Buried Amorphous Layer in Gallium Arsenide
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BURIED AMORPHOUS LAYER IN GALLIUM ARSENIDE D. Sengupta, M.C. Ridgway, J.M. Zemanski and S.T. Johnson Microelectronics and Materials Technology Centre, Royal Melbourne Institute of Technology, Melbourne, Victoria, Australia INTRODUCTION Relatively low dose oxygen implant is used for isolation and carrier removal in GaAs. Ion implantation induced damage is a function of ion mass, ion dose, dose rate and substrate temperature. In this paper, we explore the production of such damage leading to amorphisation in single crystal GaAs due to Oxygen ion implantation. We have also studied the solid state regrowth behaviour of such amorphous layers. It has been previously observed that GaAs implanted with other ion species has a very complex regrowth process 1,2]. Unlike amorphous silicon, that exhibits a regrowth with a planar amorphous crystalline interface and defect free recrystallized region, lower temperature regrowth of GaAs (less than 600 0 C) is characterized by formation of heavily twinned regions and thickening of crystal amorphous interface and in the extreme cases loss of planarity at the crystal-amorphous interface [3]. We encounter some of these behaviours in our recrystalization studies. EXPERIMENTAL The substrates used were semi-insulation (100) GaAs. 0+ ions were implanted with energy in the range 100-150 keV. The dose was varied over the range 2 - 7.5 x 101 5/cm 2 and the substrate temperature was varied over the range 00 to 150 0 C. The dose rate was kept reasonably constant at "i/LA/cm 2 . The buildup of implantation-induced damage was monitored during implantation by the intensity of scattered laser light from the surface of the crystal (TRR). Typical spectrum is presented in fig. 1. In addition channelled Rutherford backscattering (C-RBS) and transmission electron microscopy was used to characterise the samples. The thermal regrowth Kinetics were studied over the temperature range 250 to 300 0 C using a standard TRR set up [4]. RESULTS AND DISCUSSIONS Figure 1 that summarises the effects of different inplant conditions on final damage level. The scattering intensity is minimum for an undamaged crystal (-1 in arbitrary units) and maximum for an amorphous layer (-33 A.U.). The figure shows that samples implanted at 0°C for doses greater than 2 x 10"5 /cm 2 forms an amorphous layer, the width of the layer increasing with dose. At 200C and dose of 3.5 x 1015/cm 2 it was possible to produce buried amorphous layer. The oscillation of TRR signal is a clear indication of the onset of amorphisation at a location where majority of the ions stop. At higher doses the amorphous region spread in both directions, eventually reaching the surface. For implants undertaken at higher sample temperature, it was not possible to produce any amorphous layer due to self annealing and one obtained damaged layer with higher scattered intensity than pure crystal, but less than the amorphous level. Mat. Res. Soc. Symp. Proc. Vol. 163. ©1990 Materials Research Society
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Figure 1 TRR trace for the damage buildup during
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