H States, Impurity Passivation and Gettering Studies in H-Implanted SI Crystals
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H STATES, IMPURITY PASSIVATION AND GETTERING STUDIES IN H-IMPLANTED SI CRYSTALS Bulat N. Mukashev and Serikbol Zh. Tokmoldin Physical Technical Institute, Kazakh Academy of Sciences, 480082, Alma-Ata, Republic of Kazakhstan ABSTRACT IR and DLTS studies of H-implanted Si crystals are performed. It is shown that H is a bistable impurity: it has an equilibrium site at a T-site 0 for H+ and H- and at a BC-site for H . The mechanisms of H-Passivation of defects and shallow and deep impurities are discussed. INTRODUCTION A qreat interest in the studying of H states in semiconductors is caused owinq to the ability of H to neutralize defects and impurities (1]. In this paper we present the results of IR and DLTS studies of H states in H-implanted Si and of interactions of H with defects and impurities. Si crystals with different concentrations of shallow acceptors and donors (we label these impurities by the letters B and P. respectively) as well as of transition metals (TM) and sulfur (S) were used. THE STATES OF A SINGLE H IN SI The modern theory [2] predicts that the equilibrium H site in Si is a bond-centered (BC) site, whereas a tetrahedral (T) site is metastable. This point of view was confirmed by electron and muon spin resonance [3,4] and channeling [5]. The drift of H* and H- in the electric field (6] indicates that H has both acceptor and donor levels in the qap. The calculations [2] show that the equilibrium H+ and H- sites are BC- and T-sitesrespectively. Accordinq to the data on H diffusion in n-Si and p-Si [7],the donor and acceptor levels of H were expected to be situated close to the middle of the qap. However, DLTS studies of H states in n-Si [8,9] and the precise analysis of the data on H diffusion in heavily-doped p-Si [10] show the presence of two different positions of the donor H level: at about Ec -0.16 eV in nSi and at about Ev+0.3 eV in p-Si. This fact indicates that there is an unknown state of H, different from H13c . Takinq into account the data on the drift of H+ in the electric field, one can proposed that this unknown state of H is a proton at an interstitial T-site. Fiq. 1 shows IR spectra of Si:P and heavily-doped Si:Sb and Si:B, implanted by protons and deuterons. The analysis [11] show that the bands labelled h, d, t and s are related to vibrations of H* and H_ in the vicinity of V HiH*and P+H- and of H* (fiq. 2). 2 T d, t, s and h show the different dependence upon the Fermi level (E F position: d and t are not observed at Ev < Ec -0.2 eV, s disappears at Er > E +0.3 eV and h is observed at E +0.3 eV < E
< Ec-0.
2
eV.
The EF dependence of d and t indicates that firstly P+Hat EF < Ec -0.2 eV and secondly there is the P+H- decay due to
not appears interactions
with minority carriers creatinq durinq implantation. Because H has an acceptor level in the qap (6J, one can conclude that this level is related to H-/H 0 and situated near E -0.2 eV. c T T Mat. Res. Soc. Symp. Proc. Vol. 262. @1992 Materials Research Society
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d t
xO.5
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2
Fiqure 1. New H-related local vibrational ba
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