Lattice-mismatch induced defects have been studied by means of deep-level transient spectroscopy (DLTS) in two types of GaAs-based heterostructures, GaAs/InGaAs and GaAs/GaAsSb, and in a GaN-based laser-diode heterostructure grown on a bulk GaN substrate. DLTS measurements, carried out with p-n junctions formed near the heterostructure interfaces, revealed three deep-level traps in the investigated structures, which have been related to dislocations on the grounds of their logarithmic kinetics for capture of charge carriers into the trap states. An electron trap at $E_{\text C}-0.64$ eV and a hole trap at $E_{\text V}+0.67$ eV, found in the GaAs-based structures, have been attributed, respectively, to threading and misfit dislocations. An electron trap at $E_{\text C}-0.23$ eV, found in the GaN-based structure, has been tentatively related to dislocations in a p-type layer of the structure. Detailed investigation of the dependence of DLTS-line amplitude and its shape on the filling time of the traps with charge carriers allowed us to specify the type of electronic states associated with the traps.

The first experimental results about the growth and characterization of Pb1−xCdxTe new high-Z ternary alloy, grown by Vapour Phase Epitaxy (VPE) onto CdTe single crystal substrates are presented. SEM images have shown a well-defined interface between the substrate and the heterostructure bulk, without voids or inclusions. EDX analysis in a line scan mode was done over the layer crossections. The Te, Pb and Cd concentration profiles were found, verifying a strong inter-diffusion in the metallic sublattices and confirming the existence of the Pb1−xCdxTe ternary alloy. This has been also confirmed by X-ray diffraction measurements. For the longest growth times, two types of surface defects arose: PbTe aligned microcrystals and cylindrical-like Te-rich structures. Hall measurements showed that the carrier concentration of the layers decreases and the resistivity increases when the growth temperature increases. The influence of the surface defects on the electrical properties was also demonstrated.

The thermal emission rate of dominant traps in molecular beam epitaxial n- and p-type AlGaAs subjected to Ar-ion beam etching has been studied by deep level transient spectroscopy. Emission signatures were determined and compared with results obtained by other authors for irradiation induced and grown-in defects in GaAs and AlGaAs. The most significant result of this study is the observation that the process-induced defects in n- as well as p-type AlGaAs exhibit emission signatures, which are characteristic of native defects found in GaAs. The effect is discussed in terms of a compensation effect and related band bending.

In organic light emitting diodes (OLEDs), localized traps within the band gap of the organic semiconductor play a fundamental role in the light emission process. Trapped charge carriers cannot recombine efficiently and therefore do not contribute to the emission. The determination of the trap parameters in the emitting layer is especially important in the evaluation of the efficiency of such devices. We have investigated the trap parameters in some organic semiconductors using the Charge-Based Deep Level Transient Spectroscopy (Q-DLTS) technique. Examples are given in poly(p phenylene vinylene) or PPV and 4, 4'-bis(4-dimethylaminostryryl) or DMASB, for which the trap level, the trap density, and the capture cross section were determined. In addition, it was possible to identify the carrier type (minority and majority) traps in these semiconductors. The results were compared with those obtained in similar materials by other techniques such as conventional DLTS, thermally stimulated currents (TSC), impedance measurements. Q-DLTS appears to be a powerful tool for studying defects in organic semiconductors.

Thermally stimulated current (TSC) and photo induced current transient spectroscopy (PICTS) were used to investigate deep traps in oxygen-rich medium resistivity GaAs. We observed an abnormal behaviour of the TSC signal at a temperature of about 200 K, where the TSC current is lower than the dark current. This results in a negative peak occurring in the temperature range where the signal of the well known EL3 defect in undoped semi-insulating GaAs is present. For verification, comparative PICTS-measurements were performed, which exhibit the same negative peak at similar temperatures. The activation energy for this negative peak was determined to be ~ 0.6 eV (TSC). This is in good agreement with published values for the EL3 ranging from 0.56 to 0.68 eV. Furthermore, we illustrate that the depth of the peak increases with increasing oxygen content. Our results support the assumption, that oxygen on an arsenic site – the so called off centre oxygen oc-OAs – should be the origin of the EL3.

Cathodoluminescence (CL) microscopy and spectroscopy have been used to investigate the nature and spatial distribution of defects and impurities in n-type epitaxial 4H-SiC. CL microscopy reveals the existence of 6H-SiC polytype inclusions, while CL spectra recorded at different excitation conditions show luminescence emission related to deep levels in the SiC epilayer. Deconvolution of the mentioned spectra indicates the complex character of the deep-level CL emission, that is actually composed of four bands centred near 2.72, 2.56, 2.42 and 2.00 eV at 88 K. The origin of these bands is discussed considering previous deep level transient spectroscopy measurements carried out in the same material investigated in the present work.

