Static Microindentation and Displacement-Sensitive Indentation Tests on Undoped GaAs
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0904-BB05-08.1
Static Microindentation and Displacement-Sensitive Indentation Tests on Undoped GaAs
Shanling Wang1, Ming Zhang1, Jodie Bradby2 and Pirouz Pirouz1 1 Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106 2 Department of Electronic Materials Engineering, Research School of Physical Science and Engineering, The Australian National University, Canberra, ACT 0200, Australia
ABSTRACT Static microindentation as well as dynamic displacement-sensitive indentation (DSI) tests have been performed between RT and 450oC on the (001) surface of undoped GaAs. In the static tests, the 4-fold symmetry reduces to 2-fold symmetry in some studied range of temperatures. The temperature dependence of the indentation diagonal and the crack length has been measured and, from disappearance of indentation cracks, the indentation brittle-to-ductile transition (IBDT) temperature TIBDT has been estimated. It is found that the temperature at which a transition in the energy density in DSI tests occurs nearly coincides with TIBDT as measured by static indentation tests; for undoped GaAs, both these temperatures are in the range of 200-225oC. This is about 100°C lower than the true brittle-to-ductile temperature TBDT, as measured by 4-point bending tests. The difference between TIBDT and TBDT is explained in terms of the superimposed hydrostatic stress component in the indentation experiments, and the crack asymmetry around the indentations is interpreted in terms of the different mobilities of α and β dislocations in GaAs. INTRODUCTION For investigating the plastic properties of semiconductors at low temperatures, indentation is a powerful technique because the complex stress field includes a hydrostatic component that suppresses fracture and allows the material to deform plastically rather than break into pieces. For this reason, numerous indentation studies have been carried out on a variety of semiconductors and indent characteristics such as indentation diagonal (proportional to hardness), rosette lengths, etc. have been measured as a function of deformation temperature, doping concentration, and surface and indenter orientation [1]. We have recently investigated the transition from brittle fracture to ductile plasticity in undoped GaAs using two different techniques, i.e. compression and bend tests [2]. As expected, the yield stress τy as measured by compression experiments varies exponentially with temperature; interestingly, a plot of ln(τy) vs 1/T exhibits two linear regimes with the slope abruptly changing at a critical temperature Tc, with Tc depending on the strain rate ε . This critical temperature Tc is found to approximately correspond to TBDT, as measured directly by 4-point
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bend experiments; both Tc and TBDT are in the range of 300-400oC for ε varying from 1x10-6 to 5x10-5 s-1 [2]. In this work, conventional static micro-indentation tests, as well as dynamic DSI tests, were carried out on the (001) face of undoped GaAs from room temperature, where
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