Reduced threshold current density due to excitonic optical gain in the presence of dislocations and surface states in tensile strained ZnCdSe quantum wire lasers

Higher binding energies (30–60 meV) in II–VI wide-gap materials result in large exciton densities, making optical transitions due to excitons dominant over free electrons and holes. Optical gain and threshold current densities in ZnCdSe based multiple quantum wire lasers are computed including the effect of strain. It is found that the tensile-strained quantum wires yield lower threshold current densities than compressive strained or unstrained structures. The calculated threshold current density for a defect free tensile-strained ZnCdSe–ZnMgSSe quantum wire laser, realized on an InP substrate, has been computed to be 58 A/cm2. The exciton transitions assist in lowering the threshold current density which is adversely affected by the presence of dislocations and surface states. It is found that the threshold current density would increase to 435 A/cm2 assuming 1017 cm−3 trapping levels due to dislocations and surface states. However, taking into account the exciton transitions, the threshold current density is reduced to 79 A/cm2 when assuming the same trapping level density.