Selective oxidation of aluminum-bearing III-V semiconductors: Properties and applications to small-volume quantum well heterostructure lasers.

摘要

In this work, the water-vapor oxidation of Al-bearing III-V compound semiconductors is used to fabricate small-volume semiconductor light-emitting devices. The oxidized material, native to the crystal, is mechanically and chemically stable. In addition, it is electrically insulating and has a low refractive index making it useful for defining optical cavities and current paths. The oxidation rate is sensitive to the Al composition of the material, permitting selective oxidation of "buried" high-Al-composition layers.; The selective oxidation of "buried" layers is used in this work to fabricate laser cavities that are small in volume. Small-volume cavities, called microcavities, are known to exert control over the recombination of carriers within the cavity, and may be exploited to create devices with improved laser characteristics. In this work, the embedded oxide is used to form the distributed Bragg reflecting (DBR) mirrors of a vertical-cavity surface-emitting laser (VCSEL), resulting in a very high index-contrast mirror and, consequently, a very compact VCSEL cavity that exhibits microcavity effects very strongly.; Another form of microcavity, the microdisk laser, is fabricated using the oxide process. The microdisk laser (10 {dollar}mu{dollar}m in diameter) rests on the low-index, thermally conductive native oxide and exhibits laser modes characteristic of "whispering gallery" modes propagating around the perimeter of the disk. Low threshold pump intensities indicate that these microdisk lasers are high-Q cavities.; By combining impurity-induced layer disordering (IILD) with the oxidation process, a planar minidisk laser is fabricated. The minidisk laser is larger in diameter (37 {dollar}mu{dollar}m) and is entirely planar. The minidisk laser operates in "whispering gallery" modes around the perimeter of the disk, indicating the feasibility of the combination of processes in fabricating disk lasers.; The same IILD + oxidation process is used to fabricate a two-dimensional active photonic lattice that is comprised of {dollar}sim{dollar}9-{dollar}mu{dollar}m microdisk lasers that are arranged in a triangular (hexagonal close-packed) lattice arrangement. The disks are closely spaced (11-{dollar}mu{dollar}m center-to-center spacing) such that they are strongly coupled. As a result of the coupling of the disks, the photonic lattice exhibits laser operation in bands of energy located around the microdisk modes. In addition, the photonic lattice emits beams of energy along six symmetrical "crystal" directions. The details of photonic lattice fabrication and characterization are described.