Blue monolithic AlInN-based vertical cavity surface emitting laser diode on free-standing GaN substrate

We report on III-nitride based blue vertical cavity surface emitting lasers using defect-free highly reflective AlInN/GaN distributed Bragg reflectors grown on c-plane free-standing GaN substrates. Lasing is demonstrated at room temperature under pulsed electrical injection. The high lasing threshold current density still prevents devices from continuous wave lasing because of large self-heating. The reasons for such a high threshold are discussed and we show that it mainly comes from large light absorption in the indium tin oxide current spreading layer. Properly tuning both its thickness and its position with respect to the electrical field could remarkably decrease the threshold.