All-epitaxial mode- and current-confined GaAs-based vertical-cavity surface-emitting lasers
Oxide-confined vertical-cavity surface-emitting laser (VCSEL) emerged as a very attractive light source due to its optical mode-confinement, simultaneous current-confinement, and the resulting low threshold. However, oxideconfinement has serious drawbacks due to the reliability issue and the strain problem among others. In this dissertation, a new all-epitaxial VCSEL with allsemiconductor structure and simultaneous mode- and current-confinement is introduced and aims at attacking the oxide-confined VCSEL limitations. The benefits of the new technology include high performance, reliability, uniformity and the capacity for intracavity patterning. VCSEL performance is mainly determined by how effectively photons and carriers are confined. A lithographically defined intracavity phase-shifting mesa is used for mode confinement. Mesa height and placement in the cavity are carefully considered to achieve excellent optical loss control including both the diffraction loss and the scattering loss. A specially designed VCSEL incorporating the intracavity phase-shifting mesa successfully demonstrates mode-confinement. Selective interfacial Fermi-level pinning is used for currentconfinement. Regrowth on oxidized AlGaAs off the intracavity mesa results in Fermi-level pinning at the interface and a valance band barrier for holes, providing current blocking. Regrowth on oxidized AlGaAs is challenging. Factors considered for surface protection and controlling regrowth surface roughness are: (a) sacrificial layers, (b) the Al ratio in the AlGaAs to be regrown on, and (c) the regrowth temperature. An all-epitaxial mode- and current-confined GaAs-based VCSEL is fabricated and device performance is discussed. The ability to incorporate the intracavity patterns for perfect gain/mode matching and optical mode engineering in the all-epitaxial mode- and currentconfined VCSEL could greatly improve the lasing threshold and mode control. An all-epitaxial VCSEL incorporating the intracavity circular gratings is presented and the device performance is compared to a single intracavity mesa VCSEL fabricated on the same wafer.