Abstract
We investigate loss mechanisms in 1.3mum lasers and in visible lasers operating between 630nm and 690nm by measuring the change in the threshold current with temperature from 77K to 350K and with hydrostatic pressure up to 15kbar. We compare the variation of threshold current density with temperature in visible lasers with theory and find that the major loss mechanism is carrier leakage to X-minima in the cladding. This conclusion is reinforced by a simple fit to data of threshold current density against hydrostatic pressure, in which the loss mechanism is seen as an activated rate of change of with pressure process with an activation energy roughly equal to the rate at which the X-minima and F-minimum are approaching each other with pressure. It is further concluded that this leakage is not a problem at room temperature at 670nm but causes the very high threshold current density and sensitivity to temperature seen in 635nm lasers. We combine pressure and spontaneous emission measurements, the latter carried out at several temperatures above room temperature, to deduce the cause of the high temperature sensitivity of 1.3mum lasers. From measurements of the pure spontaneous emission emitted from the side of the devices or from a window etched in the substrate, we conclude that the major loss mechanism and cause of the high temperature sensitivity in 1.3mum lasers is Auger recombination. Values deduced for the thermal activation energy associated with the Auger coefficient and the variation of the threshold current with pressure indicate it is a phonon-assisted Auger process. Such a process is only weakly dependent on band structure, which explains why the temperature sensitivity in these lasers was not improved by the introduction of strain.