Activation of phosphorous doping in high quality ZnO thin film grown on Yttria-stabilized zirconia (1 1 1) by thermal treatment

Phosphorous doped (P-doped) ZnO thin films are grown on c-sapphire and Yttria-stabilized zirconia (YSZ) (111) substrates by pulsed laser deposition. Post growth annealing is carried out to activate phosphorous to act as acceptor. The rocking curve of annealed P-doped ZnO films grown on YSZ (111) has full width at half maximum of 0.08°, more than two times narrower than that of the as-grown one. Neutral acceptor bound exciton (A⁰X) is observed from low temperature photoluminescence with estimated activation energy of 11.3 meV. Low carrier concentration of as-grown P-doped ZnO films indicated phosphorous doping creates acceptor states and/or reduced the oxygen vacancies. The carrier concentration of annealed samples is reduced by five order magnitudes from 3.21 × 10¹⁸ cm^− 3 to 1.21-8.19 × 10¹³ cm^− 3. At annealing temperature of 850 °C, the sample has the lowest carrier concentration and highest resistivity. This is an indication that the phosphorous in P-doped ZnO has been activated.     

Small pixel CZT detector for hard X-ray spectroscopy

A new small pixel cadmium zinc telluride (CZT) detector has been developed for hard X-ray spectroscopy. The X-ray performance of four detectors is presented and the detectors are analysed in terms of the energy resolution of each pixel. The detectors were made from CZT crystals grown by the travelling heater method (THM) bonded to a 20×20 application specific integrated circuit (ASIC) and data acquisition (DAQ) system. The detectors had an array of 20×20 pixels on a 250 μm pitch, with each pixel gold-stud bonded to an energy resolving circuit in the ASIC. The DAQ system digitised the ASIC output with 14 bit resolution, performing offset corrections and data storage to disc in real time at up to 40,000 frames per second. The detector geometry and ASIC design was optimised for X-ray spectroscopy up to 150 keV and made use of the small pixel effect to preferentially measure the electron signal. A ²⁴¹Am source was used to measure the spectroscopic performance and uniformity of the detectors. The average energy resolution (FWHM at 59.54 keV) of each pixel ranged from 1.09±0.46 to 1.50±0.57 keV across the four detectors. The detectors showed good spectral performance and uniform response over almost all pixels in the 20×20 array. A large area 80×80 pixel detector will be built that will utilise the scalable design of the ASIC and the large areas of monolithic spectroscopic grade THM grown CZT that are now available. The large area detector will have the same performance as that demonstrated here.     

Hot-wire chemical vapor deposition of silicon nanoparticles on fused silica

Silicon nanoparticles on fused silica have potential as recombination centers in infrared detectors due quantum confinement effects that result in a size dependent band gap. Growth on fused silica was realized by etching in HF, annealing under vacuum at 700-750 °C, and cooling to ambient temperature before ramping to the growth temperature of 600 °C. Silicon particles could not be grown in a thermal chemical vapor deposition (CVD) process with adequate size uniformity and density. Seeding fused silica with Si adatoms in a hot-wire chemical vapor deposition (HWCVD) process at a disilane pressure of 1.1 × 10^− 5 Pa followed by thermal CVD at a disilane pressure of 1.3 × 10^− 2 Pa, or direct HWCVD at a disilane pressure of 2.1 × 10^− 5 Pa led to acceptable size uniformity and density. Dangling bonds at the surface of the as-grown nanoparticle were passivated using atomic H formed by cracking H₂ over the HWCVD filament.     

Growth and electrical properties of mercury indium telluride single crystals

A novel photoelectronic single crystal, mercury indium telluride (MIT), has been successfully grown by using vertical Bridgman method (VB). The crystallinity, thermal and electrical properties of the MIT crystal were investigated. The results of X-ray rocking curve show that the as-grown MIT crystal has good crystal quality with the FWHM on (3 1 1) face of about 173 in. DSC measurement reveals that the Hg element is easy to solely evaporate from the compound when the temperature is higher than 387.9 °C in the open system. Hall measurements at room temperature show that the resistivity, carrier density and mobility of the MIT crystal were 4.79 × 10² Ω cm, 2.83 × 10¹³ cm⁻³ and 4.60 × 10² cm² V⁻¹ s⁻¹, respectively. The reduction of carrier mobility and the increase of the resistivity are related to the adding of In₂Te₃ into HgTe, which changes the energy band structure of the crystal.     

