We review the family of optoelectronic devices whose performance is enhanced by placing the active device structure inside a Fabry‐Perot resonantmicrocavity. Such resonantcavity enhanced (RCE) devices benefit from the wavelength selectivity and the large increase of the resonant optical field introduced by the cavity. The increased optical field allows RCE photodetector structures to be thinner and therefore faster, while simultaneously increasing the quantum efficiency at the resonant wavelengths. Off‐resonance wavelengths are rejected by the cavity making RCE photodetectors promising for low crosstalk wavelength division multiplexing(WDM) applications. RCE optical modulators require fewer quantum wells so are capable of reduced voltage operation. The spontaneous emission spectrum of RCE light emitting diodes(LED) is drastically altered, improving the spectral purity and directivity. RCE devices are also highly suitable for integrated detectors and emitters with applications as in optical logic and in communication networks. This review attempts an encyclopedic overview of RCE photonicdevices and systems. Considerable attention is devoted to the theoretical formulation and calculation of important RCE device parameters. Materials criteria are outlined and the suitability of common heteroepitaxial systems for RCE devices is examined. Arguments for the improved bandwidth in RCE detectors are presented intuitively, and results from advanced numerical simulations confirming the simple model are provided. An overview of experimental results on discrete RCE photodiodes, phototransistors, modulators, and LEDs is given. Work aimed at integrated RCE devices,optical logic and WDM systems is also covered. We conclude by speculating what remains to be accomplished to implement a practical RCE WDM system.

Resonant cavity enhanced photonic devices

Reflection anisotropy spectroscopy (RAS) is a non-destructive optical probe of surfaces that is capable of operation within a wide range of environments. In this review we trace the development of RAS from its origins in the 1980s as a probe of semiconductor surfaces and semiconductor growth through to the present where it is emerging as a powerful addition to the wide range of existing ultra-high vacuum (UHV) surface science techniques. The principles, instrumentation and theoretical considerations of RAS are discussed. The recent progress in the application of RAS to investigate phenomena at metal surfaces is reviewed, and applications in fields including electrochemistry, molecular assembly, liquid crystal device fabrication and remote stress sensing are discussed. We show that the experimental study of relatively simple surfaces combined with continuing progress in the theoretical description of surface optics promises to unlock the full potential of RAS. This provides a firm foundation for the application of the technique to the challenging fields of ambient, high pressure and liquid environments. It is in these environments that RAS has a clear advantage over UHV-based probes for investigating surface phenomena, and its surface sensitivity, ability to monitor macroscopic areas and rapidity of response make it an ideal complement to scanning probe techniques which can also operate in such environments.

http://iopscience.iop.org/article/10.1088/0034-4885/68/6/R01/pdf

Reflection anisotropy spectroscopy

We review the chemistry, microstructure, and processing of buried oxides converted from AlGaAs layers using wet oxidation Hydrogen is shown to have a central role in the oxidation reaction as the oxidizing agent and to reduce the intermediate predict As/sub 2/O/sub 3/ to As The stable oxide is amorphous (Al/sub x/Ga/sub 1-x/)/sub 2/O/sub 3/ which has no defects along the oxide/semiconductor interfaces but can exhibit strain at the oxide terminus due to volume shrinkage The influence of gas flow, gas composition, temperature, Al-content, and layer thickness on the oxidation rate are characterized to establish a reproducible process Linear oxidation rates with Arrhenius activation energies which strongly depend upon AlAs mole fraction are found The latter produces strong oxidation selectivity between AlGaAs layers with slightly differing Al-content Oxidation selectivity to thickness is also shown for layer thickness <60 nm Differences between the properties of buried oxides converted from AlGaAs and AlAs layers and the impact on selectively oxidized vertical cavity laser lifetime are reported

Advances in selective wet oxidation of AlGaAs alloys

We review the use of specular X-ray reflectivity (XRR) for the characterization of thin-film and surface structures. Specular X-ray scattering at small scattering vectors allows characterization of electron density profiles perpendicular to the surface on the length scale of 0.1 to 100 nm. This allows measurement of surface morphology, thin films, multilayer structures, and buried interfaces. The technique is nondestructive and can be applied in situ in a variety of processing environments. In the first half of the article, we review the theory and methods of XRR, including analysis of XRR spectra by a multilayer optical approach and a discussion of surface roughness measurements by XRR and other techniques. In the second half, we present a wide range of examples of XRR applications in thin-film structures, dynamic processes, liquid surfaces, and macromolecular structures.

