STUDY OF MBE GROWN ALINGAAS/ALGAAS QUANTUM WELLS AND THEIR APPLICATION IN SEMICONDUCTOR LASERS

Abstract

In this thesis strained AlInGaAs/ AlGaAs quantum wells grown by MBE are investigated. The AlInGaAs/ AlGaAs quantum wells are also incorporated into GRINS CH structure quantum well lasers, and the performance of the lasers is studied. The emission wavelength of the AlInGaAs/ AlGaAs quantum wells is very sensitive to growth temperatures. The sensitivity is due to In desorption during the MBE growth. At 600 °C growth temperature, In sticking coefficient is deduced to be about 0.54. AlInGaAs/AlGaAs quantum wells grown at high temperatures show good photoluminescence. Though the composition uniformity of the wafers grown at high temperatures is not as good as these grown at lower temperatures, high growth temperatures are still preferred for the opto-electronic application of the quantum wells. The flux ratio of group V element to that of group III elements must be more than about 10 to ensure good crystalline quality. Matthews and Blakeslee's criterion for critical thickness is found to be suitable as applied to the strained AlInGaAs/AlGaAs quantum wells. Wavelength tailoring of the AlInGaAs/AlGaAs quantum wells is performed, and the beam equivalent pressures required for obtaining 810 nm emission wavelength are found. The 810 nm lasers are of considerable interest since they are used as pump source for Nd:YAG solid state lasers. Stripe lasers processed from the GRINSCH AIInGaAs/ AlGaAs quantum well laser wafers show good I - V and L - I characteristics. The spectrum of the lasers shows multiple longitudinal modes. Lasers processed from wafers grown at high temperatures have lower threshold current densities than those from wafers grown at lower temperatures. It is found that some of the lasers emit at two distinct wavelength regions. With the increase of the injection current, the short wavelength appears first and then does the longer wavelength. For some of the lasers, the spectrum intensity of the shorter wavelength is always higher than that of the longer wavelength, but for some of the other lasers the intensity of the longer wavelength will surpass that of the shorter wavelength when the injection current is high enough. Investigations are being carried out on this phenomenon, however the work is outside of the scope of the thesis and is not presented.