Table of contents

Synchrotron x-ray topography was used to evaluate dislocation generation for liquid phase heteroepitaxy of strained layer on n-type InAs substrates. Severe misfit dislocation generation is observed for epilayer thicknesses of 4 and many of these form threading dislocations which are observed at the surface. However, for thicker epilayer growth (up to 70 in this study), this misfit dislocation generation appears to be confined to a region close to the heterointerface, with few threading dislocations approaching the surface. These data correlates well with photoluminescence and optical microscopy measurements.

The basic idea of the work is that in going from simple semiconductors to more complex chemical compositions one usually deals with nonstoichiometric or intentionally undoped compounds. Combined with other specific features of d(f)-compounds, this may lead to an unusual temperature-dependent impurity contribution to the overall scattering of carriers, together with the contribution from scattering by spin disorder typical of magnetic semiconductors, even in impurity-free semiconductors. Based on a model Hamiltonian, a unified scheme is proposed for calculating the band structure of the lower conduction-band edge of a degenerate ferromagnetic semiconductor and the temperature and field dependences of the impurity contribution to the resistivity of the semiconductor. The calculated magnetoresistance has a sharp maximum at a temperature near . As an illustration, the results of calculation are compared with the corresponding experimental dependences of conductivity in a ternary semiconductor, n-, generally exhibiting no stoichiometry with respect to the chalcogen.

We report a full-scale pseudopotential study of the optical properties of InAs/ and InAs/ superlattices, with particular emphasis on the infrared range of wavelengths. For both structures we examine the detailed origin of the absorption response and how cutoff wavelength varies with the period of the superlattice and with the alloy concentration. This entails a discussion of how wavefunction localization, band mixing and energy band dispersion can affect the absorption coefficient. Particular attention is paid to structures with cutoff wavelength in the ranges 2-5 m and 10-13 m. Calculated absorption spectra are compared with examples obtained experimentally. Although agreement between the spectra is good, it is found that neither the sharp features nor the absolute magnitude is reproduced adequately by the electronic structure obtained from idealized systems. Comparison of the bandgap with the gap between the highest two valence states allows structures where certain Auger recombination processes may be inhibited to be indicated. The effects of alloy scattering in the InAs/ system has also been investigated. A second-order perturbation theory calculation of the linewidth associated with the alloy potential suggests that the effects of alloy scattering are too large to be modelled as a perturbation of the virtual crystal case. A full-scale treatment is required to quantify this effect.

This paper discusses the hydrostatic and shear deformation potentials of ZnSe by investigating cathodoluminescence (CL) spectra of biaxial tensile strained single quantum wells (SQW). The dependence of the shift of light- and heavy-hole exciton lines on the built-in strain of these MBE-grown strained layer heterostructures is discussed. We found a hydrostatic deformation potential of eV and a shear (tetragonal) deformation potential of eV. From the temperature dependence of the ground state exciton energy, an exciton gap meV at T = 297 K was deduced for unstrained bulk ZnSe.

Low-magnetic-field magnetoresistance of a two-dimensional electron gas (2DEG) in a triangular quantum well at a single InAs-InP heterointerface has been studied. It was shown that the spin-orbit relaxation plays a significant role in the low-field magnetoresistivity in a wide range of 2DEG densities (1.8- cm. Analysis shows that both cubic and linear terms in the wavevector must be taken into account in spin splitting to describe experimental results. The linear term is mainly related to the asymmetry of the quantum well (Rashba term). Analysis of the density dependence of the spin-orbit interaction rate permits separation of the spin splittings related to the lack of inversion of the crystal and to the asymmetry of quantum well and determination of the spin splitting parameters for 2D electrons in asymmetric InAs quantum wells.

The deep levels existing in fully ion implanted and rapidly thermally annealed InP junctions were investigated in this work. The samples were co-implanted with magnesium and silicon. An additional phosphorus implantation was carried out in some samples to study its effect. In order to characterize the traps, deep level transient spectroscopy (DLTS) and the capacitance-voltage transient technique (CVTT) were used. For a (control) sample implanted with Mg only, four deep electron levels located at the upper half of the band gap (at 0.45, 0.2 eV 0.25 and 0.27 eV below the conduction band) were detected by DLTS. On the contrary, for the Mg-Si- and Mg-P-Si-implanted samples only two of them (at 0.25 and 0.27 eV below the conduction band) were observed. Several characteristics of each trap were derived by CVTT measurements. Tentative assignments have been proposed for the physical nature of these deep levels.

Slow positron implantation spectroscopy has been applied to the investigation of point defects formed during the synthesis of buried SiGe alloy layers in Si by high-dose implantation and post-amorphization with . It is seen that omitting the post-amorphization stage prior to annealing leaves a damaged layer, containing open volume defects, extending beyond the -implanted overlayer. Provided that the Ge dose is low enough to allow planar crystal regrowth, post-amorphization appears to inhibit defect formation. Samples implanted with higher doses contain as-yet unidentified defects.

The in situ real-time monitoring of the selective etching of semiconductor structures with a Raman microprobe system is demonstrated for the first time. The technique that is applied to GaSb/AlSb/InAs heterostructures allows the accurate timing of the etching as well as a study of the chemistry of the etching process and can be applied to many problems in the processing of compound semiconductors. During etching of AlSb a surface layer rich in Sb builds up that slows down the etch rate, whereas GaSb is etched without producing this residue layer. The different etching behaviour of AlSb and GaSb is confirmed by measurements of the etching depth in patterned samples by means of a Dektak stepper. The origin of the antimony layer is explained.