Thin film and surface characterization by specular X-ray reflectivity

Nano-scale properties of defects in compound semiconductor surfaces

We report the first time-resolved x-ray scattering study of the homoepitaxial growth of GaAs by organometallic vapor-phase epitaxy. The growth mode was determined to be layer-by-layer by observing ≃1-Hz oscillations of the x-ray intensity from the 11l crystal truncation rod near the 110 position. We show that the spatial distribution of islands can be dynamically determined by measuring the x-ray diffuse scattering near the 110. Finally, we show that significant correlations exist between the locations of islands during layer-by-layer growth

Time-resolved x-ray scattering studies of layer-by-layer epitaxial growth

We have carried out a transmission electron microscopy based study of AlGaAs–Al(oxide) heterolayers created by lateral sidewall wet oxidation and identify the oxide phase formed as a consequence of the oxidation of AlAs to be γ‐Al2O3, with the cubic Fd 3m structure. The oxide‐semiconductor interface is weak and porous, possibly due to the high stress loads developed during oxidation, and we propose that the fast oxidation rates are a consequence of reactants transported to the oxidation front along the porous interface.

Microstructure of AlGaAs‐oxide heterolayers formed by wet oxidation

Atomic scale characterization of organometallic vapor phase epitaxial growth using in-situ grazing incidence X-ray scattering

We show that novel wavelength-sensitive devices can be fabricated by coupling a semiconductor vertical cavity resonator to a low index waveguide. The optical mode in the resonator propagates at an angle, and the resonator resembles a high index waveguide. A taper in the thickness of the resonator allows different parts of the waveguide to operate at different wavelengths. These structures are analyzed using both thin film equations and waveguide normalism. Concentrating on a waveguide demultiplexer, simple design equations are derived, and a demonstration device is fabricated for TE mode at 0.75 /spl mu/m operation. Using AlGaAs/AlAs multilayers and a polymer top waveguide, the spectrometer exhibited a dispersion of 29 nm/cm, a wavelength resolution of better than 1 nm, and an intrinsic device efficiency of about 90%. A similar structure containing a light-emitting quantum well operated as a multiwavelength light source by modifying the spontaneous emission into the polymer waveguide. >

Vertical cavity devices as wavelength selective waveguides

We have used in situ x-ray-scattering techniques to analyze surface reconstructions and ordered steps at various stages in the growth of GaAs by organometallic vapor-phase epitaxy. In contrast to an earlier report of a c(4\ifmmode\times\else\texttimes\fi{}4) reconstruction, our current measurements reveal a related structure with 1\ifmmode\times\else\texttimes\fi{}2 symmetry. The 1\ifmmode\times\else\texttimes\fi{}2 structure is a disordered form of the c(4\ifmmode\times\else\texttimes\fi{}4) reconstruction in which long-range correlations between dimer rows are preserved but dimer vacancies are located at random. Aside from reconstructions, ordered step structures were studied on samples with both high (2.2\ifmmode^\circ\else\textdegree\fi{}) and low (0.07\ifmmode^\circ\else\textdegree\fi{}) levels of miscut. Using Gaussian step-spacing distributions with widths of order the mean terrace size, a numerical model is used to reproduce measured truncation rod profiles in scans perpendicular to steps. We also use the model to follow the narrowing of the step-spacing distribution which occurs during growth. After the growth of several hundred angstroms of GaAs, truncation-rod profiles sharpen, accompanied by a shift in peak positions. The shift is due to an asymmetric weighting of the scattering from terraces of different widths: wide terraces make a greater contribution to the structure factor. For samples with a broadened distribution of step spacings, this effect results in a smaller peak splitting than that which would occur for an ideally miscut sample.

D.W. Kisker

Papers

Time-resolved x-ray scattering studies of layer-by-layer epitaxial growth

Microstructure of AlGaAs‐oxide heterolayers formed by wet oxidation

Atomic scale characterization of organometallic vapor phase epitaxial growth using in-situ grazing incidence X-ray scattering

Vertical cavity devices as wavelength selective waveguides

X-ray-scattering analysis of surface structures produced by vapor-phase epitaxy of GaAs.