Direct Evidence for Tetrahedral Interstitial Er in Si

Abstract

We report on the lattice location of Er in Si using the emission channeling technique. The angular distribution of conversion electrons emitted by the decay chain 167 Tm ͑t 1͞2 9.25 d͒ ! 167m Er ͑2.27 s͒ was monitored with a position-sensitive detector following room temperature implantation and annealing up to 950 ± C. Our experiments give direct evidence that Er is stable on tetrahedral interstitial sites in float-zone Si. We also confirm that rare earth atoms strongly interact with oxygen, which finally leads to their incorporation on low-symmetry lattice sites in Czochralski Si. [S0031-9007(97) Rare earth doping of Si is known to result in the formation of luminescent centers and is considered as a possible way to manufacture Si-based optoelectronic devices [1]. Among the various rare earth elements, Er is of special interest since its atomic transition at 1.54 mm matches the absorption minimum of SiO 2 , a highly desirable feature both for signal transmission through glass fiber cables and optical on-chip communication. Luminescence at this wavelength from Er-implanted Si was already established several years ago [2]. Meanwhile Er-based light-emitting diodes operating at room temperature have been reported [3]. The basic understanding of Er luminescence in Si, however, is far from complete. This concerns both the lattice sites of Er and the role of codopants such as O, N, or F, which were found to have a beneficial influence on luminescence yield. Photoluminescence (PL) spectroscopy studies have identified a number of Er-related centers with different crystal surroundings in Si [4]. The most intense PL yield was due to two centers having cubic and axial symmetry, respectively. While the cubic center occurred in both float-zone (FZ) and Czochralski (CZ) Si and was attributed to tetrahedral ͑T ͒ interstitial Er, the center with axial symmetry was observed only in CZ Si and ascribed to Er-O complexes. The existence of tetrahedral interstitial Er would be also in agreement with theoretical studies, which predict that T sites are the most stable sites for all oxidation states of isolated Er atoms in Si [5]. Direct lattice location using the Rutherford backscattering (RBS) channeling technique only suggested substitutional [6] or hexagonal ͑H͒ interstitial Er [7,8]. The reasons for these discrepancies, however, are unclear.To study the lattice sites and damage recovery after rare earth implantation, we have applied conversion electron emission channeling [9] combined with position sensitive detection. Emission channeling makes use of the fact that charged particles emitted from radioactive isotopes in single crystals experience channeling or blocking effects along low-index crystal directions. This leads to an anisotropic particle emission yield from the crystal surface which depends in a characteristic way on the lattice sites occupied by the emitter atoms. While this technique as such is not new and, in case of rare earths, was already used once for the lattice location of 175 Yb in Si [10], we have for the fi...

Electron paramagnetic resonance and photoluminescence study of Er-impurity complexes in Si

“…29 These calculations were performed for Er incorporated into pure silicon with no extra impurity present. Furthermore Wahl et al 30 have recently experimentally demonstrated, by the emission channeling technique, that Er is in a tetrahedral interstitial site in float zone Si. A value of xϭ0.35 would imply that the crystal-field ground state has a ⌫ 6 representation and a single sharp isotropic EPR spectrum with a g value of 6.8 would be predicted.…”

Electron spin resonance of Er–oxygen complexes in GaAs grown by metal organic chemical vapor deposition

“…Knowledge of the microscopic structures of the rare earth impurities in semiconductor hosts is very important for fabricating efficient injection-type light emitting devices. To understand the microscopic structures, the electron spin resonance ͑ESR͒ measurements, [1][2][3][4][5][6][7] the extended x-ray absorption fine structure ͑EXAFS͒ measurements, 8,9 and the Rutherford backscattering ͑RBS͒ channeling measurements [10][11][12][13] have been performed on Er-doped GaAs, Er-doped Si, and Yb-doped InP.…”

The influence of oxygen on the lattice sites of rare earths in silicon

“…Following implantation of 167 Tm with doses from 6×10 12 to 5×10 13 cm -2 and annealing at 600°C, we find the majority of 167m Er on near-tetrahedral interstitial (T) sites in both FZ and CZ Si [5,6]. For FZ Si, in-situ measurements at 900°C give direct evidence that 167m Er even resides on these sites at that temperature [7].…”

“…While the exact mechanisms of how O enhances the luminescence yield of Er are still a matter of debate, the binding of O to Er can be regarded as well-proven. As a complementary technique to EXAFS and TEM we use conversion electron emission channeling from the radioactive nucleus 167m Er in order to characterize the structural properties of Er in Si [5][6][7][8][9]. While EXAFS investigates the immediate neighbourhood of the Er atoms and TEM visualizes the crystalline quality on a nanoscale, emission channeling measures the position of the Er nucleus with respect to the lattice of a single crystal.…”