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Recently, Fickenscher et al. [1] have shown that, in a core-multi-shell structure where a GaAs quantum well is embedded into an AlGaAs shell wrapped around a [111] oriented GaAs nanowire, the electron and hole ground states are strongly confined to the corners of the hexagonally symmetric quantum well. Thus this confinement defines quantum wires which run along the length of the nanowires along its corners. Here we review single nanowire photoluminescence measurements which show the significant confinement energy of the excitons. For well widths larger than 5 nm, optical transitions between electron and hole excited states can be seen in excitation spectra, while for widths less than 5 nm only the ground state optical transitions are observed. For well widths smaller than 5 nm, high resolution spatially resolved photoluminescence measurements show directly the appearance of localized states. Single nanowire spectra from the 4 nm QWT sample display ultranarrow emission lines on the high energy side of the luminescence band. Spatially-resolved PL images show that these quantum dots are localized randomly along the length of the wire.

We use Raman scattering to study the spatially-resolved strain and stress in a complex zinc blende GaAs/GaP heterostructured nanowire which contains both axial and radial interfaces. The nanowires are grown by metal-organic chemical vapor deposition in the [111] direction with Au nano particles as catalysts, High spatial resolution Raman scans along the nanowires show the GaAs/GaP interface is clearly identifiable. We interpret the phonon energy shifts in each material as one approaches the interface.

We study the photocurrent from photoexcited charged carriers excited with lasers of energy both above and below the energy gap in CdS nanostructures. We observe non-linear photocurrents in CdS nanosheet devices in the metal-semiconductor-metal configuration with Schottky contacts for sub-band gap excitations. Analysis of two-photon absorption dominated photocurrents reveals a nonlinear coefficient of β = 2 cm/GW for these nanosheet devices, which is comparable to those of bulk CdS. We demonstrate the use of the photocurrent polarization measurements to determine the orientation of atoms in the nanosheet.

We demonstrate the newly developed technique Photomodulated Rayleigh Scattering spectroscopy in order to probe the electronic band structure of single semiconductor nanowires. We show that both the electronic transition energies and nanowire diameter can be measured simultaneously and with high accuracy in a single non-destructive measurement. We demonstrate our results for zincblende GaAs as well as wurtzite InP nanowires where we probed the band gaps and transition energies at both room and low temperatures. This technique should advance the study of optical properties of single nanowires as well as other types of nanostructures.

Photoelastic waveguides in bulk Si and SiGe/Si heterostructures have been modelled and characterised. The calculated transverse strain profiles of photoelastic waveguide structures in SiGe/Si heterostructures and bulk silicon are in good agreement with those obtained by microRaman experiments. The waveguide characteristics are also found to be in good agreement with those obtained from the strain modelling and demonstrate that low loss waveguides can be fabricated using these structures

Compositional interdiffusion in Al0.3 Ga0.7 As/GaAs superlattices induced by Si focused ion beam implantation and subsequent rapid thermal annealing is modeled using a set of diffusion equations which take into account the dynamics of the vacancy spatial profile. The inclusion of a new phenomenological term, which depends on the time derivative of the vacancy concentration spatial profile, provides good agreeement with experiment.

Raman scattering experiments on high quality ZnGeP2 single crystals grown by the seeded horizontal dynamic gradient technique have been carried out. Polarized Raman spectra were obtained in the backscattering geometry at both room and low temperatures for several crystal orientations and compared with group theoretical predictions. Raman spectra from as-grown and annealed samples display distinctive differences which were explored by utilizing two different excitation wavelengths: 514.3 nm and 632.8 nm; the observed differences are attributed to a surface interdiffuasion effect.

