We report on spectroscopic photoluminescence (PL) mapping of solar-cell-grade mc-Si ribbon wafers. We observe under UV excitation a broad visible emission from the SiNx:H layer. The samples covered with SiNx:H were subjected to rapid thermal processing at different temperatures, and PL maps were measured before and after treatment. We observed that after RTP treatment the intensity of the PL band was significantly increased, which indicates further reduction of non-radiative defects. The magnitude of these increases depends on the RTP conditions. The visible PL band exhibits a reversible photo quenching of the intensity under 325 nm HeCd laser excitation. The PL intensity can be recovered by annealing with the rate exhibiting a thermally activated behavior. The observed PL photo quenching reveals a metastable process in the SiNx:H film under UV excitation. We demonstrate the possibility of creating a reversible luminescence micro-pattern on the SiNx:H layer using a focused UV laser beam.

The high power RF device performance decreases as the operation temperature increases (e.g. fall of electron mobility impacting the cut-off frequencies and degradation of device reliability). Therefore the determination of device temperature is a key issue for device topology optimisation. In this work the temperature variation of AlGaN/GaN high-electron-mobility transistors grown either on silicon or sapphire substrates under bias operation was measured by micro Raman scattering spectroscopy. The differences in thermal resistance for similar devices grown on the two different substrates were assessed. The thermal resistances of different device topologies were compared in order to optimise the component design. The temperature measurement across the gate and along the component fingers were made to quantify the thermal gradient of the device. Temperature measurement up to a power dissipation of 16 W for a 4 mm development device was carried out and the peak temperature of 650 K was determined.

The in-plane optical anisotropy of several GaAs/AlGaAs quantum well samples with different well widths has been measured at room temperature by reflectance-difference spectroscopy (RDS). The RDS line shapes are found to be similar in all the samples examined here, which dominantly consist of two peak-like signals corresponding to 1HH$\rightarrow$1E and 1LH$\rightarrow$1E transition. As the well width is decreased, or the 1 ML InAs layer is inserted at one interface, the intensity of the anisotropy increases quickly. Our detail analysis shows that the anisotropy mainly arises from the anisotropic interface roughness. The results demonstrate that the RDS technique is sensitive to the interface structures.

Defects in oxygen-containing Czochralski silicon (Cz-Si) subjected to 2-steps pre-annealing at 720–1000 K under 105 Pa and next treated at 1170–1400 K (HT) under high hydrostatic pressure (HP, up to 1.2 GPa) were investigated by photoluminescence, infrared absorption and related methods. Microstructure of HT − HP treated Cz-Si is critically dependent on nucleation centres for oxygen precipitation created by pre-annealing.

A distortion of exciton emission spectrum, namely, relative decrease of free exciton band intensity with respect to that of its phonon replicas in undoped as-grown ZnO single crystals has been shown to result from enhanced reabsorption of shorter wavelength emission in the crystal due to formation of optical absorption tail. Some crystal imperfections, in all probability, dislocations decorated with shallow donors are supposed to be responsible for the effect.

Based on the well established group—theoretical methods we have calculated the Clebsch—Gordan coefficients (CGCs) for some crystals of the space group C46v. The linear combinations of the CGCs determine the elements of the first order scattering tensors while the second order scattering tensors are bilinear combination of the CGCs. Some other applications of the calculated CGCs are also discussed.

Recombination processes in GaAsN, GaInAsN, and GaAsSbN compounds have been analysed and compared. The following properties like: broad photoluminescence band at energy of ~ 0.85 eV, an emission band aproximately 80 meV below band gap energy, and annealing-induced blue shift of the energy gap have been found for all three compounds. In order to explain these features a simple band gap diagram with N defect-related levels close to conduction band edge and fluctuations in the energy of the conduction band minimum has been proposed.

Radioactive 57Mn+ ions have been implanted into a natural diamond held at 300–1100 K for Mössbauer spectroscopy studies on the 14 keV γ-radiation emitted in the decay of the 57Fe daughter atoms. The Mn parent isotopes are found to be implanted into defect sites of non-cubic symmetry, which anneal partially with increasing temperature during the 57Mn lifetime. This is concluded to lead to their incorporation on substitutional lattice sites. This site is inherited by the majority of the 57Fe daughter atoms, however, a sizeable fraction is expelled into interstitial sites owing to the recoil in the nuclear $\beta^-$-decay. Thus the Fe isomer shifts in both lattice sites have been determined.

