Blue high power InGaN semiconductor laser diodes: Design optimization of laser bars and single emitters for best performance and reliability

Abstract

Blue high-power semiconductor lasers have increased greatly in performance over the recent decade enabling new application fields from high brightness projection up to materials processing beyond 1000W output power systems. Base for best system performance is optimal chip design and reliability of the semiconductor device. In this paper chip design optimization of blue high-power semiconductor laser bars will be shown: In contrast to IR laser bars with high lateral emitter fill factors beyond 50%, optimum design with maximum output power and efficiency for GaN laser bars is currently at very low fill factors in the range of 10%. Laser bar designs ranging from 5% fill factor up to 12.5% fill factor were fabricated and investigated. Additionally, two different emitter pitches with 200μm and 400μm were compared. The design with an emitter width of 30μm and a pitch of 400μm resulted in overall best performance. Additionally, lifetime investigations of single emitters in TO-packages will be discussed. The laser diodes were tested up to 5000h duration at different conditions in operating temperatures ranging from 64°C to 96°C and output power up to 3.5W. Dominating degradation mechanism is wear-out which is accelerated by optical output power and additional thermal activation. Extrapolation of the test results in combination with an acceleration model points towards a median lifetime of up to 65.000h for 25°C operation.