Diffusion of Hydrogen and Hydrogen-Dopant Interactions in Si Doped GaAs and GaAlAs Alloys
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DIFFUSION OF HYDROGEN AND HYDROGEN-DOPANT INTERACTIONS IN Si DOPED GaAs AND GaAlAs ALLOYS. J.CHEVALLIER, B.MACHAYEKHI, C.GRATTEPAIN, R.RAHBI and B.THEYS. Laboratoire de Physique des Solides de Bellevue, CNRS, 1 place A.Briand, 92195 - MEUDON, France. ABSTRACT Deactivation of silicon dopants by hydrogen in GaAs and GaAlAs proceeds through the formation of hydrogen-dopant complexes with thermodynamical and vibrational characteristics weakly sensitive to the alloy composition. However the hydrogen diffusion profile is strongly sensitive to the alloy composition. In GaAs:Si, the profile is an erfc function while in Gal-,Al 5 As:Si with x > xo, it is rather a step like function. From the doping level dependence of x,, we explain the hydrogen diffusion properties within a model where HO and H' govern the diffusion profiles respectively for x < xo and x > x 0 . We deduce that hydrogen behaves as a deep acceptor in these materials with a level slightly resonant in the conduction band of GaAs and localized in the band gap of Gal-xAlAs alloys for x > 0.07. INTRODUCTION Neutralization of silicon dopants in n type GaAs and GaAlAs alloys under hydrogen diffusion has been explained in terms of formation of hydrogen-silicon complexes [1). The existence of these complexes has been proved from the observation of local vibrational modes of hydrogen bonded to silicon donors [2]. Because H- is a diffusing species in nGaAs and n-GaAlAs [3-5], it is deduced that hydrogen behaves as a deep compensating acceptor in these materials and that the coulombic attraction between H- and the positively charged donors is at the origin of the complex formation. In this paper, we shall see how deuterium diffusion experiments in n-GaAlAs:Si with different alloy compositions and different doping levels bring information on the charge state of the dominant hydrogen diffusing species and consequently on the hydrogen acceptor level energy in these materials. EXPERIMENT In the present study, we have used three series of Gal-xAlxAs samples: - a highly silicon doped series consisting of: Bridgman grown wafers of GaAs:Si ([Si] = 1.5 x 10 18 cm' 3 ), several MBE grown Gal-xAlxAs:Si egilayers with x ranging from 0.035 to 0.15 ([Si] 8 = 1.5 x i01 cm , e = 3Mm). a series of MBE grown alloys with a fixed composition of 0.17 and containing different silicon concentrations (undoped, (Si] = 10 17 cm"3 , (Si] = 4x101 7 cm 3 and [Si] = 1.5x010 8 cm" with e = 2-3Am).
Mat. Res. Soc. Symp. Proc. Vol. 262. @1992 Materials Research Society
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- a lightly silicon doped series consisting of MBE grown epilayers with x = 0, x = 0.17 and x = 0.29 ([Si] Gal.-AlAs:Si = 2xl)T7cm"3, e = 2Mm). The composition of the alloys was deduced from electron microprobe analysis. All the samples have been exposed to a plasma in the following conditions: deuterium radio-frequency r.f. power = 0.02W/cm2 - 0.04W/cm2 , T = 215°C-240°C and t = 30 min. The deuterium diffusion profiles have been carried out on a CAMECA IMS 4f system using deuterium implanted GaAs standard for the quantification.
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