We investigated characteristics of high performance GaN‐based laser diodes grown on LEO‐GaN/sapphire and free‐standing GaN substrates. The maximum output power was 300 mW under cw operation. The operation current and voltage were 53 mA and 4.67 V, respectively, for 30 mW‐output power. Thermal simulation and junction temperature measurement of laser diodes showed that epi‐down bonding was essential for the use of sapphire substrate. It was proposed that Mg diffusion into active layers was responsible for the degradation mechanism of GaN‐based laser diodes. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Improvements of external quantum efficiency of InGaN-based blue light-emitting diodes at high current density using GaN substrates

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AlGaN ∕ GaN multiquantum barriers (MQBs) were introduced into violet AlInGaN laser diodes with an InGaN multiquantum-well structure, resulting in drastic improvements in lasing performance. Comparing with conventional AlGaN single electron blocking layer (EBL), lower threshold current of 32mA and higher slope efficiency of 1.12W∕A at room temperature has been achieved by using the AlGaN∕GaN multiquantum barrier. This improvement implies that p-type AlGaN∕GaN MQBs are more effective in suppressing the overflow of electrons than p-type AlGaN single EBL. Effective barrier heights of the MQBs should be higher than the single EBL due to the quantum effect of MQBs and the enhancement of p-type doping efficiency. Additionally, the effect of strain on InGaN multiquantum wells from the single EBL can be reduced by using the AlGaN∕GaN MQBs structure.