Excess Zn Atoms Research Articles

Heterogeneous in-situ nanostructure contributes to the thermoelectric performance of Zn4Sb3

Single-phase Zn4Sb3 and ZnSb-containing samples were prepared by Plasma Activated Sintering. An abrupt decrease of thermal conductivity was found at about 400 K, which is attributed to the microstructure change of Zn4Sb3. Nanoscale inclusions and compositional inhomogeneities were found in Zn4Sb3 sample at 473 K by high-resolution transmission electron microscopy. The phonon scattering is enhanced by increasing grain boundaries and chaotic structure, which reduces the thermal conductivity and increases the thermoelectric performance of Zn4Sb3 at elevated temperature. The Rietveld refinement results show that large ZnSb grains in ZnSb-containing samples will accommodate excess Zn atoms, and then reduce thermoelectric performance.

Effect of elevated annealing temperature on the microstructure and nano-hardness of ZnO films deposited by the sol-gel process

ZnO films deposited on Si substrates by the sol-gel process were characterized by transmission electron microscopy and energy dispersive X-ray spectroscopy to investigate the effect of annealing temperature (550°C and 800°C) on their microstructures and compositions. When the ZnO film was annealed at a temperature of 800°C, excess Zn atoms was formed in the ZnO film due to the thermal decomposition of ZnO into Zn and O atoms, creating a Zn/ZnO composite film. It was proposed that the excess Zn atoms in the Zn/ZnO composite film may serve to improve the resistance to dislocation motion within the ZnO film, thus increasing the strength of the film. Nanoindentation tests confirmed that the high annealing temperature was beneficial to increase the hardness of the ZnO film.

Reduction of In Composition in Heavily Zn-Doped InAlGaAs Layers Grown at Low Temperature by Metalorganic Chemical Vapor Deposition

Growth of heavily Zn-doped InAlGaAs at low temperature (560 °C) by metalorganic chemical vapor deposition (MOCVD) is investigated. The lattice constant contracts and the growth rate decreases with increasing dithylzinc (DEZn) flow rate. To clarify the reason, the growth rates of InAs, AlAs, and GaAs components are examined. The growth rates of AlAs and GaAs components are almost constant; only that of InAs dramatically decreases when the DEZn flow increases. This indicates that the incorporation of In is suppressed by the DEZn supply. The doping behavior during the growth is well fit by the surface adsorption-trapping model, which suggests that excess Zn atoms on the growth surface induce the reduction of the InAs component.

Highly conductive, undoped ZnO thin films deposited by electron-cyclotron-resonance plasma sputtering on silica glass substrate

The electrical and optical properties of undoped ZnO films deposited by electron cyclotron resonance (ECR) plasma sputtering at room temperature were characterized. The lowest resistivity we achieved was 2.6 × 10 − 3 Ωcm with optical transmittance at visible wavelengths higher than 85%. The X-ray diffraction (002) peak was weak and the rocking curve was asymmetrical, indicating that oxygen vacancies prevented large crystalline domains from forming. At low argon-sputtering-gas pressure, carrier concentration and Hall mobility increased with increasing argon pressure. When the optimum pressure (40 mPa) was exceeded, however, Hall mobility and optical transmittance were severely reduced, which indicated that excess Zn atoms were populated at the interstitials of the network. Admitting only 0.67 mPa of O 2 gas during deposition deteriorated resistivity over 1 MΩcm due to high excitation efficiency in the ECR plasma. Deposition under a higher magnetic field produced lower resistivities.

Effects of UV light irradiation and excess Zn addition on ZnO:Al film properties in sputtering process

Effects of UV light irradiation and excess Zn atoms in the film preparation of ZnO:Al film by sputtering were examined. When a glass substrate was irradiated by UV light of a 0.5-kW Hg lamp, film resistivity decreased to 70% of the resistivity of the film deposited on the initial non-irradiated substrate. Increases of both carrier concentration and Hall mobility were observed. This was due to the atomic excitation of depositing Zn or O atoms, not to the thermal effect through UV irradiation. An additional supply of Zn during the sputtering of ZnO:Al (2 wt%) target decreased the film resistivity, and carrier concentration increased drastically at a substrate temperature of 250°C. This was due to the improvement of film crystallinity by the addition of Zn atoms.

Crystallographic microstructure and electrical characteristics of Au/Pt/Ti/Ni ohmic contacts on p-type (001) ZnTe layers

The crystallographic microstructure and electrical characteristics of Au/Pt/Ti/Ni ohmic contacts on p-type (001) ZnTe layers are investigated as a function of annealing temperature, by using the transmission line model method, cross-sectional transmission electron microscopy, and Auger electron spectroscopy. The specific contact resistance decreases when the annealing temperature is increased and reaches a minimum at 300 °C. A minimum value of 1.1×10−6 Ω cm2 is obtained for a hole concentration of 3×1019 cm−3. The epitaxial NiTe2 that formed at the metal/semiconductor interface due to annealing is considered to play an important role in lowering the contact resistance. The excess Zn atoms created by the reaction between Ni and ZnTe are found to diffuse upward and to segregate at the Pt/Ni interface. A contact stability test performed at 102 °C suggests that these ohmic contact structures are stable even under high-current injection.