It is interesting to consider the problem of the presence of defects in the semiconductor binary compounds by observing their elemental tetrahedron distortions, caused by the creation of vacancies and interstitial atoms within the tetrahedra and so on. Our model thus considers the system A(VzxZ$_{1-x}$) and (A$_{1-y}$Vay)Z as composed of five defect tetrahedron configurations where A is a cation atom, Z an anion atom, Va-cation vacancy, Vz-anion vacancy. In this communication we present far IR (FIR) spectra obtained at the DAFNE facility of Laboratori Nazionali di Frascati (INFN) using its synchrotron radiation. Two samples of CdTe are considered: sample-1 was grown by the PVT technique and sample-2 using the same technique but on the basis of, polycrystalline CdTe previously purified from oxygen in hydrogen atmosphere.

Raman scattering (RS) experiments have been carried out to determine both residual strain and alloy composition in a bulk Si1−xGex single crystal with compositional gradient, which can be used as a focusing and diffracting X-ray monochromator. Since RS results are influenced both by strain and by composition, it is difficult to determine them separately from the observed phonon position. By analyzing strain effect on RS in connection with a strain model developed for bulk mixed crystals, both residual strain and alloy composition are evaluated. It is found that the alloy composition evaluated from the RS results is in good agreement with that measured by the standard chemical analysis. It is also found that the axial and radial strain components vary from −0.76×10−3 to −1.2×10−3 and 3.6×10−4 to 5.7×10−4, respectively, for the almost linear variation in composition from 0.034 to 0.055.

Optical (refractive index) and structural properties of silicon oxynitride (SiON) and amorphous silicon (a-Si) multilayers grown by RF sputtering with thickness in the 10–30 nm range have been analysed by ellipsometry and TEM. Satisfactory agreement between the two techniques is obtained as regards the thickness determination of the SiON films. Disagreement with values obtained by the stylus method by extrapolation for the two types of layers is discussed. The interfaces of the SiON films are very good when n-type P doped Si is used as a target. They are wavy with average periodicity and amplitude on the order of 50 and 2 nm, respectively, when a semi-insulating Si target is used, despite the presence of a buffer layer. Hypothesis is made that P incorporation may improve the reconstruction of the SiON surface.

GaInP layers were grown on GaAs substrates by MOVPE at low pressure in the temperature range between 525 and 600 °C. A detailed analysis of the optical properties of these samples was performed by means of Photoluminescence, Cathodoluminescence and microRaman spectroscopies, aiming to understand the contributions of composition fluctuations, strain, Cu-Pt type ordering, etc., to the properties of the layers. The composition gradients due to the horizontal flow reactor were specifically evaluated by Photoluminescence mapping. The luminescence parameters were analysed in terms of composition, order and strain by Cathodoluminescence imaging. On the other hand, ordering was observed to depend on the growth rate.

We have characterized threading dislocations (TDs) and misfit dislocations (MDs) in a degraded strained-Si/SiGe heterostructure by using electron beam induced current (EBIC), transmission electron microscopy (TEM) and chemical etching techniques. The strained-Si layer in this degraded heterostructure was selected to be thicker than the critical thickness for introducing MDs at the interface of strained-Si/SiGe. Cross-sectional TEM image reveals that there are dense dislocation network in deep region (graded SiGe layer) and 60° MDs at the upper interface (strained-Si/SiGe interface). The EBIC image taken with a 20 keV electron beam reveals the cross-hatch pattern of MD network in the deep graded SiGe region. The EBIC image taken with a 4 keV electron beam at 65 K shows weak dark spots and two perpendicular sets of weak dark lines, corresponded to TDs and MDs at the upper interface, respectively. Comparison with chemical etching results indicates that the weak dark lines in EBIC image correspond to MD bundles/groups at the upper interface. The electrical activities of these dislocations are discussed by using the temperature dependence of EBIC contrast.

The interest in virtual substrates, consisting of standard Si substrates overgrown with SiGe strain-relaxed buffers (SRBs), is mainly driven by applications in MOSFETs. They require thin SiGe layers with a high Ge content, a high degree of relaxation, smooth surfaces, and a low threading dislocation density. To fabricate such SRBs, we have developed a two-step MBE method. The first step is carried out at low temperature (LT) and introduces a supersaturation of point defects. In the second step, growth continues at a conventional MBE temperature. During this stage, the point defects introduced in the first step enable a high degree of strain relaxation, a smoother surface, and a lower defect density. The most critical process parameter is the growth temperature during the first (LT) step. If the temperature is too high, sufficient relaxation will not occur because the concentration of point defects is insufficient. When the temperature is too low, the concentration of point defect becomes too high and causes structural disorder. We have found a process window in which a high degree of relaxation and good crystal quality are achieved in sub-100 nm layers. To characterize the surface morphology and defects in the layers, various methods of optical, atomic force, and transmission electron microscopy have been employed.

