Hydrogen Complexes in III-V Semiconductors
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HYDROGEN BERNARD
COMPLEXES
IN
III-V
SEMICONDUCTORS
PAJOT
Groupe de Physique des Solides de l'Ecole Normale Sup~rieure, Tour 23, Universit6 Paris 7, 2 place Jussieu, F-75251 Paris Cedex 05, France ABSTRACT A review of the occurence, nature, structure and stability of the H complexes in III-V compounds is presented, mainly based on electrical and spectroscopical data. The importance of the problem of formation and dissociation of the complexes is pointed out and the use of H complexes in actual III-V devices is described. INTRODUCTION The importance of H complexes in semiconductors stems from the fact that some of these complexes are directly related to the electrical neutralization of the dopants and to the passivation of the recombination properties of deep centres [1,2]. Isolated hydrogen has been the model for the electronic behavior of shallow dopants (the so-called hydrogen-like centers) in group IV semiconductors. In intrinsic or n-type silicon, its closest equivalent is interstitial lithium, acting as a shallow donor with an ionization energy of 33 meV and a rather high diffusion coefficient; in p-type B-doped silicon, lithium diffuses as a positively charged ion and it can form electrically neutral pairs with negative boron ions [3]. These pairs are stabilized by electrostatic interaction and their bonding should have merely an ionic character. The bonds involving hydrogen are however stronger than those involving lithium and infrared absorption related to the stretching motion of Si-H bands in crystalline silicon [4] indicates a bonding comparable to the ones found for molecular species containing Si-H bonds. First evidence for H complexes in GaAs and GaP was obtained spectroscopically after proton and deuteron implantation [5]. Later on, it was rightly guessed that sharp IR lines observed in as-grown GaAs and InP materials between 2000 and 2300 cm- 1 were related to the presence of H complexes [6]. It was also shown that deliberate exposure of n-type GaAs:Si to H or D plasmas producing electrical neutralization of the dopant [7] gave rise to H- or Drelated lines [8), In that case, the control of the doping of the samples and the choice of the hydrogen isotope led to an unambiguous assignement and to a proposal of the hydrogen neutralization mechanism [9]. Since then, the interest for the role of hydrogen in III-V has grown considerably and many investigations have been undertaken on the physics of hydrogen in these semiconductors. This is partly due to the fact that in silicon as well as in III-V compounds, the H complexes are directly related to the neutralization of dopant atoms and to the passivation of defects as this property can be used in the fabrication of some electronic and opto electronic devices whose stability depend on dissociation kinetics of the H complexes. In this review, I will first discuss of the occurence of the H complexes. This point is directly linked to their structure and I will try to show how this structure, at least for some of them,
Mat. Res. Soc. Symp. Proc. Vol. 163.
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