Optically Detected Magnetic Resonance of Arsenic Antisites in GaAs MBE Layers Grown at Low Temperatures
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Optically Detected Magnetic Resonance of Arsenic Antisites in GaAs MBE Layers Grown at Low Temperatures F. C. Rong,1',a) L. Fotiadis,1',) H.-J. Sun,2 G. D. Watkins, 2 M. A. Taysing-Lara,1 J. Flemish,' and W. H. Chang1 'Electronics Technology and Devices Laboratory, Fort Monmouth, NJ 07703 2 Sherman Fairchild Laboratory, Lehigh University, Bethlehem, PA 18015 ABSTRACT Observation of Arsenic antisites (AsGa) in GaAs layers grown by molecular beam epitaxy (MBE) at low substrate temperatures (- 200'C) is reported, using electron paramagnetic resonance (EPR), magnetic circular dichroism in absorption (MCDA), and MCDA tagged by optically detected magnetic resonance (MCDA-ODMR). This experiment confirms that there is a MCD absorption band directly associated with AsG, in the GaAs layers. The AsGa concentration in the GaAs layers is found to decrease by about one order of magnitude after annealing at 600 C for two minutes. INTRODUCTION Thin epitaxial GaAs layers grown by molecular beam epitaxy (MBE) at unusually low temperatures (LT) between 200 - 300 'C, as opposed to the regular growth temperatures of 550 - 600 * C for GaAs, are of current interest in view of their technological importance as insulating buffer layers in GaAs devices and integrated circuits, 1 ,2 as well3 as many unusual physical properties such as the recently-reported superconductivity. Despite the low growth temperatures, LT GaAs layers remain crystalline up to a limited epitaxial thickness.4 A high concentration of compensating deep-level defects is introduced during growth, being responsible for the desirable high resistivity of the material. Using electron paramagnetic resonance (EPR), the dominating point defects of the material have been identified as arsenic antisites (AsGa, an arsenic atom occupies a gallium site) with concentration as high as - 1019 cm- 3 in as-grown layers.' In this paper, we would like to report the first direct optical detection of AsGa in such layers using magnetic circular dichroism in absorption (MCDA) and MCDA tagged by optically detected magnetic resonance (MCDA-ODMR)6 . MCDA-ODMR is a well-established technique to probe chemical signatures of 7 AsGa in GaAs bulk materials, such as the well-known EL2 center. Not only is the sensitivity of the technique often higher than that of conventional EPR, but also it links the EPR signature of a paramagnetic defect under investigation with the MCD of an absorption band associated with that defect. EXPERIMENTAL CONDITIONS The measurements were done on 3-p m MBE-grown LT GaAs single layer on (100) semi-insulating GaAs substrates. The layer was grown around 200 °C in the MBE machine of US Army ETD Laboratory, and it was not annealed above the growth temperature in the machine. For a preliminary annealing study, a standard rapid thermal annealer was used to anneal samples at 600 0 C for 30 seconds or 120 seconds. The asMat. Res. Soc. Symp. Proc. Vol. 241. ©1992 Materials Research Society
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grown layer quality was reasonable, as shown in Fig. 1 by double-crystal x-ray diffraction
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