Synthesis and characterization of self-assembled ZnO nano-dots grown on SiNx/Si(001) substrates by radio frequency magnetron sputtering

This paper reports the synthesis and characterization of self-assembled ZnO nano-dots deposited on SiN_x/Si(001) substrates by radio frequency magnetron sputtering. The effect of the working pressure on the microstructure of the as-grown ZnO thin films was examined. At a working pressure of 6 × 10⁻³ Torr, a flat layered structure was dominant with a preferred orientation of the ZnO(0002) plane, while ZnO nano-structures were observed on the samples grown at 2 × 10⁻² Torr. This was attributed to the columnar growth that facilitated the nucleation of ZnO nano-structures on the growing surfaces. Hexagonal nano-pyramids were formed, which then transformed into nano-dots as the film became thicker. The ZnO nano-dots were uniform and well dispersed, exhibiting distinct photoluminescence spectra due to the quantum confinement effect.     

Dependence of optical and structural properties of ZnS and MgF2 multilayers as a function of the number of layers

In this paper, optical and structural properties of ZnS and MgF₂ multilayers grown by thermal evaporation are studied. Effects of annealing at different temperatures on samples with different number of layers are investigated. The maximum of reflection is shifted to different wavelengths, depending on the number of layers of the annealed samples. Using X-ray diffraction analysis, structural properties have been studied, and grain size and microstrain have been obtained by the Scherrer-Wilson formula, with grain sizes ranging from 10 nm to 22 nm for MgF₂ and from 0.9 nm to 210 nm for ZnS, and microstrain values from 2.5 × 10^− 3 to 3 × 10^− 3 for MgF₂, and from 1.2 × 10^− 3 to 2.6 × 10^− 3 for ZnS. Competition between crystallite size and microstrain is observed.     

Synthesis of K-doped p-type ZnO nanorods along (100) for ferroelectric and dielectric applications

Urchin-like p-type ZnO nanorods were grown along preferred (100) direction by low temperature solution technique and subjected to morphological, structural, Hall conductivity, dielectric and ferroelectric characterization. Hall voltage, bulk carrier density (hole) and mobility were found to be 0.058 V, 2.36 × 10¹⁹ cm⁻³ and 0.025 cm²/V s, respectively. In the temperature variation of the dielectric constant a phase transition at 343 K was observed at various frequencies. The piezoelectric charge coefficient (d₃₃) was found to be 1.60 pC/N. In the ferroelectric hysteresis loop studies, ZnO exhibited remnant polarization and coercive field at 0.083 µC/cm² and 3.86 kV/cm, respectively.     

Optical and ferromagnetic characteristics of Mn doped ZnO thin films grown by filtered cathodic vacuum arc technique

Mn doped ZnO (ZnO:Mn) thin films with ~ 10 at.% of Mn were grown on quartz substrates by filtered cathodic vacuum arc (FCVA) technique at low substrate temperature (≤ 200 °C). The influence of substrate temperature and oxygen flow rate on the optical, electrical and magnetic properties of the ZnO:Mn thin films was studied. Both room temperature ferromagnetism and ultraviolet photoluminescence were observed in all films. A maximum saturation moment of 2.9 × 10⁻²⁴ A m²/Mn can be achieved for the films grown in an optimum condition. This suggests that the fabrication of high-quality ZnO:Mn films by FCVA technique has the potential to realize efficient magneto-optic devices operating at ultraviolet regime.     

Surface planarization and masked ion-beam structuring of YBa2Cu3O7 thin films

Surface planarization and masked ion-beam structuring (MIBS) of high-T_c superconducting (HTS) YBa₂Cu₃O_7-δ (YBCO) thin films grown by pulsed-laser deposition (PLD) method is reported. Chemical-mechanical polishing, plasma etching, and oxygen annealing of YBCO films strongly reduce the particulate density (~ 10^-2 ×) and surface roughness (~ 10^-1 ×) of as-grown PLD layers. The resistivity, critical temperature T_c ≈ 90 K and critical current density J_c (77 K) > 1 MA/cm² of films are not deteriorated by the planarization procedure. The YBCO films are modified and patterned by irradiation with He⁺ ions of 75 keV energy. Superconducting tracks patterned by MIBS without removal of HTS material and, for comparison, by wet-chemical etching show same T_c and J_c(T) values. Different micro- and nano-patterns are produced in parallel on planarized films. The size of irradiated pattern depends on the mask employed for beam shaping and features smaller than 70 nm are achieved.     

