Lasing phase diagram for semiconductor surface-emitting lasers

A new tool, a lasing phase diagram, for understanding semiconductor surface-emitting injection lasers has been synthesized. The diagram shows how to design laser resonators which have the lowest possible threshold currents and highest operating efficiencies. To create this diagram, the rate equations describing the photon and electron-hole densities in the laser are solved for the steady-state conditions. The solutions are compactly summarized on a single lasing phase diagram which shows the lasing threshold current and power efficiency contours as functions of two structural parameters (mirror loss and number of quantum wells) in a two-dimensional plane. The plane is separated into three regions corresponding to lasing, marginal lasing, and nonlasing structures. The diagram predicts that, in the high reflectance limit, the threshold current is independent of mirror loss and scales directly with the number of quantum wells in the active region. The phase diagram has been successfully used to understand the lasing characteristics of many different laser structures recently reported.