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Selectively oxidized vertical cavity surface emitting lasers (VCSELS) have been studied by spectrally resolved near field scanning optical microscopy (NSOM). We have obtained spatially and spectrally resolved images of both subthreshold emission and lasing emission from a selectively oxidized VCSEL operating at a wavelength of 850 nm. Below threshold, highly local high gain regions, emitting local intensity maxima within the active area, were observed; these were found to serve as lasing centers just above threshold. Above threshold, the near field spatial modal distributions of low order transverse modes were identified by spectrally analyzing the emission; these were found to be complex and significantly different from those measured in the far field.

We report Raman imaging of stress in a SiGe/Si optical channel waveguide structure. The difference in thermal expansion coefficients between a Si3N4 stripe and a SiGe layer creates a significant localized stress profile beneath the stripe, which can result in optical confinement suitable for optical waveguide fabrication. We image these areas utilizing Raman polarization selection rules for two transverse optical phonons, relate the Raman peak shifts to strain components, and then to refractive index changes via the photoelastic effect. These micro-Raman images provide spatially resolved two-dimensional refractive index information on the waveguiding region of a channel waveguide structure.

Imaging local index variations by using a form of modulated near-field scanning optical microscopy is suggested. To test these ideas, we have probed two different optical structures, one a well-characterized BK-7 glass prism in the total internal reflection configuration, and the other a side-polished optical fiber waveguide with a step index of refraction of 4.5×10−3. Using a recently developed tapping-mode tuning-fork near-field scanning optical microscope, we have obtained images showing distinct local index variations. This method may have applicability to the characterization of a wide variety of optical waveguide structures.

We use micro- and nano-photoluminescence to study the temperature-dependent excitonic emission from CdSe quantum dots embedded in a ZnSe matrix. By varying the spatial resolution from 200 nm to 1.7 μm, we are able to study the temperature dependence of the ultranarrow (∼200 μeV) emission from excitons confined to single quantum dots, as well as statistical ensembles of up to 200 dots. By measuring the quenching of the photoluminescence (PL) with temperature, we find compelling evidence that the PL emission from these samples results from two different kinds of states. Similar to previous work, we find that a broad PL line persists to 300 K with an activation energy of ∼40 meV. However, we find that the ultranarrow lines are quenched at about 60 K, indicating an effective activation energy of only 4.0 meV.

We have investigated the evolution of molecular beam epitaxy (MBE)-grown, CdSe self-assembled quantum dots on ZnSe surfaces using microphotoluminescence techniques. Bare CdSe dots at room temperature undergo Ostwald ripening over a time scale measured in days. At the elevated temperatures maintained for MBE growth and dot formation, ripening is expected to progress much faster. Capping the dots with a thin ZnSe layer “freezes” the ripening, allowing one to sample different stages of the dot evolution and subsequent characterization. We have grown eleven samples, each with a different time interval, or growth interruption, between dot formation and capping; the growth interruption times ranging from 0 to 300 s, during which the samples were kept at 300 °C. Using microphotoluminescence spectroscopy, we have resolved the sharp emission peaks due to individual dots in each sample and, by analyzing the ensemble characteristics, have identified a new regime in the evolution of CdSe dots.

Single crystal 3C–SiC platelets, formed by thermal decomposition of methyltrichlorosilane at 1650–1750 °C, have been characterized in terms of structure and morphology. The platelets are ∼3–5 mm in length and 1–1.5 mm in thickness. The (111) C face of the crystal, which has an effective zero growth rate, presents a large, mirrorlike surface in the as‐grown 3C crystals. Atomic force microscopy indicates that these as‐grown surfaces are extraordinarily flat and uniform, with a mean surface roughness of 1–2 A. This value is comparable with the roughness of state‐of‐art polished Si wafers. X‐ray rocking curves of the 〈111〉 peak were obtained with a linewidth of 12.3 arcsec. This is the smallest value reported to date for any polytype of SiC. Raman spectroscopy at 300 K reveals a very sharp TO–phonon peak at 797.8 cm−1, with a linewidth of 2.1 cm−1.

We present results of near field scanning optical microscopy measurements performed on single mode AlGaAs ridge channel waveguides. The optical intensity distribution just above the surface of the waveguide structure has been measured by scanning a tapered, aluminum‐coated, fiber probe transverse to the waveguide propagation direction. Experimental results are compared with model calculations performed using both the effective index and beam propagation methods. An accurate description of submicron features in the intensity profile near the ridge edges, as well as the magnitude of the field outside the channel, requires the use of the beam propagation method.

