We report in this paper results from photoluminescence studies on InP/AlInAs/InP double heterostructure. We particuliary focus on the 1.26 eV recombination (also refered as the 1.3 eV transition) that originates from the inverse interface. We will show that its optical properties is related to the non commutativity of the AlInAs/InP band offset.

We have studied the transient behaviour of a sharp emission line, which emerges close to the heavy-hole (hh) exciton photoluminescence line in a 1.6 monolayer thick InAs layer embedded in a GaAs matrix, when the light-hole (lh) exciton transition is excited. We find, that the decaytime of the sharp line is equal to the lh-exciton lifetime for excitation on resonance, but it strongly decreases for excitation off resonance. Since in our structure the energy separation between the hhand lh-exciton transitions amount to one GaAs LO phonon we conclude, that the sharp line originates from double resonant Raman scattering for off resonant excitation, whereas it is predominantly due to resonant luminescence for excitation on resonance. The strong decrease of the intensity of the sharp line due to a temperature rise from 4 to 18K proves the existence of a well confined lh-exciton state. In addition, we performed carrier capture measurements on this structure. We find a constant capture time of 20ps at the lh-exciton transition, whereas the capture time decreases step-like from 55ps to 22ps within the hh-exciton transition. This provides clear evidence for a two-step capture process, where the lh-level acts as an intermediate capture state.

Three dimensional lattices of semiconductor nanostructures were prepared using porous artificial opals as templates. Opals are natural gratings for visible light, and the template forces the semiconductor to follow the size (typically 100 nm) and symmetry (fcc) of their void-like lattice. The purpose of using this material is to match the wavelength of the emitted light from the semiconductor component with one of the lattice's own modes to enhance the luminescence efficiency. TiO2 was grown using in-cavity, multiple step synthesis by CVD. The band gap of the composite is near 3 eV. Raman scattering, absorption and photoluminescence (PL) spectra were examined for various amounts of TiO2 in opal. Transmission of the PL through the composite shows an intensity decrease at 2.15 eV which is not in the region of interband absorption of composite components. This corresponds to the structure possessing an overall refractive index between that of opal (1.45) and rutile (2.3) of 1.8.

PL and PR measurements have been performed on a set of silicon samples p-type doped between 1018 cm−3 and 1020 cm−3. Both optical methods are shown to be complementary as the bandgap narrowing effect is clearly evidenced from PL results, whereas low temperature PR results rather show the filling effect of the valence band, in good agreement with theoretical determinations. We observe an increase of E′0 transition as p-type doping level is increased.

PR spectra of Si and SiGe alloys at low temperature are presented together with theoretical fitting using the third derivative functional form of the unperturbed dielectric function of both direct optical transitions involved in the main PR feature : E′0 and E1.

This characterisation work will be discussed by pointing out that PL and PR results are closely connected, allowing the measurement of the effect of heavy doping on the Si and SiGe band structures.This study is fully relevant to high speed bipolar transistor development.

The effects of the channel electron density on the interband optical transitions of strained (x = 0.6 and 0.65) and lattice-matched (x = 0.53) lnxGa1−xAs/In0.52Al0.48As/InP high electron mobility transistor structures have been investigated by phototransmittance at room temperature. Analysis of the ground and first excited transitions for low and high densities, respectively, enabled a separate estimation of the electron densities occupying each one of the first two subbands. It was found necessary to include the modulation of the phase-space filling in the analysis of the spectra, especially for the samples with a high electron density, in which case this mechanism becomes dominant.

The fabrication of GaAs-GaAIAs coupled quantum dots and of quantum rings using electron beam lithography and dry etching is described. Coupled dots of physical diameter of 500 and 250 nm were fabricated and processed with top electrical contacts to apply an electric field. We show that the emission spectrum of coupled dots is modified by the electric field. Quantum rings of 400 nm outer diameter and wall thickness of 25 nm were fabricated. The emission spectrum from rings showed the quantum well emission shifted to higher energies and although its intensity decreased by about one order of magnitude there was little linewidth broadening.

This work introduces a new interference technique for the diagnostic characterization of hydrogenated silicon thin films. The interference technique is based on new self-consistent data analysis algorithms for simultaneous optical transmission and specular reflection using exact interference equations for the system of a film on a substrate. It provides a quick non-destructive optical measurement of absorption coefficient and refractive index spectra of amorphous silicon (a-Si:H) and polycrystalline silicon (poly-Si:H) thin films in a wide range of the incident photon energies (0.5–3.5 eV). This non-contacting, high sensitivity method is a powerful probe of various material properties including thickness, refractive index and absorption spectra, hydrogen content, alloy fraction, energies of localized defect states and their concentrations. Experimental results for optical study of hydrogenated Si films indicate that the proposed method makes possible high precision measurements of the absorption in the region near the fundamental edge. In this region the absorption coefficient varies over several orders of magnitude. Also, the absorption related to impurities and defects in the subgap energy region at least from 102 cm−1 can be detected. As a result, the interference technique shows promise in providing feedback for monitoring film growth and device fabrication processes.

