Epitaxial regrowth based fabrication process for vertical cavity lasers

GaAs based oxide confined vertical-cavity surface-emitting lasers (VCSELs) have demonstrated record performance in terms of low threshold current, high modulation speed and high wall-plug efficiency. However, oxide-confined VCSELs have reliability and non-uniformity problems that limit scaling to small active volumes for single mode operation or to micro-cavity dimensions for quantum light sources. The optical mode is also difficult to engineer since aperture geometries are limited. These limitations call for the development of a new technology that provides full control of modal overlap with optical gain, and this requires patterning of the VCSEL’s transverse mode- and current-confinement. A new approach presented in this dissertation demonstrates a very important attribute in providing lithographically defined and self-aligned mode- and current-confinement suitable for arbitrary patterning and size scaling, and for high reliability, is based on an all-epitaxial device. The fabrication process involves epitaxial regrowth over shallow mesas to incorporate these intra-cavity patterns that have direct overlap with the optical mode. These intracavity gratings are defined by lithography and a selective etching process after the first stage of epitaxial growth. In this work, a VCSEL with an intracavity grating has been realized that shows an increase in the slope efficiency due to better matching of the gain and optical mode in comparison to a device that lacks the grating. Using a similar regrowth process, a laser diode incorporating a buried high index contrast GaAs-air (etched void) photonic pattern within the cavity has also been demonstrated. Epitaxial quantum dots (QDs) present new opportunities in semiconductor light sources due to their charge localization and modified electronic density of states. It is especially interesting to combine QDs with a microcavity VCSEL, since electronic and photonic confinement become scalable in a device that can have important commercial applications. This has been achieved in a buried heterostructure VCSEL that employs an intracavity mesa to confine the quantum dots and optical mode to the same regions in the cavity. Cavity quality factors as high as 33000 are measured, and ground state lasing is demonstrated with a single quantum dot active layer for temperatures up to 110 K.