Theoretical optimization of quantum wire array lasers for low threshold current density and high modulation frequency

Abstract

We show that as one decreases the cross-sectional area of quantum wire lasers, the threshold current decreases, but the carrier relaxation time increases. Since the electron relaxation time sets the upper limit on the modulation frequency, there is a tradeoff between speed and efficiency in quantum wire lasers. We derive the optimal wire cross-sectional area for a one-dimensional array of quantum wire lasers based on a balance between an acceptably high maximum modulation frequency and a desirably low threshold current density. We find that for a relaxation time of 60 ps, the quantum wire of 150×150 Å cross section has the lowest threshold current density of 560 A/cm2. If high-speed operation is not needed, the optimal choice for the quantum wire cross-sectional area is 100×50 Å with the threshold current density of 420 A/cm2. For optimized quantum wells with the same cavity losses, the threshold current density is ≊620 A/cm2. We also present the results for the threshold current density and the relaxation time that allow one to find the optimal quantum wire structure weighing the speed and efficiency considerations in accordance with their relative importance.