Measurement of junction temperature in GaN-based laser diodes using voltage-temperature characteristics

With increasing demands for the development of high power GaN-based blue-violet laser diodes (LDs), thermal management has become an important issue. We present a new method to determine junction temperature of GaN-based LDs for simple, fast, and reliable characterization of thermal performances. The large change of forward operation voltage with temperature is advantageously used to measure junction temperature. Using this method, we compare junction temperature of LD structures with different substrates and chip mounting methods. It is found that the junction temperature can be reduced considerably by employing GaN substrates or epi-down bonding. For epi-down bonded LDs, as much as two-fold reduction in junction temperature is achieved compared to epi-up bonded ones and temperature increase in this case is only about 13 degrees for more than 100 mW-output power.