Polarity-induced changes in the nanoindentation response of GaAs
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Patriarche and L. Largeau Laboratoire de Photonique et de Nanostructures, UPR 20 CNRS, 91460 Marcoussis, France
J.P. Rivie`re Laboratoire de Physique des Solides et de Cristallogénèse, UMR 8635 CNRS, 92195 Meudon Cedex, France (Received 4 June 2003; accepted 22 September 2003)
We studied the polarity-induced changes in the nanoindentation response of GaAs{111}. The nanoindentations were made under a large range of loads (Fmax between 0.2 mN and 50 mN) at room temperature on {111} faces of A (Ga) or B (As) character. The loading–unloading curves were compared first, with special attention addressed to pop-in events and hardness values (reported previously for microindentation). Transmission electron microscopy was used to observe the nanoindentation structures generated at the two polar surfaces. The size of the dense plastic zone generated around the indent site was found to increase linearly with √Fmax and similarly for both polar surfaces. The indentation rosettes possess a threefold symmetry with arms developed along the directions parallel to the surface. Sizes were found to be very close for both polar surfaces and the entire load range. For an A-polar face, the rosette arms are constituted by two arms: a long arm (LA, ␣ dislocations) and a short arm ( dislocations). At the B surface, only the LA ( dislocations) are formed. Furthermore, microtwinning was observed only for an A-polar face, similar to previous observations of anisotropic microtwinning at GaAs(001) surfaces.
I. INTRODUCTION
The thermomechanical properties of semiconductors such as GaAs are very important to optoelectronic applications as they determine the structural quality of the heterostructures and therefore the performance of the devices. When misfit structures are required, the performance is dramatically affected by threading dislocations that extend through the active layers. The mechanisms by which such dislocations appear in mismatch structures are still controversial. Recently, by modifying the surface of the substrate (compliant substrates in the 001 orientation), the structural quality of heteroepitaxial layers can be improved.1,2 The nanoindentation technique has proved to be of great importance in this field of research, as it allows investigation of the plastic response of surfaces and thin
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 19, No. 1, Jan 2004
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films. Indeed, the probe size can be controlled by adjusting the load applied to the indenter, and very low load ranges have become available so that formation of cracks during the tests can be avoided. Previous studies reported differences in the mechanical response of {111} GaAs according to the polar character.3 In particular, in the microindentation domain, the hardness was shown to be dependent on the polar character of the surface (A or B). Moreover, the type of doping (n or p) played an important role in the response. Indeed, for the n type, the A f
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