Properties Of Bulk Single Crystals Research Articles

Experimental Hall electron mobility of bulk single crystals of transparent semiconducting oxides

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-Ga2O3, In2O3, ZnO, SnO2), ternary (ZnSnO3, BaSnO3, MgGa2O4, ZnGa2O4), and quaternary (Zn1−xMgxGa2O4, InGaZnO4) systems. Experimental outcome, covering over 200 samples measured at room temperature, revealed n-type conductivity of all TSOs with free electron concentrations (ne) between 5 × 1015 and 5 × 1020 cm−3 and Hall electron mobilities (μH) up to 240 cm2 V−1 s−1. The widest range of ne values was achieved for β-Ga2O3 and In2O3. The most electrically conducting bulk crystals are InGaZnO4 and ZnSnO3 with ne > 1020 cm−3 and μH > 100 cm2 V−1 s−1. The highest μH values > 200 cm2 V−1 s−1 were measured for SnO2, followed by BaSnO3 and In2O3 single crystals. In2O3, ZnO, ZnSnO3, and InGaZnO4 crystals were always conducting, while others could be turned into electrical insulators.Graphic abstract

MgGa2 O4 as a new wide bandgap transparent semiconducting oxide: growth and properties of bulk single crystals

Bulk MgGa2O4 single crystals with inverse spinel structure were grown from the melt by different methods. The degree of inversion could be changed by suitable annealing, which was confirmed by differential scanning calorimetry analysis and corresponding changes of the specific heat capacity. MgGa2O4 is thermally much more stable at high temperatures than β-Ga2O3 despite of a higher melting point of about 1930 °C and could be grown under a neutral atmosphere. Melt-grown MgGa2O4 crystals were found to be either electrical insulators or n-type semiconductors depending on the presence of oxygen in the growth atmosphere and the growth method applied. Growing the crystals in the presence of oxygen resulted in electrically insulating crystals. For as-grown and intentionally undoped semiconducting crystals, the free electron concentration was in the range of 1017–1018 cm−3, but the electron mobility was relatively low, just a few cm2V−1s−1. The free electron concentration remained at a level of 1018 cm−3 after annealing in a hydrogen-containing atmosphere at 600–900 °C for 10 h. On the other hand, annealing in an oxygen-containing atmosphere above 600 °C for 10–40 h turns the crystals from the semiconducting to the insulating state. The optical bandgap at room temperature amounts to about 4.9 eV. It decreases with temperature at a rate of 1.35 meV/K. Cathodoluminescence spectra of as-grown crystals show a dominant band at 362 nm. The melt-grown crystals have sufficient size and structural quality to be used as substrates for epitaxy.

Metastable resistivity ofLa0.8Ca0.2MnO3manganite thin films

Transport properties of ${\mathrm{La}}_{0.8}{\mathrm{Ca}}_{0.2}\mathrm{Mn}{\mathrm{O}}_{3}$ thin films 15 and $130\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ thick have been investigated and confronted with the properties of bulk single crystals of the same composition. It has been found that low-temperature resistivity of the films is sensitive to electric current and/or field treatment and thermal history of the sample. Thin films exhibit a variety of metastable resistive states and spontaneously evolve toward high-resistivity state in which the films exhibit highly nonlinear transport behavior at low temperatures. Nonlinear $V\text{\ensuremath{-}}I$ characteristics are well described by indirect tunneling model. The memory of the resistivity can be, at least partly, erased by a heat treatment at temperatures above the memory erasing temperature. The memory erasing temperature for thin films, $T=450\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, is significantly higher than that of single crystals. The results are interpreted in the context of strain driven phase separation. Coexistence of two ferromagnetic phases with different orbital orders and different conductivities is influenced by strains due to thermal cycling and current flow.

Structural, optical, and electrical properties of bulk single crystals of InAsxSb(1−x) grown by rotatory Bridgman method

Radially-homogeneous and single-phase InAsxSb(1−x) crystals, up to 5.0 at. % As concentration, have been grown using the rotatory Bridgman method. Single crystallinity has been confirmed by x-ray and electron diffraction studies. Infrared transmission spectra show a continuous decrease in optical energy gap with the increase of arsenic content in InSb. The measured values of mobility and carrier density at room temperature (for x=.05) are 5.6×104 cm2/V s and 2.04×1016 cm−3, respectively.

Phase diagram of the SrS–Ga 2S 3 system and its application to the single-crystal growth of SrGa 2S 4

Ce-doped SrGa 2S 4 compound is expected as a new host material of blue EL devices. However, the basic properties of bulk single crystals have not been fully clarified, since this compound has been mostly synthesized in the form of polycrystals or thin films. Here, we firstly present the pseudo-binary phase diagram of the SrS–Ga 2S 3 system constructed in accordance with our DTA data for single-crystal growth of SrGa 2S 4. It is shown that SrGa 2S 4 compound has a congruent melting point and a eutectic reaction in the side of excess of Ga 2S 3 concentration. On the basis of the phase diagram, single crystals of SrGa 2S 4 are grown using Ga 2S 3 as a self-flux in a horizontal Bridgman furnace. Colorless and transparent crystals having a typical size 2×2×2 mm 3 are obtained.

Synthesis and properties of nm-sized Sn 2P 2Se 6 single crystals embedded in photopolymeric host

The Sn 2P 2Se 6 single nanocrystallites embedded in a photopolymeric oligoetheracrylate host were manufactured. Structural and electrooptical investigations unambiguously show a possibility to obtain specimens which have properties similar to the properties of bulk single crystals. It was revealed that UV-hardening of the liquid photocompositions at temperatures allowing an incommensurate phase existence leads to an increase of the electrooptical coefficients. External electric field induces a partial crystallographic ordering of the embedded single crystallites of Sn 2P 2Se 6. After applying the electric fields of intensity higher than 16 kV/cm a saturation of the crystallographic ordering degree parameters as well as the electrooptical coefficients was observed. A temperature hysteresis of the electrooptical coefficient was also found.

Growth and Properties of Bulk Single Crystals of GaN

ABSTRACTIn this paper we review recent developments in the growth of bulk GaN crystals by a high-pressure, high-temperature method. We also provide information on various physical properties of bulk GaN material. Then, some preliminary results on the homoepitaxial growth of GaN are given. In the second part of this paper we discuss the following problems: the possible origin of the large free electron concentration in undoped GaN material, the parasitic effect of yellow luminescence and the nature of Zn- and Mg-acceptors.