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

The reduced and even negative temperature dependence of the lasing threshold current that has been observed around room temperature for some (Al, Ga)As double heterostructure lasers grown by molecular beam epitaxy (MBE) can be explained by a separation of the p-n junction from the active layer heterojunctions. This separation requires minority carrier diffusion into the active layer for lasing and also 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. First-order calculations of the temperature dependences of these effects are presented, showing good agreement with measured threshold current and junction voltage dependences. The separation of the p-n and heterojunctions in the lasers with a reduced temperature dependence is supported by secondary-ion mass spectroscopy, electron beam induced current, and photoluminescence results. Besides the negative temperature dependence of the threshold current for the anomalous devices, the same remote junction effect can explain variability in the threshold current temperature dependence of seemingly normal devices and wafer-to-wafer variability in room temperature threshold currents. An improved understanding of these effects can be important in the design of lasers and optoelectronic systems.