Mohammad Sadegh Nazari

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Direct measurements are reported of self-heating in an AlGaN/GaN transistor using ultraviolet and visible micro-Raman. Device stack is comprised of silicon substrate, AlN nucleation, AlGaN transition, GaN buffer, and AlGaN barrier layers. Phonon shifts are used to estimate temperature rise. Ultraviolet measurements probe the current- carrying GaN near the(More)
A method is described for directly measuring the temperature of a substrate in a molecular-beam epitaxy (MBE) growth system. The approach relies on the establishment of the temperature dependence of Raman-active phonons of the substrate material using independently known calibration points across the range of interest. An unknown temperature in this range(More)
OBJECTIVE Accurate delivery of torque to implant screws is critical to generate ideal preload in the screw joint and to offer protection against screw loosening. Mechanical torque-limiting devices (MTLDs) are available for this reason. In this study, the accuracy of one type of friction-style and two types of spring-style MTLDs at baseline, following(More)
Visible and ultraviolet (UV) micro-Raman spectroscopies are used to study the stress in GaN integrated with diamond grown by chemical vapor deposition. Mapping of stress is accomplished across a 75-mm GaN-on-diamond wafer. UV measurements from both sides of the wafer reveal an unexpected gradient between the tensile stress from the free GaN surface (~0.86(More)
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