Optimization of Current Injection Area for Low-Threshold Operation of 3-D Lasers

We analyze the reduction of threshold current by optimizing the area of the active layer into which the carriers are injected. The optimal area is shown to depend on the size of the optical mode, cavity lifetime, and the optical properties of the active layer. We introduce a critical value for the cavity lifetime that depends only on the properties of the active layer and show how the optimal area can be estimated depending on the cavity lifetime with respect to its critical value. For optimization, two cases are considered, with and without optical absorption in the active layer outside of the injection area. The active layer is modeled as a double heterostructure with parameters relevant to nitride semiconductors and the optical mode is taken as for a micrometer-size cavity.