Silicon Carbide (SiC) is a wide band gap semiconductor, having opto-electronic properties that are suitable for many applications. Some structural defects due to crystal growth and/or doping technologies are commonly present in the substrates of SiC. The $(11\bar{2}0)$-oriented 4H-SiC bulk wafers are particularly investigated, due to some advantages with respect to the (0001)-Si face. One of these advantages is a better crystal reordering during post-implantation annealing. In this paper cathodoluminescence (CL) and X-Ray topography measurements have been carried out in order to investigate the optical and structural properties of commercial $(11\bar{2}0)$ 4H n+-type substrates.

UV scanning photoluminescence spectroscopy is applied to 4H-SiC epitaxy characterization. In a first part, the technique is used for triangular defects characterization. The results show that two kinds of defects are present. Some defects are inclusion of cubic SiC which is confirmed by Raman spectroscopy. The other ones consist of staking faults of different thicknesses acting as quantum wells. In a second part, the effective lifetime profile is mapped for a whole 50 mm epitaxy using the variation of room temperature PL intensity versus excitation intensity.

The influence of different annealing procedures on both structural and electrical characteristics is investigated for 6H-SiC implanted with nitrogen in the doping concentration range of 1 × 1018 − 1 × 1020 cm−3 by Transmission Electron Microscopy and Scanning Capacitance Microscopy. The poor electrical activation of N+ ions is correlated to the formation of a high density of precipitates in the implanted layer when increasing the doping concentration. A rapid thermal pre-annealing combined with conventional furnace annealing is effective to improve the active fraction but the presence of the precipitates overwhelms this effect for high doping concentration (> 1 × 1019 cm−3).

A high density of planar defects is observed by scanning and transmission electron microscopy in wafers cut from 4H-SiC crystals containing nitrogen above about 2 × 1019 cm−3 and heat treated at 1100 °C. All of the planar defects observed by high-resolution transmission electron microscopy have the same structure comprising six Si-C bilayers in cubic stacking sequence. Such a lamella can originate from two stacking faults in neighbouring basal planes and is therefore called double stacking fault. The recently proposed quantum well model of the electronic structure of the double stacking faults is used to explain the characteristic luminescence band at about 500 nm and the strong anisotropy of the electrical resistivity in the heavily doped, heat treated wafers.

In this communication, results are presented of the application of etching in molten E+M etch (KOH-NaOH eutectic mixture with 10% MgO) for studying defects in GaN. The method was used to study defects on differently oriented cleavage and basal planes of GaN single crystals, MOCVD-, MBE- and HVPE-grown epitaxial layers and LD and LED structures. Dislocations, dislocation loops and stacking faults have been revealed on $(10\, \bar{\text{\scriptsize 1}}\, 0)$, $(1\,\bar{\text{\scriptsize 2}}\,10)$ and $\{0001\}$ Ga- and N-polar planes. Diversified etch pit morphology was observed depending on the crystallographic orientation of the etched samples and was correlated with the crystallographic symmetry of the GaN lattice. Etching results were calibrated using TEM analysis.

The measured phonon-density of states of bulk GaN by time-of-flight neutron spectroscopy has been recently reported by Nipko et al. [CITE]. The authors have also calculated the true partial and total DOS as well as the phonon dispersion curves along major symmetry directions in the Brillouin zone. However, the group-theoretical phonon assignments have not been provided. Based on calculated symmetry allowed modes spanned by displacement representation and on the derived connectivity relations along the major directions in the Brillouin zone we have assigned Nipko's phonon dispersion curves to irreducible representations (species) of the $C^4_{6v}$ (P63mc) space group of GaN.

Heteroepitaxial GaN layers grown on sapphire by metal organic vapour phase epitaxy (MOVPE) have been characterised by conventional transmission electron microscopy (TEM) on planar and cross-sectional samples, Large Angle Convergent Beam Electron Diffraction (LACBED) and by high-resolution transmission electron microscopy (HRTEM). Hollow tubes termed nanopipes were resolved on planar view and cross-sections of heteroepitaxial GaN. For advanced studies of the nature of nanopipes the LACBED method was employed. The recognition between perfect structure and screw distortion around nanopipes was performed with high accuracy using Zone Axis LACBED images.

