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This letter presents an experimental study of interface trap parameters versus energy. Our method is based on conductance measurements as a function of angular frequency and temperature G(ω,T). The temperature is swept between 300 and 500 K in order to increase the mid-gap sensitivity. Capacitance as a function of voltage is used to establish the relation between the surface potential and the gate voltage at each temperature value. Then the conductance dispersion as a function of frequency is analysed in order to determine the distribution of the interface states D_it and of their capture cross section σ_n,p. Our results are in good agreement with those published on DLTS measurements. This confirms the capability of this technique compared with emission time spectroscopy, which implies a complex treatment of the measured data. Our G(ω,T) procedure brings an accurate observation of two different populations of traps and we propose a classification of `slow' and `fast' states.

The formation of thermally stable highly resistive regions in n-type GaAs layers during helium ion bombardment at elevated temperatures, where dynamic annealing of radiation-induced defects is substantial, was investigated and presented here. The substrate temperatures were chosen to be room temperature (RT), 100 and 200 °C. Semi-insulating GaAs wafers of (100) orientation were implanted with multi-energy ²⁹Si atoms to create a flat dopant distribution of about 0.7 µm in thickness. A uniform damage density was formed within the conductive layer by 2×10¹⁴ cm^-2 helium implantation at 600 keV to isolate the structure. Resistivity and Hall measurements were performed in order to study the evolution of the sheet resistance and Hall mobility as a function of post implant annealing temperature in these resistors implanted at three different temperatures. The samples were annealed in the range 100-800 °C and an optimum isolation of >10⁷ ohms/□ was achieved for samples implanted at either RT or elevated temperatures after annealing at 400 or 450 °C, respectively. Annealing at higher temperatures returned the resistivity to a value close to that of the starting material and it was found that RT implants recover quicker than elevated temperature implants. The isolated regions exhibited good stability to heat treatment up to 550 or 650 °C for 100 or 200 °C implants, respectively. No such annealing window for the thermal stability of the obtained isolation was found for samples implanted at room temperature. It is believed that isolating defects are more thermally stable in the case of hot implants than those formed by RT implantation.

A method for the passivation of indium phosphide, based on thiolated organic self-assembled monolayers (SAMs) that form highly ordered, close-packed structures on the semiconductor surface, is presented. It is shown that the intensity of steady-state photoluminescence (PL) of n-type InP wafers covered with the thiolated SAMs increases significantly (as much as 14-fold) upon their covering with the monolayers. The ease with which one can tailor the outer functional groups of the SAMs provides a way to connect this new class of passivators with standard encapsulators, such as polyimide. Indeed, the PL intensity of SAM-coated InP wafers was not altered upon their overcoating with polyimide, despite the high curing temperature of the polymer (200 °C).

Using a segmented-contact method, we have measured the optical mode loss in a series of AlGaInP 650 nm large optical cavity laser diodes with cladding layer thicknesses of 1.0, 0.5 and 0.3 µm. For the thinnest cladding layer the loss is 24 cm^-1 greater than the other devices and by comparison with transfer matrix calculations we show that this is due to penetration of the mode into the outer GaAs layers. The results show that the cladding thickness can be reduced to about 0.5 µm without significant increase in loss and threshold current and this could be beneficial in reducing the electrical and thermal resistance of the cladding layer in high power structures.

Electromigration of foreign aluminium atoms, arising from contact pads, along polycrystalline molybdenum silicide (MoSi₂) metallic interconnect lines has been studied. The MoSi₂-lines with aluminium contact pads on both ends were exposed to electric direct current with densities of between 10⁶ and 10⁷ A cm^-2 over 2000 h. While mass transport of constituent atoms of the line material was not observed, the atomic migration of aluminium is clearly directed from the cathode side toward the anode. Characteristic hillocking along the interconnect line is observed. This result is in accord with the action of a partially grain-blocked polycrystalline via due to clusters, which are present along the line. Compressive stress in front of blocking silicide grains is found to induce a positive mass flux through the line surface. Scanning electron microscopy micrographs, and energy-dispersive x-ray analyses are applied to identify the chemical nature of the degradation sites. It is found that aluminium from the cathode pad incorporates into the interconnect and migrates under the action of the electron wind.

