9701657 Yodh The proposed work seeks to employ second-order nonlinear optical techniques to study buried solid interfaces. The nonlinear optical method is particularly attractive because it possesses the long penetration depths characteristic of most optical probes, and the intrinsic interface sensitivity characteristic of all second-order optical processes. The research will vigorously apply our nonlinear tools to new classes of scientifically interesting solid-solid interface systems including hererofilm structures such as SiC/Si and SiC/SiO2, metal/GaAs,metal/ZnSe,ZnSe/GaAs, II-VI-based Quaternary thin films on InP,and III-N nitride-based thin film structures. Loosely speaking, high quality films of these materials are required for the next generation of electro-optic devices such as blue light emitters and photodetectros. The proposed investigations will encompass a range of open ended polarization and frequency-dependent investigations. The polarization studies have the potential to identify gross structural problems associated with the growth of these thin films such as mixed phases, and misorientation. The frequency-dependent studies of the solid interfaces, and in many cases of the bulk thin films as well, will provide unique spectroscopic information about these systems with the potential to reveal new information about defects, band profiles, and strain in these systems. %%% When dissimilar crystals are abruptly adjoined, an interfacial region is formed with physical properties that are fundamentally different from those of the neighboring bulk materials. Since the microscopic characteristics of the junction often play a prominent role in determining the macroscopic properties of the material, the junction is important to understand. At the most basic level we would like to understand how specific interfacial stoichiometries bring about particular interfacial energy level structures, band offsets, band profiles, and morphologies. On a mo re technological level, "interface quality" is known to affect the properties of injection lasers and LED's, as well as charge transport in photodetectors and microelectronic circuits. A roblem of great fundamental and practical importance then, is to elucidate the role played by various interfacial properties such as level structure in affecting the properties of the material as a whole. Unfortunately the buried solid interface is difficult to probe by conventional means because traditional optical spectroscopies lack interface specificity, and traditional surface diagnostics have a limited penetration depth. The proposed work seeks to employ second-order nonlinear optical techniques to study these interfaces. The nonlinear optical method is particularly attractive because it possesses the long penetration depths characteristic of most optical probes, and the intrinsic interface sensitivity characteristic of all second-order optical processes. ***
