our results indicate a spectacular decrease in defect density after laser irradiation of the CSZ capped-native oxide free samples, as compared to the samples irradiated in air. I. INTRODUCTION Important oxygen incorporation from native oxides layers has recently been evidenced in pulsed melted GaAs material III. It has also been reported that oxygen implantation in Silicon doped GaAs layers resulted in free carrier compensation, even after thermal annealing at temperatures up to 900 0 C 121. Berth et al. 121have suggested that the observed carrier compensation was likely to originate from Si-O complex formation during annealing, these complexes being either deep acceptors or electrically neutral. A dose of 10,3 oxygen atoms/cm 2 was sufficient to totally compensate 3.1012 implanted silicon atoms/cm 2 (with a peak concentration of 1.5.10 1 7 /cm 3 ) in undoped semi-insulating GaAs substrates 121.Considering the results of both refs. 1 and 2, it is logical to suspect that the oxygen incorporation from native oxides layers can play a significant role in carrier compensation observed after laser irradiation of homogeneously silicon doped GaAs 131. Therefore it is worth investigating the effects of laser irradiation on the electrical properties of silicon doped GaAs layers free of native oxides. Moreover, in order to eliminate or at least minimize defect creation due to As evaporation during laser annealing - which could partially mask the effect due to the absence of oxygen - the experiments have to be performed under capping conditions. Hence, two requirements must simultaneously be met: (:) the GaAs surface has to be capped and (i0) it has to be native oxides free. In order to fulfill the above conditions, we propose an original way, consisting in the use of Calcia Stabilized Zirconia (CSZ) thin films. CSZ is a solid electrolyte allowing oxygen movement while blocking the migration of As and Ga atoms. In a first step the CSZ film is used to chemically reduce the GaAs native oxides in flowing H2 . Schematically, the chemical reduction of native oxides originates from the difference in oxygen chemical potential between both sides of the CSZ film (native oxides and reducing external medium). An oxygen flux appears thus through the CSZ film as long as the two oxygen chemical potentials on both sides of the film are not equal. Details are given in ne
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