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PACS 85.60.Jb This paper reports on the experimental methods of the determination of junction temperature and thermal resistance in GaN-based LEDs. For the direct temperature measurement and investigation of thermal distribution on the operating LED chip, nematic liquid crystal thermographic technique was employed. Hot spot was observed and its size was increasing with the driving input power. The initial hot spot with an anisotropic-isotropic transition of 29 o C appeared near the cathode region under the drive voltage of 2.95 V and the current of 8.1 mA. The size of the hot spot was increased with input power. Micro thermocouple was embedded into the epoxy package for the investigation of its size effects on thermal behavior. For the specific structure of LED package investigated the thermal resistances were calculated to be 265 o C/ W and 215 o C/ W for the low epoxy domed package and high epoxy domed package, respectively.

This paper reports on the thermal behavior of GaN-based laser diode (LD) package as functions of cooling systems, die attaching materials, and chip loading conditions. Thermal resistance and junction temperature was determined by electrical-thermal transient method. Significant change of thermal resistance with input current was observed under natural cooling condition due to the sensitive change of heat transfer coefficient (h) with temperature. Employment of PbSn as a die attachment was more advantageous over Ag-paste in thermal behavior of LD package. Compare the thermal resistance of LD packages epidown and epi-up structures. The partial thermal resistance from junction to submount is 4.68 K/W for epidown structure, and 9.65 K/W to epi-up structure. The results demonstrate that the total thermal resistance of LD package be controlled mainly by the packaging design rather than the chip structure itself.1 Introduction GaN-based blue laser diode (LD) is of significant importance for the applications such as optical data storage and communication system. It is well documented that the performances of LD products can be improved with higher laser power [1, 2]. However, high power operation leads to high junction temperature. High junction temperature degrades the optical performance, thus causes potential device failure and reliability problem [3,4]. Therefore, accurate and reliable characterization of thermal behavior is very important for the development of LD packages with a long-life time. The thermal resistance in the most useful indicator of thermal performance of LD package. The thermal resistance is defined as the ratio between the temperature difference between the junction and the ambient and dissipated power [5]. The thermal resistance is a direct indicator how much heat is generated under certain input power in the p-n junction, and it becomes a prime interest to package designers of high power GaN-based LD.In this paper thermal analysis was performed for different cooling system and structures of GaN LD packages. Thermal transient technique was employed for the investigation of thermal behavior. Thermal resistance was measured under forced cooling system and natural cooling system for samples with epi-up and epi-down structures. Thermal analysis was performed as a function of submount materials as well. The thermal resistance represents the contribution from each different layers of heat transfer path in LD structure. By this way, we investigated the thermal behavior as functions of input current and package structure of GaN-based LD package.

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PACS 02.70. Dh, 85.60.Bt, 85.60.Jb This paper reports on the thermal modelling of GaN-based LEDs. The theoretical calculation was made by combining an analytical simulation employing the Unit Temperature Profile Approach (UTPA) and Finite Element Method (FEM). An interfacing process was made by the optimization of the modelling input parameters used in the analytical simulator. The calculated temperatures of the LED chip inside the epoxy package was compared with the experimentally measured data and the optimized heat transfer coefficients were extracted. The extracted parameters were implemented into the numerical thermal calculation of the package surface using FEM. By the effective interfacing process between the two modelling tools, it is demonstrated that the analytical simulator can be utilized for the accurate prediction of the surface temperatures of LED packaging with non-flat surface.