The work reported here deals with studying the defects induced by heavy ion implantation as well as the degree of crystalline lattice recovery after annealing in a high purity argon environment between 600 and 1600 °C. We implanted 6H, n-type silicon carbide with Pd and Au ions at 1015 ions/cm2, and used Micro-Raman (MR) and optical absorption (OA) spectroscopy techniques for investigating the lattice properties and damage evolution at various stages during the fabrication process.

An optical-capacitance-transient spectroscopy (O-CTS) method was used to characterize the defects in 3C-SiC on Si. The O-CTS measurement enables us to estimate optical threshold energy and optical cross section for the defects. In the O-CTS spectrum, a peak was observed for photon energy hv larger than 0.5 eV. This peak was thought to be due to the ND1 center, which was also observed by deep level transient spectroscopy (DLTS) and found to have a thermal activation energy of 0.37 eV. The optical cross section for the center increased with hv for hv<0.6 eV and then decreased with increasing hv. The apparent optical threshold energy was about 0.47 eV. Another deep levels which have optical threshold energy of around 1.4 eV were also observed.

We report a new poly-Si TFT, of which the troublesome implantation damage near the source/drain junction was eliminated, by performing source/drain ion implantation as well as excimer laser annealing (ELA) prior to the gate formation. The recrystallization of a-Si in the channel region and the dopant activation in the source/drain region were simultaneously accomplished by single ELA process step so that the implantation damage, which results in large leakage current of TFT, has been successfully eliminated. TEM image verifies that large poly-Si grains were successfully grown from the ion implanted source/drain region to the channel region. The proposed poly-Si TFT, of which mobility is 171 cm2/Vs, exhibits a large on/off current ratio exceeding 4.1 × 107 without LDD or offset structure while those of the conventional TFT, which has been fabricated simultaneously for the comparison purpose, are 86 cm2/Vs and 6.1 × 106.

Hydrogen incorporation in n-type Si-doped GaAs epilayers is now a well-known process. This paper is devoted to the study of the stability of SiH (SiD) complexes when submitted to an electron beam in n-type Si-doped GaAs epilayer and also in 2D-AlGaAs heterostructures exposed to a hydrogen or deuterium plasma.

The results obtained by Hall effect measurements on hydrogenated and deuterated GaAs epilayers with different thicknesses (0.2 and 0.35νm) and Si planar-doped AlGaAs/GaAs/InGaAs heterostructures exposed to an electron beam with different injection energies (10 to 50 keV) are presented. On one hand, the reactivation of Si dopants strongly decreases when deuterium is used. On the other hand, the study of this reactivation versus injection energies of electrons suggests an energetic electron excitation effect rather than a minority carrier generation effect. In addition, for the 0.2νm thick GaAs epilayer and the 2D heterostructures, the free carrier density does not vary significantly for low electron densities, and as a consequence, the reactivation of the Si dopants occurs above an electron dose threshold. This phenomenon might be attributed to the filling of surface states as the dopants are progressively reactivated.

As a result, due to the electron dose threshold as well as their high electron mobility properties, Si planar-doped AlGaAs/GaAs/InGaAs heterostructures are particularly interesting to reactivate dopants, with a good spatial contrast, using an electron beam irradiation and the effects described in this paper could open the fabrication of high mobility 1D or 2D mesoscopic structures for electronic or optoelectronic applications.

In this paper, deep level defects in undoped and Si–doped GaN have been studied using digital deep level transient spectroscopy. Common trap levels at Ec -ET ∼ 0.15-0.20 eV and 0.59-0.62 eV were detected for both undoped and Si-doped samples. For the doped samples, three additional defect levels at Ec-Et ∼ 0.11, 0.28, and 0.45 eV were detected. The concentration of the 0.15-0.20 eV was found to be much higher in undoped GaN that also shows higher dislocation density. Based on this correlation and the logarithmic capture behavior observed for this level, indicative of extended defect nature, we attribute the 0.15-0.20 eV level to dislocation related defects. On the other hand, the 0.28 and 0.45eV trap levels are tentatively attributed to Sirelated defects simply due to the fact that these two levels were observed only in Si-doped GaN. The 0.11eV trap level, which exhibits an exponential capture kinetic, is believed to be related to nitrogen vacancies.

