R. L. Thornton

Ultrahigh light transmission through a C-shaped nanoaperture

Optical resolution beyond the diffraction limit can be achieved by use of a metallic nanoaperture in a near-field optical system. Conventional nanoapertures have very low power throughput. Using a numerical finite-difference time domain method, we discovered a unique C-shaped aperture that provides approximately 3 orders of magnitude more power throughput than a conventional square aperture with a similar near-field spot size of approximately 0.1 lambda. Microwave experiments at 6 GHz quantitatively confirmed the simulated transmission enhancement. The high transmission of the C-aperture--or one of the related shapes--is linked to both a propagation mode in the aperture and local surface plasmons.

Stripe‐geometry quantum well heterostructure AlxGa1−xAs‐GaAs lasers defined by defect diffusion

Impurity‐free selective layer disordering, utilizing Si3N4 masking stripes and SiO2 defect (vacancy) sources, is used to realize room‐temperature continuous AlxGa1−xAs‐GaAs quantum well heterostructure lasers.

Effects of dielectric encapsulation and As overpressure on Al‐Ga interdiffusion in AlxGa1−x As‐GaAs quantum‐well heterostructures

Data are presented showing that the Al‐Ga interdiffusion coefficient (DAl‐Ga) for an AlxGa1−xAs‐GaAs quantum‐well heterostructure, or a superlattice, is highly dependent upon the crystal encapsulation conditions. The activation energy for Al‐Ga interdiffusion, and thus layer disordering, is smaller for dielectric‐encapsulated samples (∼3.5 eV) than for the case of capless annealing (∼4.7 eV). The interdiffusion coefficient for Si3N4‐capped samples is almost an order of magnitude smaller than for the case of either capless or SiO2‐capped samples (800≤T≤875 °C). Besides the major influence of the type of encapsulant, the encapsulation geometry (stripes or capped stripes) is shown, because of strain effects, to be a major source of anisotropic Al‐Ga interdiffusion.

Strained Ga/sub x/In/sub 1-x/P/(AlGa)/sub 0.5/In/sub 0.5/P heterostructures and quantum-well laser diodes

The properties of (AlGa)/sub 0.5/In/sub 0.5/P, strained Ga/sub x/In/sub 1-x/P/(AlGa)/sub 0.5/In/sub 0.5/P heterostructures, and single quantum well (QW) laser diodes with Al/sub 0.5/In/sub 0.5/P cladding layers, prepared by low pressure organometallic vapor phase epitaxy, are described. The influence of biaxial strain upon the relative positions of the valence band edges are examined by analyzing the polarized spontaneous emission. Laser diodes with wavelength 620 >

Drift leakage current in AlGaInP quantum-well lasers

The temperature dependence of threshold current and quantum efficiency for Ga/sub x/In/sub 1-x/P (x=0.4, 0.6; lambda =680, 633 nm) single 80-AA quantum-well lasers is compared and analyzed using a model for the electron leakage current. This model fits the experimental data well, correctly describing the rapid increase in threshold and drop in quantum efficiency as temperature increases. Also, it indicates that the drift (rather than diffusion) component of the electron leakage current, is dominant, because of the poor p-type conductivity in AlGaInP. >

Monolithic waveguide coupled cavity lasers and modulators fabricated by impurity induced disordering

Describes results on AlGaAs integrated optoelectronic devices consisting of combinations of buried passive waveguide regions with active multiple quantum well gain regions. The authors have developed a technique for accomplishing this integration in which the waveguide regions have greatly reduced propagation loss at the gain wavelength of the active media. They have incorporated sections of waveguide into laser cavities, and the resulting low (7-11 mA) threshold currents and weak dependence of threshold current on waveguide length confirm the reduced loss and waveguiding nature of the waveguide regions. They have used these structures to monolithically couple laser amplifiers to electroabsorption modulators. Among their results on these devices are electroabsorption modulators with contrast ratios of 23:1 and monolithic Q-switch operation resulting in pulse widths of less than 200 ps. The relative simplicity with which these structures are fabricated via impurity induced disordering techniques promises to result in major impact on practical systems for monolithic integration. >

Low threshold planar buried heterostructure lasers fabricated by impurity‐induced disordering

We report on the fabrication of index‐guided buried heterostructure lasers by the process of silicon impurity‐induced disordering. This fabrication process for a buried heterostructure laser offers the advantage of reduced fabrication complexity over previous fabrication methods. We present measurements that demonstrate the operation of these devices in a single longitudinal mode, fundamental transverse mode, and with cw threshold currents as low as 3 mA. We also have extracted 80 mW cw from a device with a 10‐mA threshold current. Our results indicate that this process has great potential for the fabrication of low threshold, efficient light sources.

Low-threshold disorder-defined buried-heterostructure AlxGa1−xAs-GaAs quantum well lasers

Two different quantum well heterostructure wafers are used to fabricate buried‐heterostructure AlxGa1−xAs‐GaAs quantum well lasers using Si‐induced layer disordering (via Si diffusion). In contrast to the first wafer (QWH1), the second quantum well wafer (QWH2) utilizes Zn instead of Mg as the p‐type dopant in the top AlxGa1−xAs confining layer and yields, because of concentration mismatch in acceptor and donor doping in the confining layers (nZn>nSe), inferior laser diodes owing to Zn diffusion from the p‐type to the n‐type confining layer during high temperature processing (850 °C Si diffusion). The first quantum well heterostructure, however, employs a lower concentration Mg doping for its p‐type confining layer (nMg<nSe) and yields high performance devices when used with the Si‐induced layer‐disordering process. For QWH1 the p‐n junction and injection is not displaced (as for QWH2) from the QW active region during Si‐induced layer disordering (850 °C annealing). A fabrication process is presented in w...

Planar laterally oxidized vertical-cavity lasers for low-threshold high-density top-surface-emitting arrays

We introduce a novel device architecture that enables the fabrication of low threshold high density vertical-cavity surface-emitting laser (VCSEL) arrays. Our structure relies on a group of small via holes to access a buried AlGaAs layer for lateral oxidation. In contrast to the conventional method of exposing mesa sidewalls through etched pillars, this technique provides our VCSELs with the benefits of oxide confinement without sacrificing wafer planarity. Maintaining wafer planarity is essential for the easy fabrication and contacting of densely packed devices. The devices operate at 827 nm, with a minimum threshold current of 200 /spl mu/A, and a maximum output power of 3.15 mW.

Excitation of a higher order transverse mode in an optically pumped In0.15Ga0.85N/In0.05Ga0.95N multiquantum well laser structure

We report a comparison between measured and calculated far field data for an optically pumped In0.15Ga0.85N/In0.05Ga0.95N multiquantum well laser structure with AlGaN cladding layers. Optical pumping of the semiconductor device was performed with a pulsed 337 nm N2 laser, whose beam was focused to a narrow stripe. A thin upper cladding layer allowed efficient pumping of the In0.15Ga0.85N/In0.05Ga0.95N laser structure. Despite high distributed cavity losses of at least 30 cm−1, and although gain occurred in the small active region only, the seventh order transverse mode was supported in a waveguide formed by the entire 5-μm-thick epitaxial layer structure. Excellent agreement is demonstrated between measured and calculated far field patterns of the lasing mode.