O. Blum

Electrical and optical characteristics of AlAsSb/GaAsSb distributed Bragg reflectors for surface emitting lasers

We demonstrate an undoped 20 1/2 pair AlAsSb/GaAsSb distributed Bragg reflector (DBR) grown lattice matched to an InP substrate by molecular beam epitaxy. Reflectivity measurements indicate a stop band centered at 1.78 μm with a maximum reflectivity exceeding 99%. We also measure current–voltage characteristics in a similar 10 1/2 period p‐type DBR and find that a current density of 1 kA/cm2 produces a 2.5 V drop. Hole mobilities and doping concentrations in AlAsSb and GaAsSb are also reported.

HIGHLY REFLECTIVE, LONG WAVELENGTH ALASSB/GAASSB DISTRIBUTED BRAGG REFLECTOR GROWN BY MOLECULAR BEAM EPITAXY ON INP SUBSTRATES

Surface normal optoelectronic devices operating at long wavelengths (≳1.3 μm), require distributed Bragg reflectors (DBRs) with a practical number (≤50) of mirror layers. This requirement implies a large refractive index difference between the mirror layers, which is difficult to achieve in the traditionally used phosphide compounds. We demonstrate a highly reflective AlAsSb/GaAsSb DBR grown nominally lattice matched to an InP substrate by molecular beam epitaxy. Reflectivity measurements indicate a stop band centered at 1.74 μm with maximum reflectivity exceeding 98%, which is well fitted by our theoretical predictions. Atomic force microscopy and transmission electron microscopy indicate reasonable crystal quality with some defects due to an unintentional lattice mismatch to the substrate.

GaAsSb/InGaAs type-II quantum wells for long-wavelength lasers on GaAs substrates

The authors have investigated the properties of GaAsSb/InGaAs type-II bilayer quantum well structures grown by molecule beam epitaxy for use in long-wavelength lasers on GaAs substrates. Structures with layer, strains and thicknesses designed to be thermodynamically stable against dislocation formation exhibit room-temperature photoluminescence at wavelengths as long as 1.43 {mu}m. The photoluminescence emission wavelength is significantly affected by growth temperature and the sequence of layer growth (InGaAs/GaAsSb vs GaAsSb/InGaAs), suggesting that Sb and/or In segregation results in non-ideal interfaces under certain growth conditions. At low injection currents, double heterostructure lasers with GaAsSb/InGaAs bilayer quantum well active regions display electroluminescence at wavelengths comparable to those obtained in photoluminescence, but at higher currents the electroluminescence shifts to shorter wavelengths. Lasers have been obtained with threshold current densities as low as 120 A/cm{sup 2} at 1.17 {mu}m, and 2.1 kA/cm{sup 2} at 1.21 {mu}m.

Wet thermal oxidation of AlAsSb lattice matched to InP for optoelectronic applications

We demonstrate wet thermal oxidation of an AlAsSb layer lattice matched to an InP substrate. Oxidation in an InGaAs/AlAsSb/InGaAs structure proceeds in a lateral direction, producing an oxide layer embedded between two layers of InGaAs. Auger analysis and Raman spectroscopy indicate conversion of the AlAsSb into an aluminum oxide with an elemental antimony layer at the top oxide‐InGaAs interface. Scanning electron microscope cross‐sectional views of partially and fully oxidized samples are also presented.

Refractive index and hygroscopic stability of AlxGa1−xAs native oxides

The authors present prism coupling measurements on Al{sub x}Ga{sub 1{minus}x}As native oxides showing the dependence of refractive index on composition (0.3 {le} x {le} 0.97), oxidation temperature (400 {le} T {le} 500), and carrier gas purity. Index values range from n = 1.490 (x = 0.9, 400) to 1.707 (x = 0.3, 500 C). The oxides are shown to adsorb moisture, increasing their index by up to 0.10 (7%). Native oxides of Al{sub x}Ga{sub 1{minus}x}As (x {le} 0.5) have index values up to 0.27 higher and are less hygroscopic when prepared with a small amount of O{sub 2} in the N{sub 2} + H{sub 2}O process gas. The higher index values are attributed to a greater degree of oxidation of the Ga in the film.