The spatial dependence of the band-gap light-emission energy of AlxGa1-xN alloys at composition 0≤ × ≤1 was studied via deep UV-photoluminescence (PL) and Raman microscopy. The data were acquired in a random fashion from an area of ∼ 1mm2 on the sample at steps of ∼1 νm - 200 νm utilizing the 244 nm laser line of probing spot size ∼300 nm radius. Our study indicates that the PL emission energy exhibits random type variations depending on locality: the alloys of composition x=0.12, x=0.22, and x=0.70 exhibit variations of ∼ 10 meV, 30 meV, and 25 meV respectively. The PL of the pure GaN exhibits no spatial dependence while the alloy of x=0.50 exhibits a variation around ∼ 45 meV. Moreover, the functional dependence of the band-gap Eg, on the composition was found to be Eg(x)=3.4(1-x)+6.2x-1.2x(1-x) from which the compositional variation, δx, can be computed for a given variation in the PL emission energy after accounting for the stress effect in the alloys.

Thin-film CdTe solar cells are very promising for future cost-effective photovoltaics. The photovoltaic effect in these cells is based on the extraction of photoexcited carriers by the field provided by the CdTe/CdS heterojunction. An additional interface with non-rectifying characteristics is needed to close the external circuit on the other side of the CdTe thin film. Finally, the transport of photoexcited carriers is influenced by the presence of grain boundaries (GBs). In this contribution, we investigate several aspects of these interfaces and their effects on the operation of CdTe solar cells by electron-beam-induced current (EBIC) and cathodoluminescence (CL) measurements.

GaN thin films were grown on porous SiC substrates using reactive molecular beam epitaxy with ammonia as the nitrogen source. Microstructure analysis and optical characterization were performed to assess the quality of the effect of pores on the growth and the quality of the GaN films. Results indicate that the GaN films on porous SiC are slightly less defective and more strain-relaxed (some completely relaxed) when grown on porous SiC substrate, as compared to growth on standard 6H-SiC substrates. Rocking curve FWHMs of 3.3 arcmin for (0002) diffraction and 13.7 arcmin for (1012) diffraction were obtained for sub-micron thick GaN films. Excitonic transition with FWHM as narrow as 9.5 meV was observed at 15K on the GaN layer grown on porous SiC without a skin layer.

Carbon-doped GaN was grown by plasma-assisted molecular-beam epitaxy using carbon tetrachloride vapor as the dopant source. For moderate doping mainly acceptors were formed, yielding semi-insulating GaN. However at higher concentrations p-type conductivity was not observed, and heavily doped films (<5×1020 cm-3) were actually ntype rather than semi-insulating. Photoluminescence measurements showed two broad luminescence bands centered at 2.2 and 2.9 eV. The intensity of both bands increased with carbon content, but the 2.2 eV band dominated in n-type samples. Intense, narrow (∼6 meV) donor-bound exciton peaks were observed in the semi-insulating samples.

The effects of H irradiation and thermal annealing on the optical properties of (InGa)(AsN) heterostructures have been investigated by photoluminescence (PL) and infrared absorption, as well as by theoretical methods. It has been found that different N clusters contribute to the band gap red-shift reported for (InGa)(AsN) alloys, with a sizable localization of the carrier wavefunctions around N atoms. Infrared absorption measurements indicate that two different NH complexes are formed, whose vibrational frequencies are in good agreement with theoretical estimates. The ability of hydrogen to passivate different isoelectronic impurities is confirmed by PL results in H irradiated Zn(STe).

We theoretically investigated interactions between nitrogen (N) atoms and Si native defects, vacancy (V) and interstitial (I), by using first-principles calculations in order to shed light on the nitrogen-doping effect on the defect aggregation processes. Stabilities of various N-I and N-V complexes are examined by calculating the total energy. We found that N atoms form stable complexes with both of V and I. The formation of such stable complexes reduces the effective concentrations of the native defects, resulting in the suppression of aggregation processes of V and I.

We report the growth of GaN films by RF-MBE on SiC, ZnO, and LiGaO2 substrates, without buffer layers. Structural and optical properties of the films were probed by AFM for surface morphology, XRD for crystalline structure, and PL for optical properties. The dependence of GaN layer quality on the substrates and their surface pre-treatment prior to growth was studied within a similar MBE growth parameter matrix for all samples.

Thermal donor formation was studied in oxygen enriched high resistive float zone silicon (FZ Si:Oi). Such substrates are used e.g. for radiation hard detectors or high voltage devices. RF Plasma hydrogenation (110 MHz, 50 W) was carried out at 250°C for 1 hour. Subsequent annealing was done at 450°C/air for up to 50 h. The plasma treated and annealed FZ Si:Oi samples were analyzed by spreading resistance probe, capacitance-voltage and DLTS measurements. It is shown that a rapid formation of donors can be observed in oxidized FZ Si:Oi, but in a somewhat different way than in Czochralski (Cz) Si. While in Cz Si the hydrogen enhanced formation of ‘old’ thermal double donors occurs under the applied processes, in FZ Si:Oi most probably the formation of new hydrogen related shallow donors can be assumed.

