Reduced threshold current temperature dependence in double heterostructure lasers due to separate p-n and heterojunctions

Pawlik et al. (1981) have observed a reduced temperature dependence of the lasing threshold current in some (Al, Ga)As double heterostructure lasers grown by molecular beam epitaxy (MBE). While lasers from most wafers exhibited the normal exponential temperature dependence, devices from a few wafers had a nearly constant or even decreasing threshold current temperature dependence near room temperature. It is proposed in the present investigation that the reduced temperature dependence of the MBE devices is due to a separation of the p-n junction by a small distance from the active heterojunctions. This separation requires minority carrier diffusion into the active layer for lasing and allows majority carrier current flow out of the active layer. The latter current does not contribute to lasing and adds to the current necessary to achieve lasing.