Chaudhuri This award provides partial support for instrumentation for the high resolution x-ray characterization of defects and strain in group III nitride based wide band gap semiconductors. A high resolution triple axis materials research diffractometer capable of measuring x-ray rocking curves as well as reciprocal space maps will be acquired. In this unit a triple axis adding a triple-bounce channel-cut Ge(220) analyzer crystal turns the double axis diffractometer into a triple axis diffractometer which gives it a high resolution. Using this diffractometer the interplanar spacing variation due to the strain can be separated from the tilt caused by defects like dislocations. Thus the diffraction peak of a thin film even with a large number of dislocations would be sharp at a certain scanning mode (w - 20 scanning mode) and the peak position can be measured accurately. This will give more precise information on lattice parameters, structure and strain of materials than a double crystal diffractometer. In addition one can obtain the reciprocal space map of the substrate and film separately which gives information on the strain and defects simultaneously. These findings with a high resolution are essential in developing new smaller dimension wide band gap semiconducting materials with less defects and strain and improved opto-electronic properties. The material systems to be studied are used in optical and electronic devices. The structure, strain, composition, defects and polarity in these materials will be analyzed using a comprehensive x-ray diffraction technique which consists of the x-ray high resolution diffractometry and x-ray topographic techniques. These parameters are important because optoelectronic properties and device performance are strongly dependent on them. The experimental values will be compared with the theoretical ones and models will be developed to explain the strain and defects. Specific recommendations will be given to the crystal growers based on these models and improved device fabrication will be realized. Thus a significant contribution can be made in the field of nitride based wide band gap semiconductor devices. This research will be done in collaboration with Kansas State University, Manhattan, KS and other places.
This diffractometer will also be made available to other researchers at Wichita State University and at other universities in the state of Kansas. At present there are no high resolution triple axis diffractometers in the state of Kansas. Materials research has been identified as one of the strategic techniques in the state of Kansas. The materials research diffractometer requested is versatile and can be used for many other applications by other researchers in Wichita State University and other universities in Kansas. The research capabilities of other researchers in Kansas will be improved profoundly with this equipment. In addition, students will be trained in the use of x-ray diffraction technique and will be involved in research by using this equipment both at the graduate and undergraduate levels. %%% ***