We have investigated the photo-excited capacitance-voltage (C-V) characteristics as well as the photoluminescence spectra under different biases of a wide quantum well (QW) embedded in an n⁺-i-n⁺ double-barrier structure. The pronounced peak feature at zero bias in the C-V spectrum observed upon illumination is regarded as a kind of quantum capacitance related to the quantum confined Stark effect, originating from the spatial separation of the photo-generated electron and hole gas in the QW. This fact is further demonstrated through the comparison between the C-V curve with the PL intensity versus applied voltage relationship under the same excitation. The results may provide us with a more direct and sensitive means in the detection of the separation and accumulation of both types of free carriers - electrons and holes - in low-dimensional semiconductor structures, especially in a new type of optical memory cell.

In_0.5Ga_0.5P/In_0.2Ga_0.8As pseudomorphic high electron mobility transistors (PHEMTs) fabricated using single- and dual-gate methodologies have been characterized with special emphasis on precisely controlling the device linearity and the gate-voltage swing. A composite channel employing a GaAs delta-doped (δ(n⁺)) sheet and an undoped In_0.2Ga_0.8As layer characterizes the key features of the proposed PHEMT profile. Better carrier confinement for both the electron and the hole due to the InGaP/InGaAs hetero-interface and superior carrier transport properties at the channel/buffer interface, together with the redistributed carrier profile, contribute to high-linearity performances. On the other hand, high etching selectivity between the GaAs cap and the InGaP Schottky layers makes it possible to precisely position both of the gates. The gate-voltage dependence of transconductance for the first equivalent gate with several V_GS2 shows that the available gate-voltage swing is in the range 0-4.0 V.

A thermodynamic approach to analysis of the growth of InGaAsN compounds by molecular beam epitaxy (MBE) is proposed. The developed thermodynamic model allows estimation of the mole fraction of nitrogen in the obtained alloys as a function of external growth parameters: element fluxes and growth temperature. The model predicts that the nitrogen incorporation is temperature-independent below 500 °C and markedly diminishes at higher growth temperatures. The incorporation of nitrogen is suppressed on raising the arsenic flux; the content of group III elements in the alloy affects the nitrogen incorporation only slightly. The results of simulation are compared with experimental data on MBE-grown InGaAsN alloys with small nitrogen content (<3%).

The optical and structural properties of ion-implanted 6H-SiC single crystals were investigated for samples implanted with 370 keV ²⁸Si ions to doses ranging from 5×10¹³ to 1×10¹⁶ cm^-2 and at irradiation temperatures ranging from 20 to 600 °C. Rutherford backscattering spectrometry channelling (RBS/C) showed that the dynamic recovery of the induced-damage layer increases with irradiation temperature. The final disorder determined from RBS/C as a function of implantation temperature was modelled in terms of a thermally activated process which yielded an activation energy of 0.08 eV. Defect distributions are found to shift to greater depths with increasing implantation temperature and dose. Some defects are even found farther than the accessible range of the implanted ions. RBS/C data on high-temperature implantations also suggests that defect complexes are created at high doses in addition to the point defects that are still stable at high temperature. A decrease in Raman intensity of implanted samples relative to that of crystalline samples was observed and correlated with an increase in optical absorption near the wavelength of the laser pump (514.5 nm).

Different types of microcavities for GaAs-based light emitting devices operating in the 1.3 µm spectral range are analysed. Microcavity light-emitting diodes (MC LEDs) can be fabricated with different designs of distributed Bragg reflectors (DBRs), e.g.: top and bottom AlAs/GaAs semiconductor DBRs; bottom AlAs/GaAs semiconductor and top dielectric DBRs; and oxidized Al_xO_y/GaAs DBRs. MC LEDs operating in the 1.3 µm spectral range and characterized by spectral width (13 nm) and narrow far-field pattern (<20 degrees) are reported. In the case of vertical-cavity surface-emitting lasers (VCSELs), practical implementation of injection lasing can be only achieved with oxidized Al_xO_y/GaAs DBRs, despite the fact that DBRs with nominally comparable parameters can be fabricated. It is shown that the 1.3 µm InAs/InGaAs quantum dot (QD) VCSEL exhibits remarkably low internal losses, compared with QD VCSELs operating near 1 µm. This enables use of high-reflectance DBRs, important for lasing in low modal gain media, with high (>40%) differential efficiency retained. A threshold current of <2 mA at 300 K is achieved (λ = 1.304 µm).

