Lattice sites and damage annealing of Er in low-dose implanted GaAs

Abstract

We have used conversion electron emission channeling to determine the lattice location of 167m Er (t 1/2 =2.28 s) in GaAs after 60 keV room temperature implantation of 167 Tm (t 1/2 =9.25 d) at low doses (0.6-3×10 13 cm -2 ). Following a recovery step of the implantation damage at 200-300°C, we observe a large fraction of Er (45-68%) on substitutional Ga sites. A second fraction of Er is found on the T As sites (the tetrahedral interstitial sites with nearest As neighbours). The fraction on T As sites reaches a maximum of 12-23% following annealing at 500-600°C. At higher annealing temperatures the channeling effects decrease markedly, which we attribute to the well-known degradation of GaAs due to As evaporation. . In general, the optical activity of Er is closely related to its lattice site and immediate surroundings. For Er in GaAs, theoretical investigations suggest that isolated Er prefers substitutional Ga sites (S Ga ) and that even the interaction with additional native defects such as Ga i , As i , or V As is hardly able to remove it from this site [2]. Er on tetrahedral interstitial sites (T) is considered to be metastable, and the T As sites should be lower in energy than the T Ga sites. On the experimental side, a number of Rutherford backscattering (RBS) lattice location studies on GaAs:Er revealed the following trends. In general, samples doped with Er during metalorganic chemical vapour deposition (MOCVD) [3][4][5][6] or molecular beam epitaxy (MBE) [7][8][9] showed the majority of Er in neartetrahedral interstitial locations with respect to the GaAs lattice. A discrimination between T As and T Ga sites, however, was not considered in any of these studies. Er concentrations in these samples varied in a wide range from 10 17 cm -3 to 7×10 20 cm -3 . The interstitial-like Er location in the high-dose regime was related to the formation of ErAs precipitates growing epitaxially along the GaAs <100> directions. In the low-dose doped samples, on the other hand, the interstitial position was ascribed to complexes between Er and carbon, which is a frequent contaminant in MOCVD. Samples which were intentionally co-doped with oxygen during MOCVD growth, however, showed mainly near-substitutional Er [6,10].Less studies have dealt with the lattice location of implanted Er in GaAs. Following high-dose implantation at 250°C (10 15 cm -2 at 150 keV, peak concentration of 2.8×10 20 cm -3 ) and annealing up to 1000°C, Er atoms were found within the <100> but partly outside the <110> atomic rows [11,12]. While such a behaviour could be due to a mixture of substitutional (S) and tetrahedral interstitial (T) Er, it would also be expected for Er within large <100> epitaxial ErAs precipitates. Only the outermost Er atoms in the precipitates sense the particle flux-peaking within the <110> channel, at the same time they shadow the Er atoms in deeper ErAs layers [10]. Recently the Er sites following implantations at lower doses (0.75-7.5×10 14 cm -2 , 100-250 keV, ≈1019 -10 20 cm -3 ) and annealing at 850°C were ...

Mössbauer study of Fe in GaAs following 57Mn + implantation

“…This assignment is consistent with Mössbauer measurements on 119 Sn implanted GaAs where the spectra observed at high temperature implantations were dominated by a single line component which on the basis of its Debye temperature and dramatic increase of intensity with annealing temperature was assigned to Sn on substitutional Ga sites [5,6]. Lattice location of studies on Mn, Cr, Zn and Er atoms in GaAs [1][2][3][4] also support this assignment. …”

“…Lattice location studies on low dose ion-implanted GaAs identify the majority of implanted ions at substitutional Ga sites [1][2][3][4]. Mössbauer studies on 119 Sn m implanted GaAs [5,6] have identified four components in the spectra attributed to Sn atoms on undisturbed substitutional Ga sites, a small interstitial fraction, and to Sn in two vacancy related defect structures.…”

Stability and diffusion of interstitial and substitutional Mn in GaAs of different doping types

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