Optoelectronic properties of (001) and (111) lattice-matched and strained quantum wire lasers--comparison with quantum well lasers

Abstract

We investigate the optoelectronic properties of GaAs wires along the [001] and [111] directions for a range of cross sections and compare these with the corresponding parameters for optimized quantum wells. The relative benefits of built-in strain in quantum wire and quantum well systems are also studied. We find that the threshold current density in the 100 x 50 A wire is 80 A/cm2 compared with 560 A/cm2 in a 50 A GaAs well. The differential gain in quantum wires is increased by an order of magnitude in comparison with quantum wells, and can be as high as 10-13 cm2. A narrow gain spectrum is calculated for quantum wire lasers ensuring high mode selectivity and strong damping of relaxation oscillations. We also consider the issue of carrier relaxation in quantum-confined structures, which may impose an upper limit on the laser modulation frequency. Performing a Monte Carlo simulation of the relaxation process, we find that the electron relaxation time in quantum wires is increased to above 100 ps in comparison with [approximate] 10 ps in quantum wells. Within our model, this unusually slow relaxation process may limit the small-signal modulation frequency of quantum wires to several GHz. Since modulation frequencies of over 30 GHz have been achieved in quantum wells, we conclude that although quantum wires posses superior optoelectronic properties as compared with quantum wells, the degraded small-signal response can make use of quantum wire lasers for high speed applications undesirable.