Enhanced optical gain in InGaN–AlGaN quantum wire and quantum dot lasers due to excitonic transitions

This article presents computation of optical gain and threshold current density in InGaN–AlGaN quantum wire and dot lasers in the presence of dislocations and surface states. The exciton binding energy including the effect of strain induced piezoelectric field is calculated to be 10–80 meV in InGaN–AlGaN quantum wires and dots, depending on the lateral and transverse dimensions. In contrast to the conventional GaAs or InP based quantum wires, these high binding energy results in large exciton densities, making optical transitions due to excitons dominant over free electrons and holes. Optical gain and threshold current density in InGaN–AlGaN based multiple quantum wire and dot lasers are computed including the effect of dislocation-induced traps. The calculated threshold current density Jth for defect free compressive-strained InGaN quantum wire (50 Å×50 Å) and dot (50 Å × 50 Å × 50 Å) lasers, realized on sapphire or SiC substrates, are shown to yield ultralow threshold current density of 233 and 88 A/cm2, respectively. In the presence of dislocations (1×1010 cm−2), the threshold current densities only increase to 924 and 623 A/cm2 for the same wire and dot, when we include the contribution of excitonic transitions. However, the corresponding values increase significantly to 30 838 and 11 647 A/cm2 if the exciton enhancement is not included.