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The dislocation evolution in a cross-section a-plane cut through a sublimation-grown aluminum nitride (AlN) crystal grown with low-temperature gradients and subsequent low thermal stress is investigated with different X-ray diffraction imaging methods. Exploiting the so-called weak-beam contrast using monochromatic X-rays in combination with suitable three-dimensional (3D) interpretation and reconstruction allows the identification of individual dislocations as well as tracing their progression in the crystal volume, even in the considerably strained interface region. It is particularly striking that the laterally grown crystal volume is dislocation-free. The dislocation densities in the seed and the bulk volume are similar (1 × 103cm–2), but while the dislocations in the seed are randomly arranged, the dislocations in the bulk volume show a uniform line shape, indicating a common mechanism of dislocation movement. Since the dislocation slings in the bulk do not lie in slip planes, it can be concluded that the lateral movement does not result from dislocation glide, but from impurity-driven climb of dislocations during growth. The absence of slip can be explained by the low-temperature gradients and the subsequent low thermal stress below the critical resolved shear stress (CRSS).

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We present the growth of bulk AlN crystals by physical vapor transport and the structural characterization by various X-ray techniques and defect-selective etching. Starting from native AlN seeds with 8 mm in diameter we show a fast increase of the crystal diameters with expansion angles of about 45°. Only two subsequent grown seeded crystals are required to reach crystals up to 34 mm in diameter. The threading dislocation density is below 104cm−2. The process outlines a shortcut path to industrially relevant AlN crystal diameters compared to all other published expansion processes for bulk AlN crystals so far.

In this article, the suitability of the etchants NaOH/KOH and Ba(OH)2for defect etching of metalorganic vapour‐phase epitaxy (MOVPE) grown AlN layers with a MgO‐assisted “drop method” is compared. Defect selectivity for the new etchant Ba(OH)2is confirmed by the local TEM analysis. Temperature dependence (420–500 °C) of etch pit sizes of a‐, mixed‐, and c‐type dislocations for both etchants are investigated by statistical evaluation of scanning electron microscopy (SEM) images. Additionally, the etch pit shape is analyzed for samples etched at 460 °C by atomic force microscopy (AFM) measurements. While a‐ and mixed‐type dislocations result in pits of comparable size and shape for both etchants, c‐type dislocations are already strongly etched with NaOH/KOH at low temperatures leading to over‐etching and MgO precipitation. Ba(OH)2,in contrast, generates smaller c‐type etch pits at low and medium etching temperatures and no MgO precipitates and is therefore preferable for drop etching. Ba(OH)2is introduced as a superior etchant for defect etching of metalorganic vapour‐phase epitaxy (MOVPE) grown AlN layers with an MgO‐assisted “drop method”. Unlike the standard etching agent NaOH/KOH, there are no MgO precipitations present in the temperature range 400–500 °C and the dislocation types (a, c, mixed) are easily distinguishable.

One of the most crucial defects for the device fabrication on silicon carbide (SiC) substrates are areas with low crystalline quality and micro-pipe clusters which can still occupy several percent of the area in commercial available 4H-substrates. These defects originate from the seed or are generated by modification changes during growth and can be easily detected under crossed polarizers. In this presentation the historic development at SiCrystal from Acheson material to wafers with 100mm diameter, state of the art micro-pipe density and excellent crystalline quality (FWHM < 20 arcsec) on whole area will be shown. Additionally the influence of carbon inclusions on surface quality and the present dislocation densities in 4H substrates will be discussed. While carbon inclusions were reduced to uncritical levels dislocation densities are still in the range of 104 cm-2. Therefore strategies for further reduction will be pointed out. Finally a resistivity limit (16 mΩcm) for stacking fault formation during annealing at 1150°C will be defined.

We report here an anisotropic increase in SiC bulk resistivity by annealing at 1150 °C, and discuss the implications for SiC devices. The increase in resistivity is resistivity dependent and can be (at least) partially reversed by a subsequent anneal at higher temperature. Ideal device performance is achievable with appropriate annealing steps during device processing.