Compositional interdiffusion in Al0.3Ga0.7As/GaAs superlattice structures with equal 3.5 nm barrier and well widths induced by Si focused ion beam implantation and subsequent rapid thermal annealing has been modeled. A strong depth dependence of the mixing process is observed at a Si++ energy of 100 keV and at a dose of 1×1014 cm−2; this depth dependence is modeled by considering the second derivative of the vacancy profile. That is the maximum in the vacancy injection generated by the transient vacancy concentration gradient. We have included the dynamics of the spatial vacancy profile in the model and find good agreement with experimental results.Interdiffusion across the well/barrier interfaces modifies the subband structure in AlGaAs/GaAs single quantum well (QW) structures. We have investigated the interrelated changes in both confinement energy of the subband states and the composition dependence of the bandgap energy in the QW, both of which are a strong function of the initial well width. Higher order transitions are found to be more sensitive than the ground state transitions to interdiffusion especially during the early stages of interdiffusion. These calculations model the experimental measurements (photoluminescence and photoreflectance) which are used to characterize interdiffused QW structures.

The inelastic light scattering spectra of chalcopyrite structure ZnGeP2 crystals grown by an improved low temperature crystallization from the nonstoichiometric solution of this compound in the liquid Bi or liquid Tl solutions as well as grown by high temperature Bridgman technique has been investigated together with the optical absorption and electron transport measurements.

The effects of interdiffusion on the band structure of two MxGaUxAs/GaAs single quantum well (SQW) structures were studied using room temperature photoreflectance. Rapid thermal annealing of the SQW structures at temperatures of 800°C, 900°C and 1000°C for times up to 180 seconds resulted in limited interdiffusion. Low dose (1014 cm”2) oxygen implantation reduced the thermal stability of these structures where the extent of the interdiffusion was found to be greater for the implanted samples for identical annealing conditions.

Photon scanning tunneling microscopy (PSTM) has been used to obtain effective refractive indices of optical channel waveguide structures. The local evanescent field intensity associated with the propagation modes of optical channel waveguides are measured at two different wavelengths. Both a tapered optical fiber tip and a semiconductor heterostructure tip are employed for detection. Local values of effective refractive index are measured for both TE and TM polarizations and compared to model calculations.

Raman and photoluminescence (PL) spectra have been used to characterize A10.3Ga0.7As/GaAs multiple quantum well (MQW) structures that have been patterned by focused ion beam (FIB) implantation followed by rapid thermal annealing (RTA). Microprobe Raman scattering is used to identify the appropriate RTA and FIB implantation conditions that provide for removal of implantation-induced damage and for compositional intermixing. FIB patterned wire-like structures are characterized by spatially resolved PL spectra.

Raman scattering has been used to characterize ultrathin films of β-SiC, ranging in thickness from 38 nm to 240 nm. These films were prepared on the surface of a Si substrate by a carbonization process at a temperature of 1300°C. In each case, the LO phonon near 970 cm−1 and the TO phonon near 795 cm−1 are observed, indicating the formation of β-SiC crystal. The Raman linewidths and peak positions indicate evidence of nonuniform stress and disorder. The Raman intensity of the TO phonon is nearly twice the intensity of the LO phonon measured both with and without the Si substrate, which indicates that the crystal growth was not entirely confined in the direction.

Temporally and spatially resolved photoluminescence has been used to study patterned structures prepared by focused ion beam (FIB) implantation of multiple quantum wells (MQWs) followed by rapid thermal annealing (RTA). Exciton lifetimes at different positions across the interface between implanted and unimplanted regions suggest that the interface between these two regions is of good quality. Anisotropic exciton diffusion is also observed, suggesting that these structures provide lateral confinement for excitons.

Raman and both cw and time-resolved photoluminescence (PL) spectroscopy have been used to characterize 3.5nm/3.5nm Alo.30Gao.70As/GaAs multiple quantum well structures that have been patterned by focused ion beam (FIB) implantation followed by rapid thermal annealing (RTA). Raman scattering is used to characterize a FIB-delineated optical waveguide structure by identifying the appropriate RTA conditions that provide for removal of ion implantation induced damage in order to produce compostionally mixed regions that possess crystalline order. Spatially and temporally resolved PL spectra provide information on the degree of compositional mixing, exciton lifetime, and lateral transport. Anisotropic diffusion of excitons is observed in samples patterned with parallel line structures.