Thin films of have been deposited by RF magnetron sputtering onto 100 mm diameter n-type single-crystal Si wafers. Full deposition and post-deposition variables have been investigated with respect to their effect on the dielectric constant and refractive index of the thin films. Specifically for use as insulators for thin film electroluminescent (TFEL) devices, the films need to exhibit a high dielectric constant and a low refractive index. The optimum fabrication route was determined to be deposition at C in a 30% in Ar atmosphere at 7 mTorr with a post-deposition anneal at C for 1 h. Demonstrated here is that films exhibiting suitable characteristics, namely, and n = 2.1, for use in TFEL devices can be fabricated using RF magnetron sputter deposition.

ZnTe single crystals grown by the cold travelling heater method have been investigated by means of photo- and cathodoluminescence. The spectral region covered in this work ranges from 2.48 eV (500 nm) which corresponds to band-edge emission to 0.62 eV (2000 nm). Visible and infrared cathodoluminescence images have been recorded, and the influence of extended defects on the observed luminescence has been studied.

Alloy scattering is studied for quantum wires of , , and systems. Electron mobility is also evaluated for different dimensions of these structures for the temperatures of 40, 77 and 300 K. It is found that alloy-scattering-limited mobility is lower than acoustic-phonon-scattering-limited mobility in systems. Even in GaAs systems alloy scattering is significant for wire diameters less than 10 nm.

A substantial improvement in the electrochemical capacitance-voltage (eCV) profiling technique is proposed by effectively reducing the diode area, thereby extending the range of applicability of this technique to highly spatially confined carrier systems and heterostructures. This modified technique makes use of the dielectric properties of photoresist films into which small area holes can be defined by standard photo- lithographic techniques. It is easily implemented in a commercially available system and excellent quality data across silicon (Si)/silicon-germanium (SiGe) two-dimensional electron gas (2DEG) heterostructures and delta- (-) doped gallium arsenide (GaAs) layers are obtained reproducibly. Applying this technique to modulation-doped field-effect transistors (MODFETs) it is possible to clearly identify the supply, spacer and channel layers in such structures; corresponding measured sheet densities exhibit excellent agreement with those determined by other techniques. The proposed modifications raise the eCV technique to a valuable complementary assessment tool in the determination of room temperature transport properties of heterostructures with device layer design.

quantum well structures of high quality were grown by molecular beam epitaxy. The structural and electrical quality was characterized by x-ray diffractometry, Raman spectroscopy and Hall transport measurements. When an optimized buffer layer was used on a GaAs substrate, electron mobilities of at 300 K and at 20 K were routinely achieved for undoped structures. These excellent transport properties were utilized in a sensitive magnetoresistive sensor.

Conjugated polymers are organic semiconducting materials that can emit light. These polymers have the advantages of being light, cheap and easy to process, and in addition the band gap can be tailored. We report the microfabrication of surface light-emitting diodes (SLEDs) on silicon substrates in which the electrodes are underneath the organic electroluminescent layer. Patterned electrodes are separated by a 2500 Å thick insulating layer of silicon oxide or are interdigitated with a separation of 10 or 20 m; the luminescent polymer is spin coated or solvent cast on top of the electrodes. This fabrication method is completely compatible with conventional silicon processing because the polymer is deposited last and the light is emitted from the upper surface of the diodes. Despite the large spacing between electrodes, and despite the absence of an evaporated top contact, the voltages required for light emission were not much greater than those used in conventional sandwich-type structures.

A new method is proposed to produce sheet- or ribbon-like silicon from the melt using a contactless electromagnetic shaping action based on the cold-crucible principle. The ribbon shaping by magnetic repulsion may be limited to a single-side application and used in conjunction with other ribbon growth techniques such as the ribbon growth on substrate method. A growth experiment in a cold crucible resulted in some extrusion of sheet-like shaped silicon in the container openings. This experimental finding supports the view that the proposed ribbon growth technique is indeed feasible.

Because dilute HF solutions (DHF) are most commonly used for wet cleaning of silicon surfaces, an extensive experimental study has been developed to investigate the effect of oxidant additives such as and . The results show that these agents could efficiently prevent contamination of the silicon surface by trace amounts of metal ions. Moreover, electrochemical methods were very sensitive and allowed the detection of ions at a level of a few tens of ppb, even when a sophisticated technique, based on the quantification of the fluorescence signal of metallic elements (TXRF), could not perceive any surface contamination.

The responses of p- and n-type silicon wafers were investigated in DHF solutions containing or and traces of copper ions. Because of the high electron concentration, n-type silicon was very sensitive to cathodic reactions, while p-type silicon was inhibited by the limiting minority carrier current. The electrochemical results were interpreted in terms of reactivity of anodic and cathodic sites, the reduction rate of the oxidizing species, and , being sharply enhanced by the electrocatalytic properties of the first nanometric copper nuclei.

The electrochemical response constitutes a powerful tool for monitoring the wet treatment lines for production of ultra large scale integrated (ULSI) microcircuits.