Background: There have been scarce data on the distribution of clozapine concentrations in comparison with the recommended range (350–600 ng/ml) or their relationship with side effects among patients with treatment-resistant schizophrenia. Furthermore, no studies have assessed the association between side effects and overall exposure to the drug by calculating the 24-h area-under-curve (AUC).Methods: In- and outpatients with schizophrenia or schizoaffective disorder (ICD-10) who were receiving a stable dose of clozapine for ⩾2 weeks were included. Side effects were assessed using the Glasgow antipsychotic side-effects scale for clozapine (GASS-C). Using two collected plasma samples, plasma clozapine and norclozapine concentrations at peak and trough and their 24-h AUC were estimated using population pharmacokinetic models.Results: A total of 108 patients completed the study (mean ± SD age, 43.0 ± 10.1 years; clozapine dose, 357.5 ± 136.9 mg/day); 33 patients (30.6%) showed estimated trough concentrations of clozapine within the recommended range (350–600 ng/ml) whereas the concentrations were higher and lower than this range among 37 (43.5%) and 28 (25.9%) patients (%), respectively. There were no significant correlations between estimated peak or trough concentrations or 24-h AUC of both clozapine or norclozapine, and GASS-C total or individual scores. No significant differences were found between GASS-C total or individual item scores between the patients with estimated trough concentrations of clozapine of >600 ng/ml and the other subjects.Conclusion: The results suggest that clozapine or norclozapine concentrations are not linked directly to the extent of side effects experienced in clozapine-treated patients with treatment-resistant schizophrenia while the cross-sectional study design limits the interpretation of any causal relationships. These findings indicate that side effects associated with clozapine may occur at any dose or concentration.

We carried out investigations to elucidate the reasons for polytype changes in 4H. The aim was to sustain polytype stability throughout the entire process. The investigations were accompanied by studies on the formation of basal plane dislocations and their role as source for stacking faults. Several methods for the evaluation of material properties were applied to determine quality most precisely, e.g. KOH-defect-etching, optical microscopy, electron microscopy and X-ray-diffraction. We found out that several influences in growth conditions have to be controlled in a proper manner to achieve defect reduction. Based on these investigations we were able to improve our process and the crystal quality significantly. Best values for 3” 4H wafers show that EPD = 5x103 cm-2 , MPD < 0.1 cm-2 and FWHM-values < 15 arcsec can be achieved.

For several years the major focus of material issues in SiC substrates was laid on the reduction of macroscopic defects like polytype inclusions, low angle grain boundaries and micropipes. Since then significant improvements have been achieved and micropipe densities could be reduced to values below 1 cm-2. Nevertheless the fabrication of high quality substrates at high volume and low cost is still challenging. Therefore preconditions for reproducible process and quality control will be discussed. Since it is obvious that dislocations are the main reason for degradation in power devices the prevailing attention has also been shifted to that field of material research. Intense studies were utilized on dislocation and stacking fault formation during sublimation growth. For this reason we systematically varied crucial parameters of the crystal growth process and applied several specific characterization methods, e.g. KOH-defect-etching, electron microscopy and optical microscopy, to evaluate resulting material properties. The investigations were accompanied by failure analysis on devices of the Schottky-type. We found out that for the improvement of substrate quality emphasis has to be laid on the reduction of thermoelastic stress in the growing crystal. The results of numerical calculations enabled us to derive moderate growth conditions with reduced temperature gradients and correspondingly low defect concentration.

We review the development of a modified physical vapor transport (M-PVT) growth technique for the preparation of SiC single crystals which makes use of an additional gas pipe into the growth cell. While the gas phase composition is basically fixed in conventional physical vapor transport (PVT) growth by crucible design and temperature field, the gas inlet of the MPVT configuration allows the direct tuning of the gas phase composition for improved growth conditions. The phrase "additional" means that only small amounts of extra gases are supplied in order to fine-tune the gas phase composition. We discuss the experimental implementation of the extra gas pipe and present numerical simulations of temperature field and mass transport in the new growth configuration. The potential of the growth technique will be outlined by showing the improvements achieved for p-type doping of 4H-SiC with aluminum, i.e. [Al]=9⋅1019cm-3 and ρ<0.2Ωcm, and n-type doping of SiC with phosphorous, i.e. [P]=7.8⋅1017cm-3.

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