Improvement of hole injection and electron overflow by a tapered AlGaN electron blocking layer in InGaN-based blue laser diodes

Abstract

We studied the influence of a tapered AlGaN electron blocking layer (EBL) with step-graded aluminum composition on hole injection and electron overflow effects in InGaN-based laser diodes (LDs) theoretically. Schrödinger-Poisson self-consistent method together with transfer matrix method was applied to calculate carrier distribution and transport properties for both electrons and holes in tapered EBL and conventional EBL. The results indicate that the new structure favors the tunneling of low energy holes from the p-side to the active region. Meanwhile, more uniform carrier distribution and better balance between electrons and holes are obtained for the tapered structure by proper modification of band diagrams. An advanced device simulation shows the elimination of electron overflow even at a current of 180 mA in the LD with tapered EBL. Decrease of threshold current density from 2.0 kA/cm2 to 1.6 kA/cm2 is benefited from the more uniform local gain profile.