Gain guided laser diodes exhibit unexpected low threshold current densities. Under these conditions, lasing only occurs under a current dependent long-time delay, which is three orders of magnitude larger than the time needed to reach population inversion. This effect is attributed to a thermally induced index guiding. The change in temperature of the quantum well region can be estimated using the shift in the wavelength of emission to be up to 70 K. As a further consequence, the threshold current density can be reduced by a factor of 4 simply by changing the pulse width of the applied current.
Properties of excitons in quantum well structures of ZnCdSe/ZnSe and ZnSe/ZnMgSSe are compared. In ternary ZnCdSe quantum wells and at low temperature excitons are strongly localised. Weaker localization is observed in quantum well structures of ZnSe/ZnMgSSe. Present studies suggest formation of negatively charged excitons in the latter structures.
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