Optical channel waveguiding in AlGaAs multiple quantum well structures formed by compositional mixing implemented by focused ion beam (FIB) implantation is demonstrated. To achieve selective mixing, Si is FIB implanted with a dose of 5×1014 cm−2 followed by RTA at 950°C for 10 s. Raman microprobe spectra are used to characterize the lateral variation of mixing. Propagation loss in a channel waveguide is measured. Measurement of the waveguide mode field distribution allows for the determination of changes in refractive index due to mixing and an approximate mixing depth.

Results are presented on the fabrication of optical gratings on an Al0.3Ga0.7As/GaAs superlattice (SL) with equal 3.5 nm barrier and well widths, by using locally FIB-enhanced mixing. As the first step, the mechanism of the mixing was studied. Si++ was accelerated to 50 kV and lOOkV and implanted at doses ranging from 1013 to 1015/cm2. A rapid thermal anneal of 10 s at 950°C was utilized. The average Al inter-diffusion coefficient and length were calculated as a function of FIB dose from SIMS depth profiling. The mixing was significantly enhanced by the FIB implantation. The ion dose as low as l×1014/cm2 followed by RTA yields a mixing parameter of ∼90% and results in a two-order of magnitude increase in the diffusion coefficient, to a value of 4.5×10−14cm2/sec, in contrast to 1.3×10−16cm2/sec from RTA-only. The maximum mixing occurred in the region where neither Si ions nor vacancies have their maximum concentration. Instead, it coincides with the location of the positive maximum of the second derivative of the vacancy concentration profile. This fact suggests that in the time frame of RTA and with low dose, the diffusion of nonequilibrium point defects plays a major role in the process of enhancing Al-Ga interdiffusion. DBR optical gratings, consisting of thousands of spacing lines with 350nm period, were fabricated with a lOOkV FIB dose of 2×1013 andl×1014/cm2. Photoluminescence (PL) spectra were taken from the grating region as well as the unimplanted superlattice region. The PL intensity from cavity region of the DBR was about 16 times higher than that from the original SL. This PL enhancement was verified to occur in the cavity region only by spatially scanning over the entire sample. A possible mechanism for this PL enhancement is optical feedback provided by the gratings.

Recent results from our laboratory on the characterization of optical waveguides are reviewed. In particular, two means of experimental characterization that provide spatially local information are presented. Raman microprobe spectroscopy is used to explore the role of stress in a GaAlAs channel waveguide and to characterize the nature of impurity induced compositional mixing in a multiple quantum well structure suitable for optical waveguiding. Finally, photon tunneling microscopy is shown to probe the optical waveguide evanescent field and thus the local surface and index variations in an optical waveguide.

Low temperature photoluminescence spectra have been used to characterize conventional ion beam (CIB) and focused ion beam (FIB) implanted superlattices. The excitation dependence of the single scan FIB is found to be significantly different from CIB and multiple scan FIB implantations which are similar. The peak position of the donor-acceptor transition is observed to change to higher energies significantly slower with excitation intensity for the single scan FIB case when compared to the multiple scan FIB and CIB cases. Simple models to describe these effects are briefly discussed.

Results are presented on FIB mixing of an Al0.3Ga0.7As/GaAs superlattice with equal 3.5 nm barrier and well widths. Si++ was accelerated to 100 kV and implanted parallel to sample normal at doses ranging from 1013 to 1015/cm2. The level of inter-layer disordering was measured primarily by Auger depth profiling. The mixing effect of RTA-only increased roughly linearly with annealing time at both 950 and 1000°C, with the latter exhibiting a sharper slope. At either temperature, 90 s was sufficient to produce complete mixing within the accuracy of the measurement. An anneal of 10 s at 950°C, which was utilized in subsequent post-implantation annealing, resulted in ∼ 25% thermally-induced mixing, with a corresponding PL “blue shift” of 6 meV. The level of mixing by an ion dose of 1 × 1014/cm2 yielded a mixing parameter of 0.87, where 1.0 represents complete mixing. This is the lowest ion beam dose necessary for nearly complete mixing reported to date for either FIB or BB implantation. Doubling the dose to 2 × 1014/cm2 results in an increase in mixing by only 0.05 to 0.92. Larger doses produced a diminishing increase in mixing parameter.

