Vertical cavity surface emitting lasers (VCSELs) are demonstrated with high-index-contrast native-oxide-based (AlxOy) distributed Bragg reflectors (DBRs) on both sides of a “2λ” cavity, thus creating a compact (thin, ∼2.8 μm) laser structure. Selective oxidation of high Al composition AlxGa1−xAs layers yields a structure with a four period upper AlxOy/GaAs DBR, a 5.5 period lower AlxOy/GaAs DBR, and a buried oxide current aperture. A reverse-biased tunnel contact junction provides hole injection via lateral electron current between the upper DBR and the oxide aperture layer. These VCSELs operate with submilliampere thresholds, high spontaneous efficiencies, and excellent polarization control.

Al x Ga 1−x As–GaAs–In y Ga 1−y As quantum well heterostructure lasers with thin sharply defined cavities that operate longitudinally or vertically are demonstrated. Longitudinally, the cavity is defined by cleaving (edge emission) while vertical definition is provided by a lower AlxOy/GaAs distributed Bragg reflector (DBR) and an upper SiO2/Si DBR that form a resonant structure. A reverse-biased tunnel contact junction provides lateral electron current to support hole injection through a native-oxide-defined aperture. This ultrathin cavity configuration produces low threshold high efficiency (η∼91%, L=140 μm) edge emission (longitudinal operation) in the case of long lasers (L≳90 μm), and vertical emission for shorter lasers (L≲65 μm). The transition from longitudinal to vertical laser operation as a function of cavity length, L, is demonstrated.

The problems associated with constructing AlxGa1−xAs native-oxide-based distributed Bragg reflectors (DBRs) for vertical cavity surface emitting lasers are investigated. Reflection and stability measurements are performed on structures with central λ/2 cavities (λ∼980 nm) of GaAs surrounded by two periods of native-oxide-based DBRs on the top and 2.5 periods on the bottom. Prior to crystal oxidation (H2O vapor+N2, 430 °C) a period of the DBRs consists of a ∼λ/4 optically thick layer of GaAs and a thicker (oxidation) layer of AlxGa1−xAs (x=0.95, 0.96, 0.97, 0.98, 1.00) surrounded by thinner (∼100 Å) buffer layers that are AlyGa1−yAs (y=0, 0.25, 0.50, 0.65, 0.070, 0.75, 0.80, 0.85). The DBRs are formed after oxidation of the high Al composition AlxGa1−xAs layers, and to some extent the AlyGa1−yAs buffer layers, forming a ∼λ/4 optically thick layer of the native oxide. For comparison, more complicated DBRs are created by oxidizing superlattice layers. It is found that the AlxGa1−xAs composition, x, of the oxidation layer, choice of oxidizing or nonoxidizing AlyGa1−yAs buffer layers (y), oxidation parameters, and post-processing parameters determine the DBR quality and stability, as well as the possibility of reoxidation.

Al x Ga 1−x As-GaAs-In y Ga 1−y As quantum well heterostructure (QWH) lasers with p+-n+ GaAs–InyGa1−yAs reverse-biased tunnel junctions (hole sources) located in the upper cladding of standard lasers and in oxide-defined cavities (requiring lateral bias currents) are demonstrated. The tunnel junctions, introduced to aid lateral current spreading, are grown at different distances from the waveguide active region in a standard QWH structure to determine first the effect of heavily doped tunnel layers on laser threshold currents. Other QWH laser crystals are oxidized to form oxide-aperture devices with, in addition, either a top confining oxide or a top and bottom oxide confining layer. Hole injection is provided between the oxide layers with the aid of the tunnel contact junction and lateral electron current. The buried tunnel contact junction is shown to be an effective method to make possible hole injection via a lateral electron current, with only a modest increase (a small penalty) in voltage drop and series resistance compared to standard devices.

Vertical cavity surface emitting lasers (VCSELs) are demonstrated with reverse-biased tunnel contact junctions allowing low-loss lateral electron current to support hole injection. A compact hybrid vertical cavity is employed consisting of a lower 6.5 period AlxOy/GaAs distributed Bragg reflector (DBR) formed by selective oxidation of high Al composition AlxGa1−xAs, and an electron-beam deposited 5 period SiO2/Si upper DBR. The cavity (active region) is defined also by selectively oxidizing a current-confining aperture. Lateral electron current drives a tunnel contact junction providing hole injection underneath the upper DBR through the oxide-defined current aperture. The p-type crystal in the VCSEL is reduced to a minimum, thus reducing resistive loss and device voltage.

