A study of the dislocations in Si-doped GaAs comparing diluted Sirtl light etching, electron-beam-induced current, and m
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A study of the dislocations in Si-doped GaAs comparing diluted Sirtl light etching, electron-beam-induced current, and micro-Raman techniques P. Mart´ın and J. Jim´eneza) F´ısica de la Materia Condensada, ETS Ingenieros Industriales, 47011 Valladolid, Spain
C. Frigeri CNR-MASPEC Institute, Via Chiavari 18/A, 43100 Parma, Italy
L. F. Sanz F´ısica de la Materia Condensada, ETS Ingenieros Industriales, 47011 Valladolid, Spain
J. L. Weyher High Pressure Research Center, Polish Academy of Sciences, U. Sokolowska 29/37, 01-142 Warszawa, Poland (Received 14 May 1998; accepted 19 January 1999)
Impurity atmospheres around dislocations have been studied in n-type Si-doped liquid encapsulated Czochralski (LEC) GaAs substrates by micro-Raman spectroscopy, diluted Sirtl-like etching with light (DSL) method, and electron-beam-induced current (EBIC). A complete morphological study of the recombinative atmospheres revealed by photoetching was achieved by phase stepping microscopy (PSM), which is an optical interferometry technique allowing to obtain the surface topography with a high vertical resolution (in the nanometer range). The minority carrier diffusion length was measured by EBIC at different points of the atmospheres. Structural distortion at the regions surrounding the dislocation core were observed by micro-Raman spectroscopy. The carrier depletion depth and the recombination of the photogenerated carriers were also studied by Raman spectroscopy, obtaining a good agreement with the EBIC data and the photoetching rates. Impurity gettering and diffusion and defect reactions involving As interstitials are assumed to play a major role in the formation of the recombinative atmospheres.
I. INTRODUCTION
Bulk GaAs plays a major role as a substrate for optoelectronics and microelectronics. The point defect concentrations and the electrical properties of asgrown ingots exhibit macroscopic and microscopic inhomogeneities. The interaction between dislocations and impurity and native defects produces strong local inhomogeneities, which negatively affect the electrical and optical parameters of the devices based on these substrates1,2 ; e.g., dislocations and microprecipitates reduce the quantum yield of the optoelectronic devices.3 To understand the factors causing the spatial variation of the electrical properties, knowledge of the mechanisms giving rise to the atmospheres decorating the dislocations is needed. Assessment of these inhomogeneities is essential to the improvement of the quality of the substrates. The main cause of the relatively high density of dislocations in liquid encapsulated Czochralski (LEC) a)
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J. Mater. Res., Vol. 14, No. 5, May 1999
crystals is its plastic deformation in the presence of thermal stresses during the post growth cooling. Semiquantitative information about the Cottrell atmospheres in GaAs can be obtained by chemical photoetching with DSL (diluted Sirtl-like etchant used
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