K. A. Stair

Waveguide-coupled AlGaAs/GaAs microcavity ring and disk resonators with high finesse and 21.6-nm free spectral range

We report the realization and demonstration of novel semiconductor waveguide-coupled microcavity ring and disk resonators. For a 10.5-microm-diameter disk resonator, we measure a finesse of 120, a resonant linewidth of 0.18 nm, and a free-spectral range of 21.6 nm in the 1.55-mum-wavelength region. We present the nanofabrication methods and the experimental results for 10.5- and 20.5-mum-diameter ring and disk resonators to show the feasibility of such devices.

Thickness modulation of InGaAs/GaAs superlattices studied by large angle x‐ray scattering

Superlattices of 100‐period InxGa1−xAs (15 A)/GaAs(100 A) grown on GaAs (100) substrates by molecular beam epitaxy were studied by using large angle x‐ray scattering techniques. In contrast to the usual superlattice satellite peaks corresponding to structural periodicity along the growth direction, unusual satellite peaks in the lateral direction parallel to the sample surface were observed in a sample with x=0.535 grown at 480 °C, indicating an in‐plane ordering. This result is confirmed by high resolution transmission electron microscopy observations that thickness modulation in the InxGa1−xAs layers gives rise to long‐range lateral periodic arrays of clusterlike microstructures with spacing on the order of a few hundred angstroms. This thickness modulation is found to occur only in the [110] direction, thus the material can be viewed as a somewhat disordered array of grown‐in parallel quantum wires.

Evidence of room‐temperature exciton by magnetophotoreflectance in epitaxial GaAs and quantum well structures

Photoreflectance experiments with magnetic fields up to 14.5 T are performed on epitaxial GaAs and GaAs/Ga1−xAlxAs quantum well samples at room temperature and 2 K. Our experiments show unique and direct evidence that photoreflectance structures are excitonic transitions in all of the above cases.

Temperature tuning of microcavity ring and disk resonators at 1.5-/spl mu/m

We report the temperature-tuning of novel microcavity resonators with wide free spectral range /spl Delta//spl lambda//sub fsr/, and high finesse. We have fabricated and demonstrated AlGaAs/GaAs ring and disk resonators with diameters of 10.5 and 20.5 /spl mu/m evanescently coupled to single-mode waveguides. Strong lateral waveguide confinement allows micron-size cavities with negligible bending loss and the resonators can be fabricated with reasonably low loss using nanofabrication techniques, resulting in a high finesse. The 10.5-/spl mu/m-diameter disk resonator yields a finesse as high as 120 (Q=8600) and /spl Delta//spl lambda//sub fsr/ of 21.6 nm. The temperature tuning is 1.3 nm/10/spl deg/C, suitable for a thermally-controlled switch or widely tunable filter.

GaAs/Al/sub x/Ga/sub 1-x/As superlattice waveguide absorption modulators with very low drive voltage

The first GaAs/Al/sub x/Ga/sub 1-x/As superlattice waveguide absorption modulators operating at approximately 860 nm that utilize the Wannier-Stark effect are reported. The n=-1 Stark ladder peak, which is the transition from the valence band well to the nearest neighbor conduction band well, is used. This peak shifts rapidly with applied electric field, resulting in drive voltages lower than can be achieved using the quantum-confined Stark effect for quantum-well waveguides of similar structure. For a 1000- mu m-long waveguide at 867 nm, the authors obtain an extinction ratio of approximately 20 dB and a 4-dB attenuation with a drive voltage of 2 V.<<ETX>>

The monolithic integration of a superluminescent diode with a power amplifier

Monolithic integration of a superluminescent diode with a tapered semiconductor power amplifier is proposed. The basic operation of the integrated optical source is demonstrated under pulse conditions. Output power obtained by the integrated device is one to two orders of magnitude higher than the conventional superluminescent diode (SLD) devices.

Fermi-level pinning and growth characteristics of Au on InP(111)

Abstract Atomically clean phosphorus-enriched InP( 1 1 1 ) surfaces have been produced by argon sputtering and subsequent annealing in a phosphorus ambient. Pinning of the surface Fermi level at a position 1.10 eV above the valence band maximum has been observed on clean, well-annealed InP( 1 1 1 ). In addition, a range of surface Fermi levels from 0.70 to 1.10 eV above the valence band maximum has been observed for various InP( 1 1 1 ) surfaces as a function of annealing temperature and degree of stoichiometry. For a well-annealed InP( 1 1 1 ) surface, the Fermi level position after gold deposition appears to saturate at a position 0.70 eV above the valence band maximum. We interpret these results in terms of multiple defect levels in the bandgap. Observations of In4d and Au4f photoemession peaks demonstrate both the dissociation of InP and intermixing between gold and the substrate. Photoemission of adsorbed xenon further indicates that intermixing occurs without formation of Au clusters.

Temperature Dependence of Optical Properties of AlAs, Studied by In Situ Spectroscopic Ellipsometry

The dielectric functions e = e1+ie 2 of AlAs were determined from 1.5 eV to 5.0 eV, by spectroscopie ellipsometry (SE), from room temperature (RT) to ∼577 °C in an ultrahigh vacuum (UHV) chamber. Molecular beam epitaxy (MBE)-grown AlAs was covered by a thin GaAs layer, which was passivated by arsenic capping to prevent oxidation. The arsenic cap was desorbed inside the UHV chamber. SE measurements of the unoxidized sample were made, at various temperatures. Temperature dependent optical constants of AlAs were obtained by mathematically removing the effects of the GaAs cap and substrate. Quantitative analyses of the variations of critical-point energies with temperature, by using the harmonic oscillator approximation (HOA), indicate that the E 1 and E 1 +Δ 1 energies decrease -350 meV as temperature increases from RT to 500 °C.

Measurement of the refractive index of AlxGa1-xAs and the mode indices of guided modes by a grating coupling technique

We have determined the index of refraction of AlxGa−xAs over the wavelength range 0.76–1.15 μm, and the composition range 0≤x<0.33, using a grating to couple light into waveguides. We find the mode indices of multimode slab waveguides from the coupling angle and grating period, then calculate the bulk indices of the core and cladding materials by a root searching technique using the analytical formula for the effective index of a guided mode. The method gives the core index within ±0.001, and the cladding index within ±0.01. We are in agreement with high precision index values for GaAs in the literature, confirming the method. We are in substantial agreement with literature values for AlGaAs but find a significant systematic difference in the composition dependence. An analysis of measurement uncertainties shows that the determination of composition is the dominant variable.

Electric field‐induced optical waveguide intensity modulators using GaAs/AlxGa1−xAs quantum wells

We demonstrate a new waveguide intensity modulator that uses the field‐dependent refractive index change associated with quantum wells to control the lateral confinement of light in a slab waveguide. By operating at photon energies ∼40 meV below the zero field electron–heavy hole transition energy, we show, conclusively, that the field‐induced refractive index change is primarily due to the quantum‐confined Stark effect. Intensity modulators are demonstrated with on/off ratios better than 3:1. Devices based on this electrically controllable lateral confinement will play an important role in integrated optics.