Room-temperature electric investigations carried out in CO2-laser irradiated ZnCdHgTe epifilms revealed current-voltage and capacitance-voltage dependencies typical for the metal-semiconductor barrier structure. The epilayer surface studies had demonstrated that the cell-like relief has replaced the initial tessellated structure observed on the as-grown samples. The detailed numerical analysis of the experimental measurements and morphological investigations of the film surface showed that the boundaries of the cells formed under the laser irradiation are appeared as the regions of accumulation of derived charged defects of different type of conductivity supplying free charge carriers under the applied electric field.

Coupling of scanning tunneling microscopy (STM) with various schemes of optical spectroscopy was found to provide powerful tools for study of crystalline defects in bulk semiconducting solids. The simplest method was applied to a subsurface defect in a bulk GaAs crystal in which the signal was acquired by detecting the change in the tunneling current reflecting a local surface swelling that occurs when the wavelength of the chopped light used for spectroscopic measurements coincides with a photoabsorption spectral peak of the defect. Another scheme using a continuous light of variable wavelength was applied to midgap centers, assigned as arsenic antisite defects, densely populated in low-temperature-grown GaAs epifilms. Experiments at 90K revealed that light illumination causes reversible transformation of the individual defects to a metastable state with an excitation spectrum very close to one observed for the photo-quenching effect of EL2 centers in bulk GaAs.

In this letter, we investigated the correlation between as-grown surface morphologies and Mn compositions of Ga1-xMnxAs epilayers - a III-V diluted magnetic semiconductor - grown by liquid phase epitaxy (LPE). Ga1-xMnxAs epilayers were grown at 595 °C from 50 % Ga + 50 % Bi mixed solvent. The grown layers were characterized by energy dispersive x-ray analysis (EDS) and atomic forced microscopy (AFM). The Mn composition measured by EDS after growth process was varied from 1 to 7 %. As increasing Mn composition surface morphologies of as-grown Ga1-xMnxAs epilayers were varied. At higher Mn compositions, the morphology of the surface layers degrades strongly, preventing removal of the solution-melt from it. Key words: LPE, as-grown, surface morphology, Mn composition, Ga1-xMnxAs, energy-dispersive x-ray analysis (EDS), atomic forced microscopy (AFM).

Copper in silicon is a feared contaminant in device processing. It diffuses quickly as an interstitial and forms electrically active precipitates that are difficult to dissolve. Several complexes assigned to copper pairs have been observed but have yet to be unambiguously identified and fully characterized. We present the results of joint theoretical-experimental studies of several pair structures. The theoretical work involves ab-initio molecular-dynamics simulations, and the results include configurations, binding energies, electronic structures, vibrational modes and formation dynamics. The experimental work combines electrical and optical techniques. One characteristic of the photoluminescence spectra is the presence of phonon replicas that imply the existence of very similar low-frequency and localized vibrational modes in two distinct copper pairs. These modes are theoretically identified.

Standard p- and n-type Czochralski (Cz) silicon wafers were hydrogenated by a RF (13.56 MHz) hydrogen plasma at moderate temperatures (250 °C). After plasma hydrogenation and subsequent annealing up to 600 °C the formation and of H2 molecules in voids and platelets was investigated by Raman spectroscopy. The Raman intensities of the H2 vibration modes at ∼ 4150 cm-1 exhibited significant intensity modulations in dependence on the annealing temperature. The intensities of the H2 Raman lines indirectly monitor the evolution of the voids and platelets upon annealing. This assumption was verified by cross-sectional transmission electron microscopy (XTEM), which was applied for comparison. The intensity modulations of the H2 Raman signal can be explained by the evolution of the well known {111} and {001} platelets. At lower annealing temperatures (< 500 °C) platelets laying in {111} planes are dominant, while at elevated temperatures (> 500 °C) [001]-oriented platelets become more and more important. In addition in p-type material by XTEM also {110} platelets could be observed.

Cryogenic operation of the diamond surface-channel field-effect transistors (FETs) is investigated. Metal-insulator-semiconductor FETs (MISFETs) are fabricated using CaF2 as a gate insulator. MISFETs operate successfully even at 4.4 K. At low temperature, field-effect enhances the drain current, even if the surface holes become almost frozen-out. Channel mobility increases as temperature decreases to 4.4 K, which indicates the reduced phonon scattering.

We investigate by photoluminescence (PL) nominally undoped, commercially available Zinc Oxide substrates (from Eagle Picher) grown by seeded chemical vapor transport technique in order to identify residual donors and acceptors. In low temperature PL spectra the dominant emission comes from the decay of bound exciton lines at around 3.36 eV. Zeeman measurements allow the identification of the two strongest lines and some weaker lines in-between as donorrelated. From the associated two-electron satellite lines binding energies of the major donors of 48 meV and 55 meV, respectively, can be deduced.