The Mn/ZnO(0001) system was investigated by synchrotron radiation photoemission. The Mn/ZnO interface with 4 ML of manganese deposited onto the ZnO surface was annealed up to 500ºC. No Mn capping layer was found at the surface after annealing as was confirmed by scanning Auger spectroscopy experiment. We used a resonant photoemission to extract the Mn3d partial density of states in photoemission spectra. The Mn3d states contribute to the electronic structure of the system within 10 eV of the Fermi level. They show three features: a main peak at 3.8-4.5 eV, a valence structure at the top of the valence band (1-3 eV), and a broad satellite situated between 5.5 and 9 eV below E_F. The satellite/main branching ratio was determined to be 0.43, which is a fingerprint of strong hybridization between the Mn3d electrons and the valence band of the crystal. The hybridization effect in Zn_{1-x} Mn_xO surface alloy is comparable to Zn_{1-x}Mn_xS and much higher than in Zn_{1-x}Mn_xSe, Zn_{1-x}Mn_xTe, and Ga_{1-x}Mn_xAs semimagnetic compounds.
Evolution of arsenic and phosphorus during heat treatment of unprotected and encapsulated Au, AuZn and AuGeNi contacts on GaAs and InP has been examined and correlated with their ohmic behavior.
Reactively sputtered TiN films were evaluated as annealing cap improving the formation of Au(Zn) ohmic contact and as antidiffusion barrier protecting contact metallization and underlying GaAs against reaction with Au overlayers.
Low resistance (Au)GeNi ohmic contacts to n-GaAs with smooth morphology and restricted penetration into the substrate have been fabricated. Rapid thermally nitrided tungsten has been demonstrated to be an effective capping layer during the contact processing.
In this study the capacitance-voltage (C-V) and deep level transient spectroscopy measurements have been performed on ZnTe (p-type)-Ti/Al Schottky diodes containing a layer of CdTe self-assembled quantum dots and on the reference diodes without dots for comparison. Both kinds of investigated samples were grown by molecular beam epitaxy technique. The dots were formed during the Stransky-Krastanov growth mode. Comparison of the C-V and deep level transient spectroscopy results obtained for both samples allows us to conclude that the 0.26 eV trap observed exclusively for the QD sample can be assigned to some defects in a wetting layer or CdTe/ZnTe interface.
The electrical properties of the CdTe/ZnTe quantum dot system have been analyzed to identify deep-level defects related with the presence of quantum dots. The capacitance-voltage (C-V) and deep level transient spectroscopy measurements were used to investigate the samples. A reference ZnTe sample (without dots) was also studied for comparison. Both samples were grown by molecular beam epitaxy technique on the n-type GaAs substrate. The quantum dots were formed by a Zn-induced reorganization of a thin CdTe layer. The presence of quantum dot formation was confirmed by micro-photoluminescence measurements. The deep level transient spectra for both samples are complex. In order to characterize individual contributions to the deep level transient spectra the latter have been simulated by separated Gaussian components [1]. The results of the deep level transient spectroscopy measurements yield the conclusion that the same defects are present in both materials but there is an increased concentration of the defects in the quantum dot structures. No deep level associated directly with the quantum dot confinement has been identified.
Interfacial reactions between GaSb and Au were studied by Rutherford backscattering, X-ray diffraction, and cross-sectional transmission electron microscopy. Evaluation of the extent to which the GaSb substrate decomposes was of primary concern. The results give evidence that the reaction takes place even at temperatures as low as 180°C. High reactivity of gold towards GaSb revealed by this study demonstrates that Au-based metallization is not a good candidate for device quality ohmic contacts to GaSb-based devices.
A study is made of surface preparation, metallization, patterning and dielectric deposition with the aim of developing process technology for GaSb-based photonic devices.
Ni/Si-based contact schemes based on the solid-phase regrowth process have been developed to form low-resistance ohmic contacts to GaN with a minimum contact resistivity of 1×10^{-3} Ωcm^{2} and ≈1×10^{-2} Ωcm^{2} to GaN:Si (n ≈ 2×10^{17} cm^{-3}) and GaN:Mg (p ≈ 3×10^{17} cm^{-3}). The solid-phase regrowth process responsible for the ohmic contact formation was studied using X-ray diffraction, secondary ion mass spectrometry and Rutherford backscattering spectrometry.
The interaction between CdTe and In during the formation of an ohmic contact has been investigated. Emphasis is placed on the study of the effect of thermally induced sublimation of cadmium on electrical properties of contacts. Presented results prove the effectiveness of cap annealing and rapid thermal processing in fabrication of improved ohmic contacts with limited Cd losses during the contacting procedure.
Monocrystalline films of zinc oxide were grown at 300C by atomic layer deposition. ZnO layers were grown on various substrates like ZnO bulk crystal, GaN, SiC and Al_2O_3. Electrical properties of the films depend on structural quality. Structural quality, surface morphology and optical properties of ZnO films were characterized using X-ray diffraction, scanning electron microscopy, and photoluminescence, respectively. High resolution X-ray diffraction spectra show that the rocking curve FWHM of the symmetrical 00.2 reflection equals to 0.058° and 0.009° for ZnO deposited on a gallium nitride template and a zinc oxide substrate, respectively. In low temperature photoluminescence sharp excitonic lines in the band-edge region with a FWHM equal to 4 meV, 5 meV and 6 meV, for zinc oxide deposited on gallium nitride, zinc oxide and sapphire substrate, respectively.
We present our research on fabrication and structural and transport characterization of ultrathin superconducting NbN layers deposited on both single-crystal Al_2O_3 and Si wafers, and SiO_2 and Si_3N_4 buffer layers grown directly on Si wafers. The thicknesses of our films varied from 6 nm to 50 nm and they were grown using reactive RF magnetron sputtering on substrates maintained at the temperature 850°C. We have performed extensive morphology characterization of our films using the X-ray diffraction method and atomic force microscopy, and related the results to the type of the substrate used for the film deposition. Our transport measurements showed that even the thinnest, 6 nm thick NbN films had the superconducting critical temperature of 10-12 K, which was increased to 14 K for thicker films.
We report fabrication and characterization of ultrathin NbN and NbTiN films designed for superconducting photodetectors. Our NbN and NbTiN films were deposited on Al_2O_3 and Si single-crystal wafers by a high-temperature, reactive magnetron sputtering method and, subsequently, annealed at 1000°C. The best, 18 nm thick NbN films deposited on sapphire exhibited the critical temperature of 15.0 K and the critical current density as high as ≈ 8 × 10^6 A/cm^2 at 4.8 K.
Electrical properties of RF magnetron sputtered p-NiO films were characterized after fabrication and after gamma irradiations using ^{137}Cs and ^{60}Co sources. Electrical parameters are obtained from the Hall measurements, impedance spectroscopy and C-V measurement of n-Si/p-NiO junction diodes. The results show that resistivity of the NiO film is gradually increased following after sequential irradiation processes because of the decrease in holes' concentration. Hole concentration of a NiO film decreases from the original value of 4.36 × 10^{16} cm^{-3} to 2.86 × 10^{16} cm^{-3} after ^{137}Cs γ irradiation with doses of 10 Gy. In the case of γ irradiation from ^{60}Co source, hole concentration of the film decreases from 6.3 × 10^{16}/cm^3 to 4.1 × 10^{16}/cm^3 and to 2.9 × 10^{16}/cm^3 after successive expositions with a dose of 20 Gy.
JavaScript is turned off in your web browser. Turn it on to take full advantage of this site, then refresh the page.