Preparation of conductive ZnO:Al films by a facing target system with a strong magnetic field

Transparent conductive ZnO:Al films were prepared in Ar gas by a planar magnetron sputtering system with facing targets, where strong internal magnets were contained in target holders to confine the plasma between the targets. A film resistivity of 4 × 10−4 Ω cm was attained at a substrate temperature of 200 dgC. However, the film resistivity increased with increasing substrate temperature, due to a decrease of the carrier concentration. The reason for this phenomenon was the decrease of Zn donors in the film as native donors or an increase of Zn defects. When excess Zn atoms were supplied during film growth, a low resistivity of 2 × 10−4 Ω cm was obtained even at a substrate temperature of 250 °C.

Control of preferred orientation for ZnO x films: control of self-texture

We tried to control preferred orientation of ZnO x films deposited by radio frequency (RF) magnetron sputtering, and to make the growth mechanisms clear. Zinc oxide has tetrahedral coordinates caused by sp 3 hybridized orbits, and the (0001) plane has the lowest surface free energy. Therefore, the film grows with strong (0001) preferred orientation even on glass. Considering the formation of tetrahedral coordination in the vapor phase and the deposition rate, however, we succeeded to control the preferred orientation of ZnO x films on glass. The (112̄0) textured film was obtained under sputtering gas composition which deteriorates the formation of tetrahedral coordination in the vapor phase and the high deposition rate. Formation of each texture is strongly related to the formation of tetrahedral coordination in the vapor phase and on the substrate during sputtering. Therefore, (112̄0) textured film had higher carrier concentration than that of the (0001) textured film caused by existing excess Zn atoms. Moreover, the growth mechanism with considering the density of surface energy, and the applications of the control for the epitaxial growth, are discussed.

酸素分圧制御水熱法による高純度ＺｎＯ単結晶の育成と評価

Zinc oxide single crystals of high purity have been grown by hydrothermal method under a partial pressure of oxygen, using a platinum-lined autoclave and ultra-pure reagents. The stoichiometry of grown crystals was investigated by employing coulometric technique to detect a small deviation in the stoichiometric constituent towards Zn1+xO. The concentration of the excess Zn atoms was accurately determined from 0.8 to 1.7 ppm and the electrical resistivity of the as-grown grown crystals measured as of the order of 108Ω-cm.

Hydrothermal growth and characterization of ZnO single crystals of high purity

Zinc oxide single crystals of high purity have been grown by the hydrothermal method under a partial pressure of oxygen, using a platinum-lined autoclave and ultra-pure reagents. The stoichiometry of the grown crystals was investigated by employing coulometric technique to detect a small deviation in the stoichiomtric constituent towards Zn 1+ x O. The concentration of the excess Zn atoms was accurately determined from 0.8 to 1.7 ppm and the electrical resistivity of the as-grown crystals was measured as of the order of 10 p8 Ω cm.

Hydrothermal Growth and Stoichiometric Assessment of ZnO Single Crystals of High Purity

Zinc oxide single crystals of high purity have been grown by the hydrothermal method adding a partial pressure of oxygen and using platinum-lined autoclave and ultra-pure nutrient reagents. The Stoichiometric assessment of the grown crystals was investigated by empoloying a coulometric analysis which was available for detecting a small deviation in the Stoichiometric constituent, such as Zn1+xO. The concentration of the excess Zn atoms was accurately determined from 0.8 to 1.7 ppm and the electrical resistivity of the as-grown crystals obtained in the order of 108Ω-cm.

GaAs1-xPx Light Emitting Diodes Produced by Zn Ion Implantation. II. Photoluminescence of p-Type Layers Formed by Ion Implantation and Diffusion

Photoluminescence of Zn implanted and Zn diffused GaAs1-xPx crystals was studied in order to clarify the reason for the extremely high luminescence efficiency of GaAs1-xPx diodes produced by ion implantation compared with diffused diodes. One of the reasons was found to be that the luminescence of the implanted diode occurs over a much wider region of the p-Type layer compared with that of the diffused diode. Moreover, the ion implantation method was found to be capable of producing a p-Type layer without the absorption band below the bandgap due to excess Zn atoms which reduce the luminescence efficiency of the diffused diode. From a photoluminescence study of the p-Type layer with low Zn concentration produced by using ion implantation, one of the main components of the electroluminescence of GaAs1-xPx diodes at low temperatures, which had not clearly been identified, was determined to be a Zn–Te donor-acceptor pair recombination.