Annealing behavior of single mode planar waveguide in YVO4 produced by He ion implantation

We report, for the first time to our knowledge, the formation of single mode planar waveguide in z-cut YVO₄ by 400 keV, 500 keV He ion implantation in fluence of 3 × 10¹⁶ ions/cm² at room temperature or at liquid nitrogen temperature (77 K). We investigated annealing behavior of the guiding mode and near-field image in the waveguide by prism-coupling method and end-face coupling method respectively. We found that the effective refractive index of the TE₀ mode was different before and after annealing for the samples implanted at room temperature, while, annealing had nearly no influence on the effective refractive index of the TE₀ mode of the samples implanted at liquid nitrogen temperature (77 K). After annealing at 600 K for 1 h, no guiding mode was observed in the sample implanted by 400 keV He ion in fluence of 3 × 10¹⁶ ions/cm² at room temperature. The Rutherford backscattering/channeling technique was used to investigate the damage reduction after annealing treatments. The minimum yield of the implanted, annealed sample was 5.43%. We reconstructed the refractive index profiles in the waveguide under different condition by applying intensity calculation method.     

Processing dependence of structural and physical properties of Mg2Ge thin films prepared by pulsed laser deposition

Magnesium germanide (Mg₂Ge) thin films were deposited on MgO (001) substrates using pulsed laser deposition technique. The films were deposited at various substrate temperatures, ranging from 300 to 600 °C. The effects of substrate temperature on structural, electrical and optical properties were studied. All the films, except the samples prepared at 300 °C, were polycrystalline with major diffraction from (200) plane. The highest electrical conductivity of 141.86 Ω^− 1 m^− 1 measured at room temperature was observed for the sample deposited at the highest temperature, with the corresponding charge carrier mobility and concentration of 2.62 cm² V/s and 8.66 × 10¹⁸ cm^− 3, respectively. The carrier concentration dependence of the optical absorption edge energy is accounted for by the Burstein-Moss shift. The variation of strain value may have also contributed to the change in bandgap energy. The reduction in direct bandgap energy was found to vary from 2.20 to 2.00 eV with increasing the deposition temperature.     

Surface analysis of argon-implanted zircalloy-2 and influence of bubble formation on the corrosion behavior

In order to simulate the irradiation damage, argon ions were implanted into zircalloy-2 alloy with a fluence ranging from 1×10¹⁶ to 1×10¹⁷ ions/cm², using an implanter at an extraction voltage of 190 kV, at liquid nitrogen temperature. Then the effect of argon ion implantation on the aqueous corrosion behavior of zircalloy-2 alloy was studied. The valence states of elements in the surface layer of the samples were analyzed by X-ray photoelectron spectroscopy (XPS). Transmission electron microscopy (TEM) was used to examine the microstructure of the argon-implanted samples. Glancing angle X-ray diffraction (GAXRD) was employed to examine the phase transformation due to the argon ion implantation. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of implanted zircalloy-2 alloy in a 1 M H₂SO₄ solution. It was found that the bubbles were formed on the surface of implanted samples; the bubbles grew larger with increasing argon fluence. The microstructure of argon-implanted samples changed from amorphous to partial amorphous, then to polycrystalline and finally to amorphous. The bubble forming and changing and microstructure changes affected the corrosion properties of implanted samples. Finally, the mechanism of the corrosion behavior of argon-implanted zircalloy-2 alloy is discussed.     

Fabrication of carbon nanoneedle and carbon nanowall mixture film with two-step growth method

A novel nano-carbon electron emitter film has been developed on a stainless steel substrate by a direct current plasma chemical vapor deposition system. Samples grown at temperatures of 900 °C and 1100 °C showed different surface morphologies. It is found that a two-step growth process established by combining these two temperature growths together is suitable for deposition of a high density emitter array film. The as-grown nano-carbon film indicates a carbon nanoneedle and carbon nanowall mixture film, where the needle array density is about 3 × 10⁷/cm². The I-V characteristic shows an emission current density of 228 mA/cm² at 2.5 V/μm, and the field emission current is stable, making it possibly suitable for developing field emission devices.     