Barrier-layer-thickness control of selective wet oxidation of AlGaAs for embedded optical elements

Selective wet oxidation of AlGaAs layers can be used to form embedded optical elements, such as buried lenses and current control apertures in vertical cavity structures. Oxidation rates of buried Al0.94Ga0.06As layers were controlled by varying the thickness of GaAs barrier layers between layers of Al0.94Ga0.06As and Al0.98Ga0.02As. This phenomenon can be attributed to the superposition of a vertical oxidation component due to species diffusing through the barrier layer and a constant lateral oxidation component. The magnitude of the vertical component is controlled by the GaAs barrier thickness, which determines the concentration of additional oxidizing species in the Al0.94Ga0.06As layer.

Oxidized AlxGa1−xAs heterostructure planar waveguides

Waveguiding by total internal reflection is demonstrated within Al{sub x}Ga{sub 1{minus}x}As semiconductor heterostructures which have been fully oxidized in water vapor at {approximately}490 C. Refractive index, mode propagation constant, propagation loss ({le}3 cm{sup {minus}1}) at {lambda}=1.3 and 1.55 {micro}m, secondary ion mass spectrometry depth profile, and Fourier transform infrared transmission spectra measurements are presented to characterize a multimode single heterostructure oxide waveguide. An index contrast of {Delta}n=0.06 is observed between oxidized x=0.4 and x=0.8 Al{sub x}Ga{sub 1{minus}x}As oxide layers. Absorption loss at 1.55 {micro}m is observed due to OH groups. Near-field images are presented showing waveguiding in a single-mode oxide double heterostructure.

Low-power, parallel photonic interconnections for multi-chip module applications

New applications of photonic interconnects will involve the insertion of parallel-channel links into Multi-Chip Modules (MCMs). Such applications will drive photonic link components into more compact forms that consume far less power than traditional telecommunication data links. MCM-based applications will also require simplified drive circuitry, lower cost, and higher reliability than has been demonstrated currently in photonic and optoelectronic technologies. The work described is a parallel link array, designed for vertical (Z-Axis) interconnection of the layers in a MCM-based signal processor stack, operating at a data rate of 100 Mb/s. This interconnect is based upon high-efficiency VCSELs, HBT photoreceivers, integrated micro-optics, and MCM-compatible packaging techniques.

EPITAXIAL LAYER THICKNESS MEASUREMENT BY CROSS-SECTIONAL ATOMIC FORCE MICROSCOPY

An epitaxial layer thickness measurement technique has been developed using cross‐sectional atomic force microscopy (XSAFM). Cleaved and etched epitaxial heterostructures of Al0.5Ga0.5As/GaAs have been analyzed using this technique. XSAFM analysis of a 20.5 period structure of 300‐A‐thick Al0.5Ga0.5As/GaAs layers agreed to within 2% of x‐ray diffraction data. XSAFM analysis of a structure consisting of GaAs wells ranging from ∼15 to 600 A with 300 A Al0.5Ga0.5As barriers was also performed. The XSAFM measured well thicknesses agreed quite well with photoluminescence (PL) measurements taken at 4 K. XSAFM can thus serve as a rapid alternative to conventional thickness measurement techniques such as SEM and TEM.

Fully-oxidized AlGaAs heterostructures as broadband passive waveguides for photonic circuit integration

In this paper, we demonstrate propagation losses of less than /spl alpha/=1.0 cm/sup -1/ at both /spl lambda//sub 0/=1.55 and 0.63 /spl mu/m for an oxidized Al/sub 0.3/Ga/sub 0.7/As/Al/sub 0.85/Ga/sub 0.15/As waveguide. These loss reductions, and the realization of transparency well above the GaAs band edge, are achieved through both an improved structure (thicker cladding layer, larger Al composition contrast) and a modification to the standard oxidation process (via the controlled addition of O/sub 2/). The addition of trace amounts of oxygen reduces the oxide surface roughness, increases the index of oxidized Al/sub x/Ga/sub 1-x/As (x<0.5), and increases oxidation rates (0.3<x<0.85). These process enhancements lead to improved mode confinement and reduced absorption and scattering losses.