Using a photoelastic modulator in the optical-bridge configuration, the reflectivity difference was obtained for GaAs and ZnSe (100) surfaces over the photon energy range from 1.5 eV to 6 eV with various azimuthal orientations of the surface. The RD data of GaAs (100) are similar to previously reported data. The RD data of ZnSe (100) are larger by an order of magnitude than those of GaAs (100), possibly due to the larger ionicity of Zn and Se atoms. The distinctive critical point structures and interference patterns shown in the RD spectra of ZnSe (100) suggest that the data, if obtained in real time, could be used to determine the alloy composition, thickness and temperature during growth. The RD data are analyzed using models proposed by Aspnes. The results indicate that the major contribution to the RD spectra of ZnSe (100) are from the surface local field unlike the RD spectra of GaAs (110), whose major contribution is from the bulk spatial distribution.

A Photoreflectance (PR), Photoluminescence (PL), Raman scattering and Ellipsometry optical characterisation study of He and SiCl4 reactive ion etched 1018cm−3 n-type GaAs is presented. Ellipsometric and PL data reveal significant modifications to the GaAs substrates for the He plasma as a function of etch power and etch gas pressure. Raman data reveal an increase in the depletion depth while the surface electric field data, extracted from PR spectra, decrease with etch severity. This is accounted for by a plasma etch induced decrease in the near surface net carrier density. Ellipsometric and PL measurements of SiCl4 etching reveal evidence of an improvement in the GaAs surface crystallinity while PR and Raman data are consistent with an increase in the surface carrier concentration. Optical characterisation data are correlated with electrical measurements using capacitance-voltage profiling.

We have performed low temperature photoreflectance spectra on several MBE-InAlAs layers lattice matched to InP. Unusual lineshapes of PR spectra are observed at temperatures below 40K, characterized by a step at the InAlAs band gap energy. This step is shown to be related to a strong modification of the photo luminescence background of the photoreflectance spectra. This modification is attributed to an effect of carrier localization due to clustering effects in the InAlAs layers

In this paper we introduce a real-time optical probe technique, p-polarized reflectance spectroscopy (PRS), for the monitoring of epitaxial growth processes. GaP heteroepitaxy by pulsed chemical beam epitaxy (PCBE) is used as an example. PRS allows to follow the deposition process with submonolayer resolution, utilizing a fine structure that is superimposed to the interference oscillations in the reflected intensity. This fine structure is explained by the periodic alteration of the surface reaction chemistry under pulsed chemical precursor supply. In the case of epitaxial GaP growth, it is modeled for a four layer stack, including an ultra-thin surface reaction layer of periodically changing thickness do(t) and dielectric function εo(t) tied to the periodic surface exposure to tertiarybutyl phosphine (TBP) and triethylgallium (TEG) pulses, respectively. The imaginary part of the dielectric function, εO2, of this surface reaction layer can be determined directly from the distance of the inflection points in the fine structure, where the optical response to the first precursor pulse in the cycle sequence changes sign, from the closests interference minimum. The surface reaction kinetics can be studied by analyzing the decay time characteristic in the transients of the fine structure.

We have demonstrated real-time feedback control of thickness and composition for Bragg reflector structures using in situ multi-wavelength ellipsometry. This demonstration was performed under conditions which were not ideal for ellipsometric measurements: the angle of incidence for the ellipsometric measurement beam was far away from the Brewster angle, substrate rotation was enabled (which caused an angular wobble in the measurement beam), and strain effects were present in the ellipsometer windows. Furthermore, to simulate drift in the MBE system (and test the effectiveness of the ellipsometer control), the Ga effusion cell was ramped to change the Ga flux by 50% during two of the growth runs. Results of the growth control precision and accuracy are presented; the influence of the non-ideal measurement conditions on the ellipsometer growth control capability is also discussed.

The morphology, chemical state and oxidation behaviour of electroless copper films deposited from two different baths were characterised using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS) and spectroscopic ellipsometry (SE). The electroless solutions used were a commercial electroless formaldehyde (HCHO)-based solution (Cupro-Thick 84, Alfachimici) and an electroless solution developed within the NMRC which was based on dimethylamine borane (DMAB). Both methods produced as-deposited copper films with different morphologies. SE analysis of the as-deposited films and those oxidised in a dry synthetic air environment between 75°C–150°C indicated that the freshly deposited films had inherent oxide layers of between 45Å–92Å and that significant growth of these only occurred at temperatures above 100°C within 180 minutes isothermal oxidation periods. XRD analysis confirmed that the oxidation products formed were a mixture of cuprous oxide (Cu2O) and cupric oxide (CuO). Multiple linear regression analysis of the rates of change in oxide layer thicknesses as a function of both time and temperature indicated that mixed rate laws dominated. The application of an oxidation inhibitor was shown to prevent oxidation of the asdeposited commercial copper films when heat treated at 125°C.

