Strain dependence of threshold current in fixed-wavelength GaInP laser diodes

It has been reported that the threshold current of GaInP quantum-well lasers at a fixed wavelength of 633 nm as a function of strain has minima for both compressive and tensile strain. In these devices the well width is changed as the well composition is changed to maintain the fixed wavelength. We argue that the reported behavior can be explained simply in terms of the general behavior of the gain-current characteristics of 2-D structures as a function of well width, and a monotonic decrease in threshold current with increasing tensile and compressive strain. The minima arise from the strong effect of well width fluctuations in thin wells and the occupation of many sub-bands in wide wells. Other effects such as defect formation at high strain-thickness products may also play a part in the behavior of real devices, nevertheless we show that it is not necessary to invoke such an effect, nor gain saturation in thin wells, to explain the reported behavior. Our qualitative arguments are general, and have been verified by detailed calculations for 670 nm lasers