Albert Kwasniewski

High-precision absolute lattice parameter determination of SrTiO3, DyScO3 and NdGaO3 single crystals

The lattice parameters of three perovskite-related oxides have been measured with high precision at room temperature. An accuracy of the order of 10(-5) has been achieved by applying a sophisticated high-resolution X-ray diffraction technique which is based on the modified Bond method. The results on cubic SrTiO(3) [a = 3.905268 (98) Å], orthorhombic DyScO(3) [a = 5.442417 (54), b = 5.719357 (52) and c = 7.904326 (98) Å], and orthorhombic NdGaO(3) [a = 5.428410 (54), b = 5.498407 (55) and c = 7.708878 (95) Å] are discussed in view of possible systematic errors as well as non-stoichiometry in the crystals.

Phase-matching properties of BaGa4S7 and BaGa4Se7: Wide-bandgap nonlinear crystals for the mid-infrared

Biaxial BaGa4S7 and BaGa4Se7 crystals transparent in the mid-IR have been grown by the Bridgman–Stockbarger technique in sufficiently large sizes and with good optical quality to measure the refractive indices and analyze phase-matching properties. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Homo- and heteroepitaxial growth of Sn-doped β-Ga2O3 layers by MOVPE

Layers of β-Ga2O3in situ doped with Sn were grown on Al2O3 (0001) and native β-Ga2O3 (100) substrates by metal organic vapor phase epitaxy. Homoepitaxial growth of good-quality Sn-doped β-Ga2O3 layers with rocking curve values comparable to that of Czochralski-grown β-Ga2O3 substrates was attained. Sn incorporation in a wide range of concentrations (from 1017 to 1019 cm−3) was achieved without disturbing the crystallinity of the material grown. The interplay between deposition conditions and structural and electrical properties of the layers was studied. The Ga vacancy-related defects and the residual carbon from Ga-containing organic precursor carbon-related complexes have been revealed as acceptors compensating for intentionally introduced Sn donors. The advantage of employment of the melt-grown β-Ga2O3 crystals as homo-substrates for deposition of good-quality β-Ga2O3 layers is demonstrated. For the first time, n-type homoepitaxial semiconducting β-Ga2O3 layers were attained by MOVPE. The good quality of the epilayers was elucidated through HR-XRD measurements and a FWHM of the rocking curve of the (100) peak of 43 arcsec was obtained, which was comparable to those of the Czochralski-grown β-Ga2O3 substrates, demonstrating similar dislocation densities for epilayers and substrates.

Preparation of Bulk AlN Seeds by Spontaneous Nucleation of Freestanding Crystals

Freestanding AlN single crystals are grown in a RF-heated furnace by physical vapor transport (PVT). Three different growth regimes with growth temperatures between 2080–2200°C result in different crystal habits and very high structural quality. The Rocking curves show FWHM < 21 arcsec in the 0002 and 100 Reflection on the as-grown facets. Isometric AlN crystals with sizes up to 10 × 10 × 12mm3 show a zonar structure consisting of a yellowish core area which is grown on the N-polar (000) facet and a nearly colorless edge region grown on prismatic {100} facets. In the two growth zones nearly the same C concentrations but different amounts of O and Si are measured by secondary ion mass spectrometry (SIMS). The yellowish core area show a very low defect density (EPD ≤ 100 cm−2) and a higher deep UV transparency compared to the edge region.

Strain-induced phase transitions in epitaxial NaNbO3 thin films grown by metal–organic chemical vapour deposition

Epitaxially strained NaNbO3 films were grown by liquid-delivery spin metal–organic chemical vapour deposition on several oxide substrates, inducing tensile and compressive lattice strain. High-resolution X-ray diffraction measurements reveal that coherently grown compressively strained NaNbO3 films on NdGaO3 exhibit the orthorhombic c phase. With increasing in-plane strain a first structural phase transition to the monoclinic r phase and, further on, for films grown under tensile strain on rare earth scandates, a second phase transition to the aa phase, are observed. Our results are in good agreement with the pathway of phase transitions predicted by Dieguez, Rabe & Vanderbilt [Phys. Rev. B, (2005), 72, 144101] for NaNbO3 films.

X‐ray diffraction from nonperiodic layered structures with correlations: analytical calculation and experiment on mixed Aurivillius films

X-ray diffraction from films consisting of layers with different thicknesses, structures and chemical contents is analysed. The disorder is described by probabilities for different sequences of layers. Closed analytical expressions for the diffracted X-ray intensity are obtained when the layers form a stationary Markov chain. The proposed model is applied to the diffraction data from epitaxial sodium bismuth titanate thin films with Aurivillius structure possessing such one-dimensional disorder. In this case, the disorder is caused by a random stacking of three and four perovskite units separated by bismuth oxide interlayers. The results of analytical calculations are in good agreement with the experimental data and indicate that the incorporation of sodium in the Bi(4)Ti(3)O(12) phase causes the formation of a fourth perovskite unit.

BaGa 4 S 7 : wide-bandgap phase-matchable nonlinear crystal for the mid-infrared

We report measurements of the transparency, nonlinear coefficients and damage threshold of BaGa4S7 grown by the Bridgman-Stockbarger technique. We also present calculations showing that this crystal is phase-matchable for down conversion into the mid-IR starting from a pump wavelength of 1064 nm.

PbIn 6 Te 10 : new nonlinear crystal for three-wave interactions with transmission extending from 1.7 to 25 µm

We have grown single crystals of PbIn6Te10, with clear transparency from 3 to 20 µm, and showed that this new nonlinear material possesses sufficient birefringence for phase-matching of three-wave parametric interactions and a nonlinear coefficient of 51 pm/V.

Influence of oxygen partial pressure on SrTiO3 bulk crystal growth from non-stoichiometric melts

Cylindrical SrTiO3 single crystals with diameters and lengths exceeding one inch were grown from non-stoichiometric melts below 1800 °C using the high temperature top-seeded solution growth (TSSG) method. Despite the large crystal diameter the quality has been improved compared to Verneuil grown crystals. Typical etch pit density (EPD) values are in the range between 2 × 104 and 2 × 105 cm−2 for bulk crystals pulled in the direction and using seeds with EPD values of 5 × 105 cm−2. So far pulling SrTiO3 crystals from the melt suffers from growth instabilities like foot formation and subsequent spiraling. To avoid them an effective heat transport via the crystal is indispensable. Especially at elevated temperatures it requires a high optical transparency in the infrared region. In this paper we report the correlation between oxygen partial pressure, composition, IR-transmittance and coloration of the crystals. The growth at a sufficiently high oxygen partial pressure leads to an increase in the optical transparency of the crystals and can thereby suppress foot or spiral formation.

Growth of SrTiO3 bulk single crystals using edge-defined film-fed growth and the Czochralski methods

Cylindrical SrTiO3 bulk single crystals with diameters of about 15 mm and lengths between 13 and 50 mm were grown from stoichiometric melts by the edge-defined film fed growth (EFG) method. Typical average etch pit density values are in the range of 1.7–2.0 × 105 cm−2. Rocking curve measurements revealed FWHM values between 28′′ and 41′′. Suitable conditions for the growth of puck-shaped single crystals were also found for the Czochralski (Cz) method. However, the structural quality was lower as compared to crystals grown by the EFG method. So far pulling SrTiO3 crystals from the melt using the Czochralski method suffered from growth instabilities like diameter fluctuation, foot formation and subsequent spiraling immediately after the seeding stage. We achieved crystals with diameters up to 42 mm and lengths of 15 mm.