The chemical composition and microstructure of SiC composite fibers were studied by spatially resolved Raman spectroscopy. The spectra display a strong peak in the outer SiC layer identified as a Si signature and thus provide direct evidence of the presence of excess Si in the fiber composites. The Si crystallite size as well as the stress in the Si were estimated. Excess silicon has been previously suggested as the cause of the unusual creep and the anomalous thermal expansion behavior of these composites at high temperatures.

GaAs quantum well (QW) lasers with distributed Bragg reflection (DBR) Al0.3Ga0.7As/GaAs superlattice gratings have been fabricated by the single‐step, maskless focused ion beam (FIB) mixing. 200 keV Si++ FIB implantation with a beam diameter of ∼60–70 nm and a dose of 1014 cm−2 was used to obtain localized compositional mixing. The DBR grating period was 350 nm, corresponding to a third order grating matched to the emission from the 30 nm wide QW. Lasing operation was examined by optical pumping. With a pumping power 1.6× the threshold value, lasing modes were observed near 827 nm, with a spacing of 3 A and a linewidth of 1.5 A.

Polycrystalline diamond films have been grown on silicon at substrate temperatures down to 300 °C in a 3 Torr CH4–H2–O2 microwave plasma. The diamond films exhibit characteristic 1333 cm−1 Raman phonon peaks with linewidths of 3–7 cm−1 and a small nondiamond carbon response. Low temperature diamond synthesis was enhanced by applying a static magnetic field to increase gas dissociation and ionization, and by pulse modulating the 2.45 GHz input microwave power to provide a large atomic hydrogen supply without accompanying positive ion bombardment over most of the discharge cycle. Diamond quality is improved and growth rates are at least an order of magnitude higher in the pulsed mode, compared to continuous wave operation with the same average input microwave power.

Near field microscopy is used to investigate the guided mode intensity distribution of optical channel waveguides and directional couplers with subwavelength spatial resolution. The directional coupler consisted of two single mode optical ridge channel waveguides formed with silicon nitride deposited on a lower cladding layer of SiO2 on a silicon substrate. A near field measurement of the guided mode intensity profile in the transverse direction parallel to the waveguide surface was performed across one of the optical channel waveguides. These variations are compared with model calculations. Similar transverse measurements of light propagating through a directional coupler were performed at many locations along the coupler, providing a view of the evolution of optical power transfer.

Multivariable statistically designed experiments have been used to optimize diamond growth in a H2‐CH4‐O2 magnetoactive plasma at 1–3 Torr total pressure. The input process parameters included total pressure, microwave power, substrate temperature, methane and oxygen fractions, and applied substrate bias, and the experimental response outputs were diamond film growth rate and crystallinity. A clearly defined characteristic 1333 cm−1 Raman peak with a 5 cm−1 full width at half‐maximum identified the optimum diamond crystal growth conditions of H2 (75%)‐CH4 (13%)‐O2 (12%), 3 Torr total pressure, and 650 °C substrate temperature.

High quality diamond films have been grown at low temperature (540–650 °C) and low pressure (2–20 Torr) in a microwave electron cyclotron resonance CH4‐O2‐H2 discharge. The films were characterized by microprobe Raman spectroscopy and scanning electron microscopy. Diamond crystals grown at ∼600 °C and 10 Torr with 2% oxygen exhibit a characteristic Raman peak at 1334 cm−1 with no accompanying nondiamond carbon peaks.

We report on the use of a Raman microprobe to investigate the nonlinear optical process of polarization rotation in Ti:LiNbO3 optical channel waveguides. Selection rules allow the Raman scattered signal collected in a direction orthogonal to the plane of the waveguide to provide information regarding the polarization state of the light propagating in the waveguide. From this data a threshold value of power necessary to initiate the polarization rotation is obtained and used to calculate a value of β15, an asymmetric component of the photovoltaic tensor. The value of β15 for an X‐cut, Y‐propagating channel waveguide was found to be 8×10−13 A/W and that for a rapid thermally annealed Z‐cut, Y‐propagating sample 4×10−14 A/W.

A novel technique, photon scanning microscopy, is shown to probe directly the evanescent field outside a planar and a channel waveguide. The decay lengths for these evanescent fields were measured and correspond well to the decay lengths of the evanescent fields calculated for each structure. Two‐dimensional scanning at constant intensity or constant height reveals lateral variations in these fields due to topographic changes, index of refraction inhomogeneities, or modal variations within the waveguide.

We acknowledge the financial support of the National Science Foundation through grants DMR-0806700, 0806572, 1105362, 1105121, and ECCS-1100489, and the Australian Research Council.