Effects of periodicity and oxygen partial pressure on the crystallinity and dielectric property of artificial SrTiO3/BaTiO3 superlattices integrated on Si substrates by pulsed laser deposition method

Epitaxial SrTiO₃(STO)/BaTiO₃(BTO) artificial superlattices have been grown on TiN buffered Si (001) substrates by pulsed laser deposition method and the effects of stacking periodicity and processing oxygen partial pressure on their crystallinity and dielectric properties were studied. The crystal orientation, epitaxy nature, and microstructure of STO/BTO superlattices were investigated using X-ray diffraction and transmission electron microscopy. The TiN buffer layer and superlattice thin films were grown with cube-on-cube epitaxial orientation relationship of [110](001)_films∣∣[110](001)_TiN∣∣[110](001)_Si. The c-axis lattice parameter of the STO/BTO superlattice decreased from 0.412 nm to 0.406 nm with increasing oxygen partial pressure and the dielectric constants, measured at the frequency of 100 kHz at room temperature, of the superlattices with 2 nm/2 nm periodicity increased from 312 at 1 × 10^− 5 Torr to 596 at 1 × 10^− 3 Torr. The dielectric constants of superlattices grown at oxygen partial pressure of 1 × 10^− 3 Torr increased from 264 to 678 with decreasing periodicity of the superlattices from 10 nm/10 nm to 1 nm/1 nm.     

Growth and current-voltage characterization of ZnTe/CdTe heterojunctions

ZnTe layers have been grown on a (111) oriented CdTe single crystal substrate by vacuum thermal evaporation technique. The growth temperature was 180 °C at a base pressure of 10^− 4 N/m². The as-grown samples were investigated by X-ray diffraction. The pattern indicated a highly oriented crystallographic growth of ZnTe (111) layer on CdTe (111) substrate. The current-voltage characteristics in both forward and reverse biasing were carried out in the temperature range from 300 down to 200 K. The dark forward current curves were definitely of the diode type in the forward direction. This behavior can be understood as the barrier at the interface limits forward and reverse carrier flow across the junction, where the built-in potential could be developed. Series resistance due to the neutral region was estimated at approximately 320 Ω and the activation energy of the carriers was calculated and found to be 0.11 ± 0.03 eV. The reverse current shows negative resistance behavior at low voltage range.     

Effect of substrate temperatures on the electrical resistivity of thermally evaporated Mn thin films

Resistivity measurements have been performed on three samples of Mn thin films from 300 to 1.4 K using the van der Pauw four probe technique. The films were grown by thermal evaporation onto glass substrates held at 523, 323 and 77 K, respectively in a bell jar held at 6 × 10⁻⁶ Torr. The resistivity-temperature results of the three specimens reveal a variety of low temperature behaviours. A behaviour typical of the bulk α-Mn is obtained with the film grown at a substrate temperature of 523 K whilst with the film grown at a substrate temperature of 323 K, the resistivity tends to a saturation at low temperatures exhibiting a behaviour reminiscent of Kondo scattering. The resistivity-temperature behaviour of the sample held at a substrate temperature of 77 K may be regarded as typical of a metallic alloy glass with a negative temperature coefficient of resistivity at high temperatures and this turns to a T² dependence of resistivity at very low temperatures.     

Crystal growth and characterization of Cd0.8Mn0.2Te using Vertical Bridgman method

By Vertical Bridgman method, several Cd_0.8Mn_0.2Te (CdMnTe) ingots were grown. The structure and crystallinity of the ingots were evaluated by X-ray powder diffraction and double-crystal rocking curve measurement and etch pits density (EPD) measurement. The results showed a pure cubic zinc blende structure throughout the ingots with the full width at half maximum (FWHM) of 40-70 arcsec and EPD of (6-8) × 10⁴ cm⁻², indicating a high crystalline perfection. The Mn concentration distribution along the axial and radial direction of the ingots was measured by inductively coupled plasma atomic emission spectrometer (ICP-AES). The segregation coefficient k_eff for Mn along the axis of the ingots is determined to be 0.95, and the radial variation of Mn concentration is within 0.002. Current-voltage (I-V) measurement reveals that sputtered Au film can form good ohmic contact to CdMnTe wafer and all the wafers of the as-grown crystals have the resistivity within (1-4) × 10⁶ Ω cm. IR transmission measurement in the wave number region from 4000 to 1000 cm⁻¹ exhibits that the IR transmittance of CdMnTe wafers is 50-55%, which is close to the theoretical value.     