Self heating during long-term DC-aging is found to be responsible for the degradation of the electrical and optical characteristics of blue p-GaN/p-AlGaN/InGaN/n+-GaN/SiC LEDs. Electroluminescence and Cathodoluminescence studies reveal an additional large optical band, not observed in unstressed devices, on the p-type side of the LEDs. Deconvolution procedures shows the band, peaked at about 3.1 eV, is due to three main emissions at 2.93, 3.08 and 3.23 eV. Deep Level Transient Spectroscopy reveals the presence of four traps for majority carriers in p-type GaN. A comparison with the optical spectra suggests three of them (at 0.12, 0.22 and about 0.5 eV) are responsible for the additional emissions after stress, while a further trap at 1.21 eV is considered non-radiative in nature. A thermally activated mechanism inducing the dissociation of native Mg-H complexes and the subsequent formation of metastable Mg-H2 complexes is considered responsible for the LED degradation. The hypothesis is supported by high power electron beam irradiation during Cathodoluminescence studies which induced a complete disappearance of the band at 3.1 eV as a consequence of the dissociation under energetic electron beam of the metastable Mg-H2 complexes.

The anomalous bright contrast in the specimens containing dense dislocation slip planes, swept by moving dislocations was analysed. It is shown that the bright EBIC contrast outside the Schottky barrier is related to electrical activity of the extended defects generated in the slip plane by moving dislocations and thus, the slip plane acts as extended barrier separating excess carriers.

Residual strain profiles have been experimentally and theoretically compared between the two different growth techniques preparing GaAs substrates. One is the vertical boat (VB) technique and the other is the liquid-encapsulated Czochralski technique. It is found from the experimental observations that the residual strain profile of VB substrate is simple bowl-shaped, in which the residual strain value is high near the peripheral region, while the residual strain profile of LEC substrate is more complex and fourfold-symmetrical, in which the residual strain value is high in the inner regions as well as near the peripheral regions. In order to explain this experimental observation, we have estimated the thermal stress caused during the crystal growth by computer analysis. Thermal stress during VB growth is dominantly caused near the solid-liquid interface. On the other hand, strong thermal stress is caused during LEC growth both near the surface of boric oxide encapsulant and near the solid-liquid interface. It is therefore concluded that the observed difference of residual strain profiles may be coming mainly from the temperature profile difference between VB and LEC techniques.

We present an optical technique based on absorption measurements for the determination of the charge carrier concentration and its lateral distribution in n-type doped GaAs wafers. Calibration plots were determined in the charge carrier concentration range of 3 × 1017 m−3... 1 × 1018 cm−3 (range of trust up to 3 × 1018  cm−3) which is technically relevant for applications of GaAs wafers as substrate for laser and light emitting diodes. The error of the optical technique is in the range of 10% ... 15% and is comparable to electrical Hall measurements. The sensitivity of the setup, i.e. smallest detectable variation of doping (and hence charge carrier) concentration, is less than 1% in an area of 5 × 5 mm2 and about 20% across the 3 inch area. Absorption mappings of the charge carrier and hence doping homogeneity are presented for n-type GaAs:Si and GaAs:Te.

The EL2 as the most important intrinsic defect in semi-insulating GaAs was already deeply studied in the past. All investigation methods applied so far to semi-insulating GaAs explore the entire depth of the sample and are therefore not suitable to analyse e.g. influences of surface treatments. In this work the detection of EL2 in the surface of samples by the application of microwave detected photo induced current transient spectroscopy will be presented. A correlation between height and sign of the signals and the concentration of acceptors, furthermore of the compensation ratio of the EL2, the position of the Fermi level as well as the specific resistivity was found. The results can be simulated by solving rate equations for the measurement process.

Preferential etching is a simple and fast technique to evaluate the structural perfection of a single-crystalline material. In the area of defects, the etching rate of preferential etchants are different, so either hillocks or pits (etch-pits) appear. But most of the etching solutions reveal the defects only in thick layers or bulk materials, and often they are very specific for each material. Hence an appropriate etchant based on the Schimmel solution was developed by us for thin layer investigation. This modified Schimmel solution contains 55 Vol% CrO3 (0.4 M) and 45 Vol% HF (49%). The etch rate of this solution depends on the Ge content and on the degree of relaxation R. For the investigated thin Si$_{1-x}$Gex-heterolayers (x = 0.3–0.5) this solution provides an excellent controllable etch rate (0.12–0.48 µm/min), and shows a good capability of etch pit revealing, so the elucidation of countable etch-pits occurs. We implemented also a method for defect revealing based on the electrochemical capacitance voltage system. The determination of the etch pit density is performed by optical microscopy images (inverted dark-field and differential interference contrast) and by atomic force microscopy.