Data are presented on the laser operation of photoexcited active hexagonal photonic lattices consisting of a GaAs–AlAs superlattice slab waveguide patterned with Zn-disordered AlGaAs posts that are converted to oxide. The semiconductor-oxide-post photonic lattice structure lases without the benefit of cleaved edges or other reflecting interfaces owing to strong local optical feedback provided by the high refractive index contrast between oxide posts and the active GaAs–AlAs superlattice. As the pump area is increased at constant pump power, the threshold intensity decreases as higher Q modes in an effectively larger cavity are excited. Similar hexagonal photonic lattices with nonoxidized posts (disordered AlGaAs posts) operate as lasers, but only with the assistance of cleaved edges and by shifting to longer wavelength. The oxide post photonic lattice is compatible with current-driven photonic lattice lasers or active filters.

Data are presented on the planar (top–down) oxidation of graded AlxGa1−xAs upper confining layers of quantum well heterostructures in order to realize high resolution square-edge lasers (or waveguides). A model is developed to facilitate composition grading of AlxGa1−xAs for vertical-wall (square corner or edge) planar oxidation at convenient oxidation times and tolerances. A simple AlGaAs–GaAs quantum well laser structure is used to demonstrate the square-wall (square-corner) planar oxidation method.

Data are presented on the room temperature photopumped laser operation of GaAs–AlAs superlattice microrings in single, coupled pair, and coupled hexagonal-ring configurations. The lasers are fabricated from a GaAs–AlAs superlattice (Lz∼30 Å, LB∼70 Å) that is selectively disordered and deep oxidized (H2O vapor + N2) through its entire thickness to form high-index- contrast planar microrings (11 μm o.d., 3 μm i.d.). Thresholds are ∼1.7×105 W/cm2 (∼150 mW, pump power) for single microrings and 4.3×105 W/cm2 for the pair and hexagonal-ring geometries. Single, coupled pair, and even-numbered coupled microrings arranged in a ‘‘ring’’ (circular) configuration exhibit multiple single modes or more typically twin modes at microring whispering-gallery mode spacings. Microrings are of interest as basic elements in more extended photonic structures, and should be compatible with diode operation of micro lasers.

Data are presented demonstrating the effect that cavity length, and thus Q, has upon quantum well heterostructure edge-emitting laser diodes that are reduced to microcavity thickness. The lasers, with reduced mode density and enhanced spontaneous emission, are defined vertically by a Ag top-contact mirror and a closely spaced (∼0.9 μm) high-contrast AlAs native oxide-GaAs distributed Bragg reflecting bottom mirror. For shorter and shorter diode lengths (700→70 μm, and still lesser mode density) the light versus current (L–I) characteristic below threshold is at first steeper and steeper (amplified stimulated emission), until, at a diode length of ∼100 μm, the loss in Q and insufficient gain are manifest as a downward bend in the L–I curve and a shift to higher threshold current where bandfilling to a higher state (shorter wavelength) contributes more gain.

Data are presented demonstrating double injection and negative resistance in stripe-geometry oxide-aperture AlyGa1−yAs–GaAs–InxGa1−xAs quantum well heterostructure lasers. The buried oxide laser structures are defined, in current and cavity, by laterally oxidizing the higher Al composition upper and lower cladding layers from a mesa edge (a ridge), thus, forming a narrow oxide-defined buried aperture (∼2μm). Post fabrication annealing (425 °C in N2) removes the negative resistance, indicating that the crystal growth and oxidation processes introduce products such as H and OH in the active region that compensate the dopants.

Data are presented demonstrating edge-emitting laser diode operation of AlyGa1−yAs– GaAs–InxGa1−xAs quantum well heterostructures modified by the formation of a buried native-oxide distributed Bragg reflecting (DBR) mirror adding vertical confinement to the longitudinal laser cavity. The bottom DBR mirror, combined with the highly reflective top p-contact metallization (Ag), forms a thin broadband vertical cavity. The auxiliary vertical mirrors are tuned to improve the coupling of the spontaneous emission to the longitudinal lasing mode, resulting in reduced threshold currents and modified emission characteristics below threshold.