Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Thin film of GaAs/AlGaAs multiple quantum well (MQW) structure have been bonded to the lithium tantalate (LiTaO3) or calcium carbonate (CaCO3) substrates cut such that one of the linear thermal expansion coefficients almost matches that of the MQW while its orthogonal counterpart does not. By choosing the proper bonding and operating temperatures, in-plane anisotropic strain up to 0.3% has been achieved. The transmission spectrum shows an anisotropy in excitonic absorption which results in a polarization rotation of a light beam at normal incidence to the structure. The theoretical calculation is in agreement with the experimental results. Using the polarization rotation, we have demonstrated a novel MQW light modulator with an exceedingly high contrast ratio of 330:1.

The growth of ultra-thin oxide films by the thermal oxidation of silicon has been studied by low and medium energy ion scattering spectroscopies (LEIS and MEIS) and X-ray photoelectron spectroscopy (XPS). To help elucidate the diffusional and mechanistic aspects of oxide growth we have used sequential isotope oxidation (18O2 followed by 16O2). LEIS demonstrates that both 18O and 16O atoms are on the silicon surface under our growth conditions. MEIS also distinguishes 18O from 16O and gives a depth distribution for both with high accuracy. Our results show that several key aspects of the Deal-Grove model (oxygen diffusion to the Si-SiO2 interface and oxide formation at the interface) are consistent with our results for 50Å films. For very thin oxide films (15Å or less), we found a mixed isotopic distribution in the film, demonstrating more complex oxidation behavior.