A detailed transmission electron microscopy study is performed on the pyramidal inversion domains that appear in highly Mg-doped GaN grown by metalorganics vapor phase epitaxy or by the high-pressure, high-temperature method. From a comparison between high resolution images of the inversion domain boundaries and simulations using different atomic models, we conclude that both basal and inclined domain boundaries are likely formed of a monomolecular layer of the definite compound Mg3N2. We show that, due to their high concentration, the formation of these defects may account for auto-compensation in Mg-doped GaN. We also show that the local band bending induced by the polarity inversion due to these defects can be at the origin of the blue luminescence of highly Mg-doped GaN, always observed when nanometric pyramidal inversion domains are also present.

Due to high lattice mismatch, heterostructures of III-nitrides are subject to plastic relaxation. In this paper, we focus on the relaxation of AlGaN films grown on GaN. This relaxation is realised by cracking followed by the introduction of misfit dislocations. We describe those mechanisms and present a method to grow thick high quality crack-free AlGaN layers. This method uses jointly plastic relaxation and lateral growth.

Two samples, GaN silicon-doped and GaN magnesium-doped, were hydrogen implanted and annealed. The low temperature photoluminescence and inelastic light scattering spectroscopy were employed to investigate structural changes as well as the changes in optical electronic transitions.

In order to improve the crystal quality of GaN-based light emitting devices, photoluminescence (PL) characterization of below-gap states in plasma assisted MBE-grown GaN/AlGaN quantum well (QW) structures has been done by utilizing a below-gap excitation (BGE) light in addition to an above-gap excitation light. The decrease of the band-edge PL intensity due to the addition of the BGE of 1.17 eV indicates the presence of an energy-matched below-gap state in the two-wavelength excited PL. In continuation to our previous efficiency improvement by applying modulation-doping to GaAs/AlGaAs QW's, we focused on several undoped and Si-doped GaN/AlGaN QW's. Experimental results showed that Si modulation-doping reduces the density of below-gap states in the QW region, hence it is promising for increasing internal quantum efficiency of GaN-based QW's.

Photochemical (PEC) etching and transmission electron microscopy (TEM) have been used to study the defects in hetero-epitaxial GaN layers. TEM proved that PEC etching reveals not only dislocations but also nanopipes in the form of protruding, whisker-like etch features. It is shown by diffraction contrast techniques that the nanopipes are screw coreless dislocations. An example is shown of the transformation of a normal full-core screw dislocation into a nanopipe. The PEC/TEM experiments indicate the presence of electrically active (recombinative) species in the vicinity of the nanopipes.

To study the material deterioration at and around the support contacts during processing of silicon wafers, we used Rockwell indentation at elevated temperatures as a model. Cz-silicon was subjected for 30 s to a load of 1.5 N, at temperatures between 70 °C and 660 °C. The resulting morphology was checked by Scanning Electron Microscopy. Micro Raman Spectroscopy was used to monitor residual stress and the occurrence of silicon polymorphs. We found strong compressive stress inside the indented area, with a dramatic drop and reversal to tensile stress at its boundary. The morphology shows a top hat profile, covered with a mesh of vein-like structures. Crystalline phases such as Si-III, Si-IV, Si-XII, and amorphous silicon are observed. Outside the spot, the situation depends strongly on the indentation temperature. Up to 400 °C the material appears practically unstressed, with a high density of relaxation cracks. At 500 °C and 600 °C a transition is found from strong tensile stress at the boundary to another region of compressive stress extending over more than 40 μm, associated with a significantly lower crack density. At still higher temperature (660 °C) the crack density tends to zero, and comparably weak stress seams to oscillate between compressive and tensile.

Co-sputtered Si-rich SiO2 films annealed at 1150 °C are studied by photoluminescence and EPR methods. It is found that the emission spectrum of as-prepared samples contains one broad infrared band. It is shown that one-year aging in ambient air and low-temperature annealing in an oxygen atmosphere leads to an increase in the infrared band intensity and the appearance of additional bands with maxima at 1.7 eV, 2.06 eV and 2.3 eV while annealing in a hydrogen atmosphere results in the decrease of the 1.7 eV and 2.06 eV band intensities. A correlation between the 1.7-eV band intensity and the EPR signal from EX-centers is found to exist. The decrease of crystallite sizes results in a high-energy shift of the infrared band while the peak positions of the other ones (at 1.7 eV, 2.06 eV and 2.3 eV) do not change. The infrared band is ascribed to recombination in Si crystallites while the others are attributed to silicon oxide defects, the 1.7-eV and 2.06-eV bands being due to oxygen-excess defects such as EX-center and NBOHC.