Influence of barrier growth schemes on the structural properties and thresholds of InGaN quantum well laser diodes

Abstract

The influence of the (In)GaN quantum barrier growth temperature on the structural properties of the active region of blue–violet laser diodes has been investigated. Therefore, multiple quantum well structures were prepared by metal-organic vapor phase epitaxy, with (In)GaN barriers grown either at the same temperature as the InGaN quantum wells, or at a 60K higher growth temperature. A 60K higher growth temperature results in smoother quantum barrier layers with fewer defects on a microscopic scale, as revealed by scanning electron microscopy and cathodoluminescence studies. On the other hand samples with a 0K offset showed a higher strain in the quantum wells determined by X-ray diffraction and a narrower photoluminescence emission spectra. Secondly, laser heterostructures with InGaN barriers were prepared for optical pumping using different growth schemes. The laser structure with the active region deposited with a 0K offset exhibits significantly lower optical threshold power densities of around 200kW/cm² compared to 700kW/cm² for the 60K offset sample. Also, transmission electron microscopy revealed quantum wells with improved lateral uniformity in the samples grown without temperature offset. Based on these results, a current-injection broad area laser diode with an active region growth scheme without temperature offset was prepared on (0001) GaN substrate. The diode emits around 420nm with a threshold current density of around 1.6kA/cm².