All epitaxial mode and current confined semiconductor laser using selective fermi level pinning
This dissertation presents a new lithographically defined approach to form self-aligned mode- and current-confined all-epitaxial GaAs-based VCSELs and quantum dot lasers. The mode confinement mechanism by intracavity phase shifting mesa is verified by a specially designed mode confined VCSEL, which shows the lasing peaks only on the phase shifting mesa with relatively low threshold current density. The current-confining mechanism, which is self aligned with mode confining phase shifting mesa using selective Fermi-level pinning is verified with the test structure with the same active layers in the cavity by substantially increasing the turn on voltage of the region outside mesa. The mode- and current-confined VCSEL also shows improved slope efficiency and lasing spectrum which indicate the only lasing on the mesa region throughout the entire operation range. All-epitaxial, fully planarized mode- and current-confined VCSELs, which have only single phase shifting mesa and surrounding current blocking regions are successfully demonstrated with considerably improved efficiency and threshold current density. As an important application of this technology, all- epitaxial index- and current-confined quantum dot laser is demonstrated. The performances of quantum dot laser shows ground state lasing and stable operation up to high input current of 1.5 A. Extracted waveguide loss indicates additional loss is coming from the current blocking hetero-interfaces which can be reduced by optimization of regrowth condition.