The use of spectroscopic ellipsometry (SE) to characterise the effects of rapid thermal annealing on Si implanted with phosphorous and phosphorous with fluorine are presented. Variations in the measured SE spectra with anneal temperature and presence/absence of fluorine are clearly observed. Spectra are successfully modelled using refractive indices which are graded with depth. Comparison with cross-sectional transmission-electron microscopy and secondary ion mass spectroscopy show that the results can be correlated with both the crystallinity and impurity distribution in the poly-Si.

The room temperature electrical characteristics of AlAs/InGaAs/InAs resonant-tunneling diode (RTD) devices are sensitive to sub-monolayer thickness changes, and present a challenging case for closed-loop control. We prepared stacked RTD structures by MBE in which the strained AlAs barrier thicknesses were controlled based on an in situ spectroscopic ellipsometry (SE) system. The short-term and long-term reproducibility of RTDs grown under SE-based control was compared with similar samples grown by “dead-reckoning” (timing-based shutter openings coupled with pre-growth flux calibrations). SE-based calibration can compensate for long-term flux drift, but closed-loop thickness control did not provide a significant improvement over deadreckoning in terms of short-term RTD reproducibility.

We report surface-induced optical anisotropy (SIOA) spectra and dielectric function data of vicinal Si(001) surfaces using reflectance-difference spectroscopy (RDS) and spectroscopic ellipsometry (SE). To find the main contributions of the optical response we took data for clean and by hydrogen, oxygen, and arsenic modified surfaces. The SIOA lineshapes, as measured by reflectance-difference (RD) spectroscopy, can be either derivative-like or similar to the dielectric function as measured by SE. The derivative-like spectra appear to be associated with step contributions while the dielectric-function-like behavior appears to arise from terrace dimers and/or changes in chemical species bonded to the steps. In addition, we present SE data of silicon nanostructures formed by electrochemical etching and find that their behavior is dominated by interface properties.

The dielectric functions of 0.5–1.5 μm Znl-xCdxSe (0≤x≤0.34) epilayers on GaAs have been determined over the photon energy range 1.5≤E≤5.3 eV. These spectra have been parameterized using the Sellmeier approximation for energies less than the fundamental gap at E0 and using a sum of Lorentz oscillators above the gap region. As an example of the usefulness of the approach, expressions are provided that yield the index of refraction of Znl-xCdxSe (0≤x≤ 0.34) for 1.5 eV≤E<E0- As a second example, we have determined the composition and thickness of a Znl-xCdxSe quantum well between ZnSe barrier layers.

Spectroscopic ellipsometry was used to characterize several short-period SimGen strained superlattices grown on Si(100) substrates or on graded SixGel-x alloy buffers (strainsymmetrization) by magnetron sputter epitaxy, a novel technique with potential application to industry-scale production of epitaxial Si/Ge heterostructures. Ellipsometric spectra were analyzed within a multilayer model, which included an oxide overlayer, in order to derive the effective dielectric fimctions of the SLs. spectra cannot be simulated by a sequence of Ge+Si slabs and compared to those of the compositionally equivalent alloys showed noticeable differences which can be ascribed to a combination of strain and confinement effects. The results agree with experimental findings and theoretical predictions on analogous SLs grown by MBE, thus confirming the reliability of the used technique to produce good quality SLs.

Spectroscopic ellipsometry from 1.4 to 5 eV was used to systematically characterize epitaxial heterostructures AlxGa1-xSb/GaSb for different x concentrations (x≤0.5). The structures were grown by MBE at temperatures and beam equivalent pressure ratios which optimize their lowtemperature photoluminescence properties. Complex dielectric functions of AlxGa1-xSb versus x were derived, for the first time, from the ellipsometric spectra after mathematically removing the oxide overlayer effects. The spectra were analyzed with their second energyderivatives in term of standard analytical lineshapes: in particular the El, E1+Δ1 and E2 critical point energies, broadening and amplitude parameters were derived as a function of x. On this basis we verified that the energy-shift model is appropriate to interpolate for any x≤0.5, thus allowing a nondestructive optical diagnostic of layer thickness and composition of epitaxial heterostructures based on A1xGa1-xSb.

SIMS is a well-established technique for the measurement of impurities in semiconductor materials. It is the technique of choice for the measurement of very low levels of impurities, especially depth profiles. Accelerator Mass Spectrometry (AMS) is also a well-established technique and is primarily used for measurements of abundance ratios of long-lived radionuclides, such as 14C and 36C1 to their respective stable isotopes. A combination of these techniques holds the potential for impurity determination in semiconductors at the ppt level. The new technique, Trace- Element Accelerator Mass Spectrometry (TEAMS), eliminates the problem of molecular interference which is the major constraint limiting the sensitivity of SIMS. Depth profiles for B, P and As implants in Si, obtained by TEAMS are presented below.