Recent advances in c-plane GaN visible lasers

Abstract

Blue and green InGaN-based R&D laser structures on c-plane GaN substrates are investigated. We analyzed carrier injection efficiencies as well as internal quantum efficiencies up to laser threshold. The injection efficiency of the blue laser structure is measured to be 78%. The internal quantum efficiency of spontaneous emission reaches 50% at 30A/cm2 and 32% at laser threshold. For the green laser structure we found an injection efficiency of 71%, a maximum of internal efficiency of 36% and, at laser threshold. a value of 28%. Both, recombination on defects as well as Auger effect are identified as relevant loss processes up to the laser threshold. An improved 515nm R&D single mode laser in TO56 can is presented. The optical output power of the green single mode laser reaches 250mW in continuous wave operation underneath thermal roll-over. Wall plug efficiency is as high as 9%. In the next step we investigate high power multimode lasers. The new power green R&D laser reaches maximum power of 1.25W at thermal roll-over. The currentoutput characteristic is nearly linear up to 0.9A and 0.6W. At higher currents thermal bending is observed. We measured a maximum wall plug efficiency of the green multimode laser of 13%. The power blue R&D laser in TO90 metal can reaches 5.5W prior to roll-over having the wall plug efficiency of 32% at 3.5W.