Infrared Studies of the Double Acceptor Zinc in Silicon
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INFRARED STUDIES OF THE DOUBLE ACCEPTOR ZINC IN SILICON A. Dbrnen , R. Kiexjle , K. Thonke , P. Stolz , G. Pensl , D. Grinebaum ang N.A. Stolwijk ..4. Physikalisches Institut, Universitdt Stuttgart,D-7000 Stuttgart 80, FRG .. Institut fOr angewandte Physik, Universit~t Erlangen, D-8520 Erlangen, FRG Institut fOr Metallforschung, Universit~t MLnster, D-4400 MOnster, FRG
ABSTRACT In the present paper, optical absorption studies on the neutral charge state of the double acceptor zinc in silicon are presented. Measurements were carried out in the mid infrared (MIR) and in the near infrared (NIR) region. The MIR absorption spectra show the excitation series of an effective-mass0 like hole, from which the Zn level position is calculated to be at Ev + 319.1 meV. A splitting of the ground state into 3 sublevels is assigned to hole-hole coupling and crystal-field splitting. Absorption spectra obtained 0 in the NIR are interpreted in terms of an A X-type bound exciton.
INTRODUCTION Double acceptors in germanium are widely investigated by means of optical spectroscopy [1]; but detailed information on double acceptors in silicon is still rare. Beryllium e.g. introduces several centers when it is diffused into silicon [2,3]. One of these centers (BeI), is believed to be the substitutional Be double acceptor [2,3] though a second charge state has not yet been reported 14]. The only double acceptor in silicon identified so far is zinc. Two levels at Ev + 0.31 eV and Ec - 0.55 eV are identified with the 0/- and -/-charge state transitions, respectively [5,6]. In recent work the thermal-emission rates and capture rates of carriers were characterized by transient-capacitance technique [7,8]. Optical investigations were dealing with photoionization only, so that still some uncertainty remained about the exact level positions [9,101. By observation of effective-mass-(EM)-like excited states of the Zn° center, we are able to calculate precisely the ground state to be 319.1 ± 0.3 meV above the valence band. In a second part, spectra, obtained in the NIR spectral region, are discussed with regard to excitons bound to Zn°.
EXPERIMENTAL 13
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Samples from boron doped float zone material (10 cm ) and phosphorus 5 3 doped Czochralski crystals (2.10Iscm-3 and 4.10 cm ) were prepared for the zinc diffusion. Samples were sealed in evacuated quartz ampoules together with zinc ingots and heated to 12000C for 40 hours. The diffusion was finished by quenching the ampoule in water. An additional heat treatment at 0 600 C was applied, to move most of the incorporated zinc atoms into the double acceptor configuration. Optical surfaces were achieved by polishing. A Fourier spectrometer (Bomem DA3 series) was used to record the absorption spectra. The setup was equipped alternatively with a cooled InSb detector for the MIR and with a germanium diode for the NIR. 106 The-3 zinc concentration was determined by Hall measurements to be (9±3)* 10 cm . Spreading resistance profiles were taken on similarly treated samples to control the zinc distribution.
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