Raman scattering has been used to characterize lattice damage and impurity-induced compositional disordering in AlGaAs superlattice suitable for optical waveguiding. The degree of damage induced by both conventional ion beam (CIB) implantation and focused ion beam (FIB) implantation is studied using a spatial correlation model to interpret the Raman spectra. FIB implantation is found to induce slightly more damage than CIB implantation for doses of 8×1013 cm−2 and 4×1014 cm−2. and significantly more damage with 2×1015 cm2 compared to CIB implantations of the same dose. Suitable FIB implantation and rapid thermal annealing (RTA) conditions which provide compositional mixing were determined using Raman and photoluminescence spectroscopy. Using these conditions, an optical channel waveguide in AlGaAs superlattice formed by FIB-induced compositional intermixing is demonstrated.

Diamond films have been synthesized by microwave Plasma Enhanced CVD (PECVD) and permanent magnet induced Electron Cyclotron Resonance (ECR) PECVD of hydrogen diluted methane. The films are characterized by SEM images and Raman spectroscopy. The diamond films grown by ECR-PECVD show clear-cut habits of cubic crystal in SEM images, while the film grown by microwave PECVD are the polycrystalline. A Raman line at 1333cm‒1 and broad band located at ∼1500 cm‒1 were obtained for the films grown by both methods. However, the film grown by microwave PECVD shows a larger broad band which is associated with an sp2-bonded graphitic phase

Integrated detection of light propagating in an optical waveguide by a photodetector array fabricated directly on the waveguide surface is demonstrated. Laser recrystallization of LPCVD polysilicon patterned with periodically-spaced anti-reflection stripes is utilized. Lateral p-i-n photodiode elements formed by ion implantation are characterized by reverse leakage currents of < 10−11 amp and a typical breakdown voltage of 50 volts. Optical response is found to be linear over a dynamic range of greater than 55 dB.

Optical channel waveguiding has been observed in a structure consisting of a silicon nitride ridge on a multilayer GaAlAs heterostructure. The silicon nitride layer was deposited and then patterned to form 3.5 micron wide ridges. The optical field intensity radiating from the endface of the channel waveguide is found to have two peaks symmetric about the center of the silicon nitride ridge. Raman microprobe spectroscopy indicates a significant stress-induced shift in the GaAs longitudinal phonon frequency. Rapid thermal annealing reduces the stress and changes the optical field intensity distribution to a single symmetric peak.

Rapid thermal annealing has been used to initiate diffusion of Ti in LiNbO3 for the fabrication of optical waveguides. The sample with the most rapid initial ramp of temperature to 875 C was found to have the lowest propagation loss of 1 dB/cm. In order to more fully understand these channel waveguides, we have utilized Raman microprobe spectroscopy. Preliminary results suggest that the presence of the Ti in the LiNbO3 lattice dramatically alters the Raman response.

Laser recrystallization of silicon on an insulating substrate has been carried out by irradiating polysilicon with both an Ar+ laser operating on all lines in the visible and a CO2 laser operating at 10.6 microns. These experiments were carried out over a variety of laser power densities and substrate temperatures. The use of the two lasers allowed for independent spatial control of temperature in both the polysilicon and the SiO2 layers and helped to reduce the strain at the polysilicon - SiO2 interface. We report the successful recrystallization of polysilicon films without substrate heating for two different silicon-on-insulator structures.

Raman Scattering as a technique for studying the formation of tungsten silicide is presented. The tungsten silicide films were formed by rapid thermally annealing tungsten films that were sputter deposited on silicon substrates. The Raman scattering data is correlated with data from resistivity measurements, Auger and Rutherford Backscattering measurements, and scanning electron microscopy.