Long Range Coulomb Effects on Hydrogen Debonding from Boron Acceptors in Silicon
- PDF / 368,235 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 58 Downloads / 155 Views
LONG RANGE COULOMB EFFECTS ON HYDROGEN DEBONDING FROM BORON ACCEPTORS IN SILICON* R. A. ANDERSON AND C. H. SEAGER Sandia National Laboratories, Albuquerque,
NM 87185
ABSTRACT Previous work has demonstrated that B-H pairs in silicon thermally dissociate obeying simple first order kinetics if they are located in a region depleted of majority carriers. B.H debonding in equilibrium, We have investigated the is a slower, more complex process. however, dissociation of B.H pairs under a variety of equilibrium and non-equilibrium conditions and have demonstrated that the dissociation process is strongly In influenced by the local concentration of majority and minority carriers. particular, we show that injection of minority carriers can markedly accelerate the dissociation process. A model is proposed which suggests positive, must that hydrogen released from an acceptor, while initially always be neutralized before escape is possible. This picture correctly describes the time dependence of debonding in equilibrium, and it predicts the enhanced debonding in forward biassed diodes provided the characteristic time for H charge conversion is long.
INTRODUCTION A positive charge state for hydrogen in silicon is well established experimentally [1-3], but recent data [2,4-6] have given strong evidence that neutral, mobile, H interstitials are also prevalent. The energy level of the HO/H+ transition is not really known nor are the lattice sites for H in either charge state. While bond-centered (b.c.) H is unequivocally favored as the minimum energy site by various theoretical calculations [7-12], the large lattice distortions associated with this configuration suggest that there may be a substantial activation barrier for forming b.c. hydrogen, leaving open the possibility that the high mobility paths for H diffusion proceed through tetrahedral sites where the hydrogen is not tightly bound. The structural model for H-acceptor pairs first suggested by Pankove et al. [13] seems well established by infrared spectroscopy [14] and channelling measurements [15,16]. In this picture the hydrogen is located at a bond centered position next to the acceptor. However, there exists some uncertainty about the kinetics of H-acceptor dissociation. Zundel et al. [3,17] have shown that reverse-bias-annealed hydrogenated Schottky diodes doped with B, Al, Ca, and In display a simple first order kinetic behavior consistent with:
a(AH at
-k(A.H)
(1)
where (A.H) is the concentration of acceptor/hydrogen pairs. The dissociation rate, k, is thermally activated with 1.3 to 1.4 eV, rather independent of the acceptor atom. These same authors also demonstrated that hydrogen was field driven to deeper depths after dissociation consistent with a positive charge state of H, and that virtually all debonded hydrogen became bonded to acceptors deeper in their diodes [3,17]. Annealing experiments carried out on unbiassed diodes [18] have yielded a much different, slower, kinetic behavior than given by Eq. (1). Zundel et al. [18] attributed this to the effects
Data Loading...
