AlGaN/GaN based high electron mobility transistors (HEMTs) have been intensively used due to their high-efficiency power switching and large current handling capabilities. However, the high power densities and localized heating in these devices form small, high temperature regions called hotspots. Analysis of heat removal from hotspots and temperature control of the entire device is necessary for the reliable design of HEMT devices. For accurate analysis of heat transfer using thermal simulations in such devices with heat transfer occurring at different length scales, a roadmap is needed. For this purpose relative importance of different heat transfer modes in removing heat from devices with different substrate materials, operating at different power densities while different boundary conditions are analyzed using two and three-dimensional COMSOL Multiphysics simulations. Results give the relative importance of different parameters on the heat removal mechanism from devices and provide a roadmap for building simpler yet still accurate thermal models for AlGaN/GaN HEMTs and similar devices.

Solid state lighting devices with high power densities require accurate characterization, as the rise of chip temperature impacts its optical, electrical, and lifetime characteristics. A detailed experimental study is performed in order to analyze opto-electro-thermal behavior as new high-power devices like laser diodes are becoming of interest. The outline of this article was inspired by two major issues identified in previous experimental approaches. First, there is some debate in the literature about the linearity of the temperature coefficient of the forward voltage. Second, there is a limited number of experimental reports on the temperature dependence of power conversion efficiency. We have shown that prior variations are the result of a diversity in the selection of electrical parameters during thermal calibrations, as both linear and non-linear relationships for temperature coefficient of voltage can be obtained. On the other hand, it was discovered that report scarcity for temperature-dependent studies can be related to the use of passive approaches for temperature-dependent measurements. In temperature-controlled environments, short pulses with high current densities may not ensure the thermal equilibrium of the device under test due to small thermal capacitance. This issue, as well as the lengthy process of passive measurements can be addressed by implementing a dynamic measurement method presented in this study. Finally, linear power conversion efficiency trends with junction temperature are demonstrated for both blue LEDs and LDs at high current densities.

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In the new age of illumination, light emitting diodes (LEDs) have been proven to be the most efficient alternative to conventional light sources. Yet, in comparison to other lighting systems, LEDs operate at low temperatures while junction temperature (Tj) is is among the main factors dictating their lifespan, reliability, and performance. This indicates that accurate measurement of LED temperature is of great importance to better understand the thermal effects over a system and improve performance. Over the years, various Tj measurement techniques have been developed, and existing methods have been improved in many ways with technological and scientific advancements. Correspondingly, in order to address the governing phenomena, benefits, drawbacks, possibilities, and applications, a wide range of measurement techniques and systems are covered. This paper comprises a large number of published studies on junction temperature measurement approaches for LEDs, and a summary of the experimental parameters employed in the literature are given as a reference. In addition, some of the corrections noted in non-ideal thermal calibration processes are discussed and presented. Finally, a comparison between methods will provide the readers a better insight into the topic and direction for future research.

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