Photocurrent spectroscopy has been carried out on single CdS nanosheet devices in the metal-semiconductor-metal configuration with both Schottky and Ohmic contacts. Spatial imaging of the photocurrent shows that the photosensitive regions are localized at the reverse biased contact for Schottky type contacts and uniformly distributed throughout the nanosheet for Ohmic contacts. Photocurrent spectra show excitonic resonances at low temperatures corresponding to the A, B, C hole bands. Subband gap pulsed laser excitation reveals two-photon absorption dominated photocurrents consistent with a nonlinear coefficient of β=2 cm/GW for these nanosheet devices.

We use time-resolved photoluminescence spectroscopy and photoluminescence excitation spectroscopy to measure the valence band parameters of hexagonal wurtzite InP nanowires. The A exciton emission and excitation energy is observed at 1.504 eV as expected. Excitation spectra show that the B and C hole bands are 30 and 161 meV above the A hole band. From these measurements, we obtain the crystal field and spin-orbit energies of 52 meV and 139 meV, respectively.

Spatially resolved Raman scattering is used to probe the strain distribution in CdS nanosheets. We observe both significant strains and a significant strain gradient across the nanosheets. The magnitude of the strain suggests that electronic properties of the CdS nanosheets will be influenced as well. Using spatially resolved photoluminescence spectroscopy, we show that the band gap of the nanosheet experiences changes in the energy gap of 20 meV across the width of the nanosheet, which are consistent with our observations of the strain.

The InP nanowires are grown by vapor-liquid-solid growth catalyzed by 20 and 50 nm gold nanoparticles on an InP substrate at 400 C using metal-organic chemical-vapor deposition. The 50 nm nanowires were grown with a V/III ratio of 350, while the 20 nm nanowires were grown at a V/III ratio of 700. 9 Extensive cw and time-resolved PL measurements at low temperatures have shown that the 20 nm wires are predominantly WZ, while the 50 nm nanowires are predominantly ZB, with some twins and stacking faults present as determined by high-resolution transmission electron microscopy imaging. 3,4,9 To obtain individual nano

We study the magnetization dynamics in CdMnTe quantum dots using subwavelength optical microscopy imaging at B=0 T. For continuous laser illumination each dot exhibits strong and unique circular polarization despite completely unpolarized ensemble emission. This implies that after an exciton recombines, the spontaneous ferromagnetic alignment of magnetic impurities persists for over 100 μs, which is a million times longer than in CdMnTe quantum wells. The spin memory effect points toward a qualitatively different picture of magnetization dynamics in the zero-dimensional limit.

We have utilized polarized low temperature photoluminescence (PL) to probe the electronic states and structural symmetries of individual CdS nanosheets. High resolution transmission electron microscopy measurements indicate highly crystalline material with different nanosheets exhibiting significant variations of the direction of the c axis, which are consistent with polarization measurements of PL from single CdS nanosheets. The quality of the nanosheets is reflected in measurements of exciton lifetimes of ∼200ps, a value significantly longer than observed for CdS nanowires whose diameter is the same as the thickness of these nanosheets, but shorter than that observed in bulk crystals.

We have utilized spatially resolved low temperature photoluminescence to probe the electronic states and structural symmetries of individual single crystalline CdS nanosheets. Spatially resolved photoluminescence imaging of a single CdS nanosheet reveals a distinctive spectral variation across the nanosheet. We observe A-like exciton states which emit most strongly near the outer edges of the 5μm wide nanosheet, while B-like exciton states emit most strongly along the center region of the 30μm long axis of the nanosheet.

We use polarization-resolved and temperature-dependent photoluminescence of single zincblende (ZB) (cubic) and wurtzite (WZ) (hexagonal) InP nanowires to probe differences in selection rules and bandgaps between these two semiconductor nanostructures. The WZ nanowires exhibit a bandgap 80 meV higher in energy than the ZB nanowires. The temperature dependence of the PL is similar but not identical for the WZ and ZB nanowires. We find that ZB nanowires exhibit strong polarization parallel to the nanowire axis, while the WZ nanowires exhibit polarized emission perpendicular to the nanowire axis. This behavior is interpreted in terms of the different selection rules for WZ and ZB crystal structures. © 2007 American Institute of Physics.

Resonant Raman scattering (RRS) was used to probe the electronic states of CdS nanowires (∼10nm diameter) grown by chemical vapor deposition. Individual Ar+ laser lines were used to vary the excitation energy while observing scattering from CdS phonons; strong 1-longitudinal optical (LO) and 2-LO Raman resonances were readily observed within the broader photoluminescence emission. The energy separation between the peaks of the 1-LO and 2-LO resonance was found to be 34 meV, in good agreement with bulk values. These results demonstrate that RRS is a powerful tool for probing the electronic and vibrational properties of semiconductor nanowires.