Magnetic flux pinning and flux jumps in polycrystalline MgB2

MgB₂ polycrystalline samples were fabricated under varying conditions of isostatic pressing in argon gas. The critical current densities (J_C) were determined through measurements of hysteresis loops, and the highest value of J_C at 10 K was 1.9 × 10⁴ A/cm² at 4.8 T. The depinning temperatures were measured at various magnetic fields using the vibrating reed technique. Flux jumps appeared below 7.4 K. The hysteresis loops were carefully examined to determine the temperature and magnetic field range where flux jumps appeared.     

Removal of stacking faults in Ge grown on Si through nanoscale openings in chemical SiO2

Nucleation and eventual coalescence of Ge islands, grown out of 5 to 7 nm diameter openings in chemical SiO₂ template and epitaxially registered to the underlying Si substrate, have been shown to generate a low density of threading dislocations (?10⁶ cm^− 2). This result compares favorably to a threading dislocation density exceeding 10⁸ cm^− 2 in Ge films grown directly on Si. However, the coalesced Ge film contains a relatively high density of stacking faults (5 × 10⁷ cm^− 2), and subsequent growth of GaAs leads to an adverse root-mean-square roughness of 36 nm and a reduced photoluminescence intensity at 20% compared to GaAs grown on Ge or GaAs substrates. Herein, we find that annealing the Ge islands at 1073 K for 30 min before their coalescence into a contiguous film completely removes the stacking faults. However, the anneal step undesirably desorbs any SiO₂ not covered by existing Ge islands. Further Ge growth results in a threading dislocation density of 5 × 10⁷ cm^− 2, but without any stacking faults. Threading dislocations are believed to result from the later Ge growth on the newly exposed Si where the SiO₂ has desorbed from areas uncovered by Ge islands. The morphology and photoluminescence intensity of GaAs grown on the annealed Ge is comparable to films grown on GaAs or Ge substrates. Despite this improvement, the GaAs films grown on the annealed Ge/Si exhibit a threading dislocation density of 2 × 10⁷ cm^− 2 and a minority carrier lifetime of 67 ps compared to 4 to 5 ns for GaAs on Ge or GaAs substrates. A second oxidation step after the high temperature anneal of the Ge islands is proposed to reconstitute the SiO₂ template and subsequently improve the quality of Ge film.     

Fabrication and dielectric property of ferroelectric PLZT films grown on metal foils

We have grown ferroelectric Pb_0.92La_0.08Zr_0.52Ti_0.48O₃ (PLZT) films on platinized silicon and LaNiO₃-buffered nickel substrates by chemical solution deposition using a sol-gel process based on acetic acid chemistry. The following measurements were obtained under zero-bias field: relative permittivity of ≈960 and dielectric loss of ≈0.04 on the PLZT film grown on Pt/Si substrates, and relative permittivity of ≈820 and dielectric loss of ≈0.06 on the PLZT film grown on LNO-buffered Ni substrates. In addition, a relative permittivity of 125 and dielectric loss of 0.02 were measured at room temperature under a high bias field of 1 × 10⁶ V/cm on PLZT deposited on LNO-buffered nickel substrate. Furthermore, a steady-state leakage current density of ≈8.1 × 10⁻⁹ A/cm² and mean breakdown field strength of 1.7 × 10⁶ V/cm were measured at room temperature. Finally, remanent polarization (P_r) of ≈2.0 × 10⁻⁵ C/cm², coercive electric field (E_c) of ≈3.4 × 10⁴ V/cm, and energy density of ≈45 J/cm³ were determined from room-temperature hysteresis loop measurements on PLZT/LNO/Ni film-on-foil capacitors with 250-μm-diameter platinum top electrodes.