| The goal of this thesis is to demonstrate lateral carrier confinement in a vertical-cavity laser (VCL). In order to fully realize the benefits of carrier confinement, low-loss optical and current confinement are addressed. The optical waveguiding theory of dielectric-apertured VCLs, which is summarized, predicts that strong, low-loss optical confinement is possible using a dielectric with a tapered front. This structure is formed by lateral steam oxidation of the higher aluminum content layers in the VCL structure. Since it is desirable to tailor the characteristics of the taper such as its length and angle, a study of the properties of AlGaAs-oxides and the factors that affect the oxidation rate was performed. Based on these studies, a 980 nm wavelength tapered-oxide-apertured structure was grown by molecular beam epitaxy. Devices processed from this growth exhibited a record low threshold current of 125 μA with 59% differential efficiency from a 0.6 μm diameter device. Although the external differential efficiencies remained constant for devices larger than 0.8 μm, the threshold current densities rose sharply with decreasing size. Threshold current models show that this size-dependence of the threshold current density is minimized by localizing the carriers in the active region to the area defined by the aperture. High temperature diffusion techniques were investigated for their feasibility in creating a high bandgap barrier to lateral carrier diffusion around the active region. Studies on impurity-free vacancy disordering, Ga+-ion implantation, and Si+-ion implantation are discussed and conclude that Si +-ion implantation was the best technique for providing the necessary bandgap difference. A study of the effects of high temperature on a dielectric-apertured VCL structure concluded that carbon doping and tapered-air apertures are required in order to minimize degradation of VCL performance during annealing. Using the technique of high-temperature intermixing of ion implanted regions, lateral carrier confinement was demonstrated by the lower threshold current of the implanted structures compared to the un-implanted structures. |
