Optical Studies of The Uniformity of Thermally Induced In-Plane Strain in Thin Gallium Arsenide Films

Abstract

In-plane anisotropic strain can be employed in the design of a new class of optoelectronic devices, such as high contrast, polarization sensitive spatial light modulators. One of the key issues involved in realizing these devices is obtaining a controllable and uniform in-plane strain. We have studied the uniformity of thermally induced in-plane strain in MOCVD grown GaAs lift-off thin films mounted on LiTaO₃ or CaCO₃ substrates. The experiment exploits the straininduced splitting of the excitonic interband transition at low temperature through absorption measurements using a Ti-Sapphire laser focused to a spot size less than 100 μm. The polarization vector of the incident light was oriented along an axis which enhances both features. From the energy positions of these transitions, the magnitude as well as the type of the in-plane strain was determined. Topographic scans performed over a 1.4mm X 1.4mm area for the sample bonded to CaCO₃, and along a 2 mm line for that bonded to LiTaO₃ revealed variations in strain of less than 5%.