High Resolution Transmission Electron Microscopy Study of Se + Implanted and Annealed GaAs
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HIGH RESOLUTION TRANSMISSION ELiECTRON MICROSCOPY STUDY OF Se+ IMPLANTED AND ANNEALED GaAs D.K. SADANA*, T. SANDS AND J. WASHBURN Materials and Molecular Research Divisions, Lawrence Berkeley Laboratory, University of California, Berkeley, CA 94720;*Now at Microelectronics Center of North Carolina, Research Triangle Park, NC 27709. ABSTRACT High resolution transmission electron microscopy (HRTEM) has been ap~lied to the study of amorphization and recrystalli tionnmechanisms in Se implanted (100) o GaAs. An Se dose of 1 x 10 cm at 450 keV (projected range 1550A) produced an amorphous band in the depth range 250 to 2150A below the surface. Annealing at 400 0 C resulted in ;he epitaxial regr&wth of the upper and lower transition region (0-250A and 2150 2500A, respectively). Regrowth of the amorphous layer was found to proceed by the nucleation and propagation of the dense network of stacking faults bundles. These bundles disappeared on higher LŽ600 0C) temperatur$ annealing. Amorphization and recrystallization mechanisms in Se implanted GaAs are discussed in light of these HRTE7 results. INTRODUCTION Conventional (bright-field and weak-beam) transmission electron microscopy (TEM) and Rutherford backscattering (RBS)/ channeling have been utilized extensively for _rjytural examination of ion implanted and subsequently annealed GaAs. It is known from these measurements that amorphous layers producedlbp7ion implantation recrystallize at a much 0 lower temperature (150-200 C) than analogous amorphous layers of Si 0 (450 C). Another important difference in the recrystallization behavior of these two materials is that regrowth of amorphous layers in (100) Si can result in essentially defect-free material, whereas regrowth of amorphous GaAs layers in (100) GaAs usually results in microtwins,ogtfc, faults, misoriented crystallites and other irregular structures . These differences are also reflected in the electrical behavior of recrystallized layers. For example, the optimum electrical activation (90-100%) of dopants in Si is achieved when the implanted region is completely amorphized before annealing. However, if4 GWAs such conditions result in the lowest activation of dopants (~10%) . Better electrical results in GaAs have been reported for elevated temperature (>100 0 C) fwlants for which amorphization of the implanted region does not occur . It is therefore apparent that more detailed characterization of amorphized and regrown GaAs is necessary. In this communication, the high resolution TEK (HRTER) and conventional TE4 results from Se implanted and furnace annealed GaAs are presented along with a phenomonological discussion of GaAs amorphization and recrystallization mechanisms. EXPERIMENTAL Selenium ions accelerated to 450 keV were implanted at nominal room tejuera~ure into semi-insulating Cr-doped (100) GaAs samples to a dose of 10 cm-. The implanted samples were capped with Al and then annealed in a furnace in the temperature range 400-800 0 C. For TE7A analysis, specimens of both plan and cross-sectional geometries w
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