Ge Growth on Nanostructured Silicon Surfaces

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Ge Growth on Nanostructured Silicon Surfaces Ganesh Vanamu,1 Abhaya K. Datye,1 and Saleem H. Zaidi2 Department of Chemical and Nuclear Engineering & Center for Micro-Engineered Materials, University of New Mexico, Albuquerque, NM-87131 2 Gratings, Inc., 2700 B Broadbent Parkway, N.E, Albuquerque, NM 87107 1

ABSTRACT We report highest quality Ge epilayers on nanoscale patterned Si structures. 100% Ge films of 10 µm are deposited using chemical vapor deposition. The quality of Ge layers was examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution x-ray diffraction (HRXRD) measurements. The defect density was evaluated using etch pit density measurements. We have obtained lowest dislocation density (5×105 cm-2) Ge films on the nanopatterned Si structures. The full width half maximum peaks of the reciprocal space maps of Ge epilayers on the nanopatterned Si showed 93 arc sec. We were able to get rid of the crosshatch pattern on the Ge surface grown on the nanopatterned Si. We also showed that there is a significant improvement of the quality of the Ge epilayers in the nanopatterned Si compared to an unpatterned Si. We observed nearly three-order magnitude decrease in the dislocation density in the patterned compared to the unpatterned structures. The Ge epilayer in the patterned Si has a dislocation density of 5×105 cm-2 as compared to 6×108 cm-2 for unpatterned Si. INTRODUCTION High quality films of Ge on Si are of significant importance and can be used in high electron mobility devices [1], photodetectors in the range 1.3µm or 1.55µm for optical communications [2] and also for integrating III-V optoelectronic devices [3]. However, a 4% lattice mismatch and nearly 50% thermal mismatch between Ge and Si causes three major challenges for growing high quality Ge films on Si, (a) High surface roughness due to pronounced crosshatch pattern which creates difficulties in lithographic patterning [4], (b) High dislocation densities which are responsible for enhanced recombinations and decrease the efficiency of the Ge films and (c) High density of microcracks [5] and wafer bowing [6]. A common way of reducing lattice and thermal mismatches is to form a "virtual" substrate by growing a graded composition of the desired heteroepitaxial film on a defect-free Si substrate [7]. A constant composition layer of the desired lattice parameter can then be grown on this buffer layer. Graded SiGe films have been demonstrated with very low (2×106 cm-2) defect densities [8]. Recently, single relaxed Ge deposition on Si obtained superior quality epilayers compared to graded-multi relaxed SiGe buffer layers [9]. Mathews et al. first proposed that limiting the lateral dimensions of the sample prior to growth could reduce the dislocation density [10]. In this letter we show high quality Ge layers with dislocation density lower than 5×105 cm-2 on nanoscale patterned Si structures.

Mater. Res. Soc. Symp. Proc. Vol. 862 © 2005 Materials Research Society

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