Engineering Research Grant: X-ray Diffractometer

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We are requesting funding for the purchase of an X-ray diffractometer for our compound semiconductor materials and devices research. We chose a compact bench top model which is specifically designed for the characterization of compound semiconductors. This diffractometer will allow us to make precise measurements of the lattice constants of grown epitaxial layers on binary alloy substrates and assess the quality of the epi-layers. Many of the on-going research programs will benefit from the acquisition of the X-ray diffractometer. Our experimental studies on strained-layers and hetero-epitaxy have mainly relied on optical and electrical characterization techniques. In order to pursue a thorough investigation more attention must be paid to the structural properties of the materials. For a number of the device research programs, it is necessary to grow perfectly lattice-matched hetero-junctions for some specific applications. The X-ray diffractometer will provide us with information on the exact amount of mismatch so that very fine adjustments can be made in the growth parameters to obtain lattice matching. Accurate measure of the mismatch is also required for the study of different strain effects in various III-V material systems. Furthermore, knowledge of the alloy compositions in the heterostructures is important in optimization of the devices and correlation of the device performance to the structural parameters. X-ray diffraction measurement is the most direct means of determining the alloy compositions in layered structures. We have developed organometallic chemical vapor deposition techniques to grown high quality III-V structures for our material and device research programs. Addition of a double-crystal X-ray diffractometer will undoubtedly enhance these programs and provide crucial steps for further advancement.