Different influence of InGaN lower waveguide layer on the performance of GaN-based violet and ultraviolet laser diodes

Abstract Two Series of InGaN/GaN quantum well laser diodes (LDs) with different InxGa1-xN lower waveguide (LWG) layers are investigated. For violet LDs with lasing wavelength of 405 nm, the threshold current and the output power are improved when the indium content of LWG increases from 0 to 6%. It is mainly attributed to the increase of optical confinement factor (OCF) and the decrease of the total optical loss (TOL) which are caused by the increasing difference of the refractive indices between InGaN and GaN (and AlGaN in cladding layer). However, for ultraviolet LDs lasing at 377nm, the InxGa1-xN LWG is not beneficial to the emission performance due to the decrease of OCF. Furthermore, when the indium content of LWG reaches a higher level, the performance of both violet and ultraviolet LDs will be weakened due to the obvious increase of carrier leakage current related to the enhancement of piezoelectric polarization effect.