By differential thermal analysis, a concentration field suitable for the growth of Zr, Mg co-doped strontium hexagallate crystals was observed that corresponds well with known experimental results. ...It was shown that the melting point of doped crystal is ca. 60 K higher than that of undoped crystals. This higher melting points indicate hexagallate phase stabilization by Zr, Mg co-doping and increase the growth window of (Mg,Zr):SrGa
12
O
19
, compared to undoped SrGa
12
O
19
that grows from SrO–Ga
2
O
3
melts.
We provide a comparative study of basic electrical properties of bulk single crystals of transparent semiconducting oxides (TSOs) obtained directly from the melt (9 compounds) and from the gas phase ...(1 compound), including binary (β-Ga
2
O
3
, In
2
O
3
, ZnO, SnO
2
), ternary (ZnSnO
3
, BaSnO
3
, MgGa
2
O
4
, ZnGa
2
O
4
), and quaternary (Zn
1−x
Mg
x
Ga
2
O
4
, InGaZnO
4
) systems. Experimental outcome, covering over 200 samples measured at room temperature, revealed n-type conductivity of all TSOs with free electron concentrations (
n
e
) between 5 × 10
15
and 5 × 10
20
cm
−3
and Hall electron mobilities (
μ
H
) up to 240 cm
2
V
−1
s
−1
. The widest range of
n
e
values was achieved for β-Ga
2
O
3
and In
2
O
3
. The most electrically conducting bulk crystals are InGaZnO
4
and ZnSnO
3
with
n
e
> 10
20
cm
−3
and
μ
H
> 100 cm
2
V
−1
s
−1
. The highest
μ
H
values > 200 cm
2
V
−1
s
−1
were measured for SnO
2
, followed by BaSnO
3
and In
2
O
3
single crystals. In
2
O
3
, ZnO, ZnSnO
3
, and InGaZnO
4
crystals were always conducting, while others could be turned into electrical insulators.
Graphic abstract
The performance characteristics of optically pumped laser heterostructures emitting in the UV-C spectral range between 272 and 279 nm are investigated. The laser heterostructures were grown by ...metal-organic vapor phase epitaxy on (0001) planar AlN/sapphire, epitaxially laterally overgrown (ELO) AlN/sapphire, and bulk AlN substrates with threading dislocation densities ranging from 2×10 10 to 10 4 cm -2 . We found that the defect density strongly affects the laser performance. The lowest pulse threshold energy density of 50 mJ/cm 2 under resonant optical pumping condition was obtained for an AlGaN multiple quantum well laser grown pseudomorphically on low defect density bulk AlN substrate. Lasing was also observed for AlGaN MQW heterostructures grown on ELO AlN/sapphire templates. The laser emission in all lasers was TE polarized. However, no lasing was observed for heterostructures grown on high defect density AlN/sapphire.
Truly bulk ZnGa2O4 single crystals were obtained directly from the melt. High melting point of 1900 ± 20 °C and highly incongruent evaporation of the Zn- and Ga-containing species impose restrictions ...on growth conditions. The obtained crystals are characterized by a stoichiometric or near-stoichiometric composition with a normal spinel structure at room temperature and by a narrow full width at half maximum of the rocking curve of the 400 peak of (100)-oriented samples of 23 arcsec. ZnGa2O4 is a single crystalline spinel phase with the Ga/Zn atomic ratio up to about 2.17. Melt-grown ZnGa2O4 single crystals are thermally stable up to 1100 and 700 °C when subjected to annealing for 10 h in oxidizing and reducing atmospheres, respectively. The obtained ZnGa2O4 single crystals were either electrical insulators or n-type semiconductors/degenerate semiconductors depending on growth conditions and starting material composition. The as-grown semiconducting crystals had the resistivity, free electron concentration, and maximum Hall mobility of 0.002–0.1 Ωcm, 3 × 1018–9 × 1019 cm−3, and 107 cm2 V−1 s−1, respectively. The semiconducting crystals could be switched into the electrically insulating state by annealing in the presence of oxygen at temperatures ≥700 °C for at least several hours. The optical absorption edge is steep and originates at 275 nm, followed by full transparency in the visible and near infrared spectral regions. The optical bandgap gathered from the absorption coefficient is direct with a value of about 4.6 eV, close to that of β-Ga2O3. Additionally, with a lattice constant of a = 8.3336 Å, ZnGa2O4 may serve as a good lattice-matched substrate for magnetic Fe-based spinel films.
The thermal conductivity of AlN single crystals grown by physical vapor transport (PVT) and hydride vapor phase epitaxy (HVPE) was measured in the range of 30 to 325 K by the 3ω method. The measured ...room-temperature thermal conductivity ranged from 268 to 374 W m−1 K−1. Higher thermal conductivity correlated with higher transparency at 265 nm and lower total impurity levels.
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 $\mathrm{FWHM}< 21$ arcsec in the 0002 and $10\bar{1}0$ Reflection on the as-grown facets. Isometric AlN crystals with sizes up to $10\times 10\times 12$ mm 3 show a zonar structure consisting of a yellowish core area which is grown on the N-polar ($000\bar{1}$) facet and a nearly colorless edge region grown on prismatic $\{10\bar{1}0\}$ 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 ($\mathrm{EPD}\leq 100$ cm -2 ) and a higher deep UV transparency compared to the edge region.
Strontium titanate (SrTiO3), a well-established traditional perovskite substrate as well as a promising substrate crystal for the epitaxy of new advanced perovskite-type thin films, suffers from the ...unavailability in adequate quality for the latter. To improve the situation attempts have been made to grow SrTiO3 at moderate temperatures (<1535°C) well below the melting temperature and under low temperature gradients by the top-seeded solution growth method. Based on very special modifications of the growth conditions, virtually mosaicity-free SrTiO3 single crystals in the 1–2cm range were obtained. High crystalline quality was verified by defect selective etching, rocking curve measurements, energy dispersive Laue mappings and by synchrotron X-Ray diffraction topography. The production of virtually subgrain- and dislocation free substrate crystals is essential to considerably improve characteristics of SrTiO3 based SQUIDs, transistors or memory devices and to allow an in-depth analysis of intrinsic and extrinsic factors influencing the properties of epitaxially grown oxide heterostructures.
•The TSSG method is suitable to grow virtually mosaicity-free SrTiO3 single crystals.•Low temperature gradients allow defect minimized broadening of the crystal.•Low-stress wafer preparation is crucial to obtain superior SrTiO3 substrate crystals.
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