In this paper, a computer-based analysis is performed to study layout solutions aimed at increasing the breakdown voltage in Si-microstrip detectors. For optimum performance it is crucial to achieve maximum breakdown voltage for Si detectors operating at very high bias due to the extremely hostile radiation environment of next generation experiments such as LHC. The performance of Si-microstrip detectors can be improved by implementing floating field-limiting rings around the active detector area. A simulation study has been carried out to evaluate the distribution of breakdown voltage as a function of guard-ring spacing (GS). The purpose of this work is to find a criterion to optimize GS for multiple ring structures incorporating various physical and geometrical parameters as an aid to design optimization. Using this criterion the optimum spacing of guard rings for multiple ring structures was obtained. The proposed criterion is very robust and is insensitive to the number of guard rings, junction depth and radiation damage. The simulation results for the seven-ring design agree well with experimental measurements.

A technique to improve thin-film yield in chemical bath deposition of semiconductor thin films is presented. This involves the use of very small substrate separation, 0.1 mm, to eliminate the passive layer of the bath, which contributes solely to precipitation. At small substrate separation, a thin layer of the bath mixture is held by surface tension between pairs of substrates. The thin-film yield, which is the percentage of the metal ions in the bath utilized towards the film formation, obtained in this experimental set-up is considered to be near 100% for CuS, Cu_2-xSe, CdS and CdSe thin films. The final thickness estimated for the films is about 40-50 nm. The optical and electrical properties of these films are presented to illustrate that at such film thickness they fulfil the requirements for certain applications.

Nonlinear hot carrier transport features and related optical nonlinearities are investigated under nonuniform illumination and carrier heating in microwave (mw)-biased high-resistivity GaAs crystals. The dynamics of light-interference pattern-induced nonequilibrium carriers and evolution of internal electric field are studied in mw fields extending above a region of negative differential conductivity. We analysed the peculiarities of nonlinear transport in a spatially modulated structure at various photoexcited carrier concentrations, which was kept below its threshold for mw-induced high-field Gunn-domain grating formation. At low-illumination levels, we found a three-fold increase in the space-charge (SC) field due to electron gas heating. At higher light intensities, enhancement of the internal field is determined by a fast screening of the external mw field and the transport of nonuniformly heated carriers. Hot carrier transport effects in a region of negative differential conductivity, even at nearly homogeneous but high illumination, lead to SC-wave formation with amplitudes, which may exceed the diffusive SC-field amplitude by 100 times. The latter effect was confirmed experimentally using a four-wave mixing technique in mw-biased GaAs crystals and short laser pulses.

The atomic structure and electrical and optical properties of amorphous AsSe films prepared by thermal evaporation in a vacuum and by rf ion-plasma sputtering have been studied. The conductivity, activation energy of conductivity, optical gap, radii of the first and second coordination spheres, number of the nearest neighbours of arsenic and selenium atoms in the first coordination sphere and dimensions of the medium-range order domain in the atomic structure have been determined for the samples studied. Films prepared by different methods have dissimilar electrical and optical parameters and show differences in atomic structure, mainly related to the dimensions of the medium-range order domains. A conclusion is made that it is the medium-range order in the amorphous film atomic structure in the As-Se system that governs the electronic structure of amorphous films of the As-Se system.

A theoretical design evaluation of a GaAs/GaInAs/GaInP-based 980 nm pump laser is presented. Using self-consistent two-dimensional numerical simulation, the layer structure of the laser diodes is optimized. A ridge waveguide design with GaInAs/GaAs and GaInAs/GaInAsP waveguide regions has been simulated. Compared to multiple quantum wells, a single quantum well with a GaInAsP/GaAs barrier layer gives lower threshold current. Compared to GaInAs/GaAs, the GaInAs/GaInAsP waveguide region suffers from a larger spread in the threshold current due to non-uniformities in the carrier density with increasing quantum wells. The influence of the well and waveguide thickness, and ridge width on the threshold current, is studied. The simulations have resulted in characteristic temperatures of 160 and 360 K for the GaInAs/GaAs and GaInAs/GaInAsP structures, respectively.

Extended x-ray absorption fine-structure measurements have been performed on ZnSe crystals doped with Er by an addition of ErF₃ during growth. The results show that Er exists in these samples in an orthorhombic configuration with nine nearest F neighbours similar to that in orthorhombic ErF₃. The energy level splittings observed in optical absorption and photoluminescence investigations in the region of the ⁴I_15/2↔⁴I_13/2 transitions at 1.54 µm are fully consistent with the orthorhombic symmetry of the Er centre.