Solid-solution strengthening in ordered In_xGa_1 − xP alloys

Abstract

Ordered In x Ga 1 À x P alloys have been grown on to GaAs(001) substrates by metal-organic vapour-phase epitaxy. Lattice-matched compositions of alloys (In x Ga 1 À x P with x % 0.5) were used in order to produce epitaxial layers free of structural defects (threading dislocations). Growth temperature and substrate orientation were adjusted to control the degree , of order, of the alloys in the range 0.3-0.5. Nanoindentation tests were carried out to measure the mechanical response of the heteroepitaxial layers. Transmission electron microscopy was used to characterize the structure as well as the plastic zones generated into the specimen by nanoindentation. Comparison of the alloys with binary references (InP and GaP bare substrates) showed strengthening, with the hardness and flowstress values that are much larger than those of InP and of the same order of magnitude as those of GaP. } 1. Introduction Solid-solution strengthening of III-V semiconductors has been used to reduce the density of dislocations introduced during their growth and to improve their mechanical behaviour (Ehrenreich and Hirth 1985, Rabier andGeorge 1987). The mechanical properties of semiconductors are relevant in connection with optoelectronic applications. The development of heterostructures has shown that the performance of devices is dramatically affected by threading dislocations that extend through the active layers. However, the mechanisms by which such dislocations appear in mismatched structures is still controversial. Recently, by modifying the surface of the substrate (compliant substrates), the structural quality of heteroepitaxial layers has been improved (Patriarche et al. 2000a,b, Patriarche andLe Bourhis 2000). Further improvement in the structure and performance of the devices is expected once the strengthening of the different layers has been engineered.

Cross-sectional transmission electron microscopy observations on the Berkovich indentation-induced deformation microstructures in GaN thin films

“…In the past, much effort has been devoted to characterizing the optical, electrical and magnetic properties of the resultant structures and devices. Recently, it has become clear that, in order to fully harvest the unprecedented 6 Author to whom any correspondence should be addressed. potential of the emerging nanotechnologies in general, the processes-induced structural and mechanical modifications on the materials might be equally important.…”

“…In this respect, the advent of nanoindentation instruments and the subsequent development of the underlying science may potentially address the scaling issue and the scientific evaluation of all contact loading related phenomena. Since the deformation that occurred during the test is controlled locally on the nanometre scale, nanoindentation has, recently, been widely used to investigate the deformation mechanisms of various semiconductors [4][5][6], in combination with the molecular dynamics simulations for analysing the atomic interactions [7][8][9]. In addition, the mechanical properties of surfaces of solids and thin films, such as the hardness and Young's modulus, have been extracted using this technique [10][11][12].…”

“…Therefore, complementary methods capable of providing such information are needed. In most nanoindentation studies, both Raman microspectroscopy [5] and planview TEM [6] techniques have been successfully used to analyse the phase transformation and defect/dislocations propagation along the horizontal direction of materials. However, they are inadequate to distinguish the phase changes inside the deformed zone along the direction of the concentrated applied stress.…”

Elastic Properties

“…It can be seen from Figures 3.17 and 3.18 that the microhardness is almost linear with respect to x, except in the case of Ga x In 1Àx P. The considerable strengthening observed in Ga x In 1Àx P (x $ 0.5) was attributed to the high crystal friction as confirmed by the flow-stress values [20].…”

“…20 Microhardness H versus x for Be x Zn 1Àx Se at 300 K. The experimental data are taken from Waag et al…”