Resonant Raman scattering is a sensitive means to probe electronic states in semiconductor materials even when such states are not accessible either through photoluminescence or transport techniques. We show that resonant Raman scattering can be used to probe the excited state distribution of CdTe∕ZnTe quantum dots at room temperature. In particular we apply this technique to study the changes of such quantum dots after rapid thermal annealing.

We report resonant photoluminescence from CdSe/ZnSe self-assembled quantum dots. When CdSe quantum dots are resonantly excited, excitonic sharp micro-photoluminescence peaks originating from individual quantum dots are strongly enhanced in the region corresponding to optical phonon energies below the excitation. The phonons active in this process are identified as the longitudinal optical (LO) phonons from the CdSe dots, as the interface phonons, and tentatively as the LO phonons from the two-dimensional-like precursor layers. These observations suggest that exciton recombination via phonons is a major relaxation process under resonant excitation.

Successful operation of an integrated optical distributed‐feedback (DFB) dye laser in which generated light is confined in a V‐groove optical channel waveguide is reported. Both the channel waveguide and second‐order diffraction grating for DFB operation are formed by anisotropic‐etching the silicon substrate. Polyurethane doped with rhodamine 110 dye is used for the laser waveguide region, while undoped polyurethane is used for channel waveguides. Use of an argon laser for pumping yields continuous output at λ=6430 A characterized by a very low threshold and a spectral width less than 2 A. The output wavelength is consistent with the grating period of 4150 A.

We report successful laser annealing of ZnO optical waveguides deposited on an amorphous SiO2 layer thermally grown on Si. A significant improvement in the optical attenuation of the fundamental mode from several dB/cm before laser annealing to as low as 0.01 dB/cm after laser annealing is observed. Scattering loss measurements for the m = 1 and m = 2 mode are also reported. We attribute the reduction in loss primarily to an improvement in the quality of the ZnO film in the region near the ZnO‐SiO2 interface.

Laser annealing with a CO2 laser is utilized to improve the quality of Corning 7059 glass thin‐film optical waveguides. The 1.0‐μm‐thick 7059 glass film is deposited by sputtering onto a thermally oxidized silicon substrate. Measurement of the absorption coefficient of 7059 glass at λ = 10.6 μm yields a value of 1.12 x 104 cm−1. Dark‐field photomicrographs taken before and after laser annealing imply that both surface defects and bulk inhomogeneities are removed by laser annealing. Waveguide attenuation is measured to be 17.4 dB/cm befor laser annealing and 0.6 dB/cm afterwards.

This letter describes the first optical waveguides fabricated by thermal nitridation of SiO2. This process has allowed us to create layers of silicon oxynitride of about 100‐nm thickness in 4.8‐μm‐thick silicon dioxide layers by exposing thermally oxidized silicon wafers to an ammonia atmosphere for times ranging from one to ten days. Ellipsometric measurements show that the refractive indices of the nitrided layers range from 1.67 to 1.75. Losses for nine optical waveguide samples fabricated with this process range from 0.06 to 0.31 dB/cm.

Integrated detection of light propagating in an optical waveguide with a photodetector array fabricated directly on the waveguide surface is demonstrated. Laser recrystallization of polycrystalline silicon is utilized. Periodically spaced antireflection stripes are used to confine grain boundaries formed during laser recrystallization to the area under these stripes, with photodetector elements formed on single crystal grains between the stripes. Regions containing the grain boundaries are then removed by plasma etching. Lateral p‐i‐n photodiode elements formed by ion implantation are characterized by reverse leakage currents

Rapid thermally annealed silicon‐implanted x‐cut α‐quartz samples have been examined by Rutherford backscattering and Raman microprobe spectroscopy. The data indicate that the silicon has diffused at 1200 °C to form a buried layer of crystallites of size 1–10 μm. The crystallites are preferentially oriented and under substantial stress.

Planar graded‐index SiO2 optical waveguides characterized by very low scattering have been fabricated on silicon substrates by thermal oxidation. Three samples having thicknesses on the order of 15 μm are characterized by waveguide losses less than 1 dB/cm. The appearance of the waveguide streak and out‐of‐plane scattering measurements using photon counting indicate extremely low scattering. The low scattering along with the weak field confinement present in the graded‐index waveguides is consistent with the dominant waveguide loss being due to coupling to the silicon substrate.