Determination of electrical types in the P-doped ZnO thin films by the control of ambient gas flow

Phosphorus (P)-doped ZnO thin films with amphoteric doping behavior were grown on c-sapphire substrates by radio frequency magnetron sputtering with various argon/oxygen gas ratios. Control of the electrical types in the P-doped ZnO films was achieved by varying the gas ratio without post-annealing. The P-doped ZnO films grown at a argon/oxygen ratio of 3/1 showed p-type conductivity with a hole concentration and hole mobility of 1.5 × 10¹⁷ cm⁻³ and 2.5 cm²/V s, respectively. X-ray diffraction showed that the ZnO (0 0 0 2) peak shifted to lower angle due to the positioning of P³⁻ ions with a larger ionic radius in the O²⁻ sites. This indicates that a p-type mechanism was due to the substitutional P_O. The low-temperature photoluminescence of the p-type ZnO films showed p-type related neutral acceptor-bound exciton emission. The p-ZnO/n-Si heterojunction light emitting diode showed typical rectification behavior, which confirmed the p-type characteristics of the ZnO films in the as-deposited status, despite the deep-level related electroluminescence emission.     

Pulsed laser deposition of Zr–N codoped <Emphasis Type="Italic">p</Emphasis>-type ZnO thin films

Present p-type ZnO films tend to exhibit high resistivity and low carrier concentration, and they revert to their natural n-type state within days after deposition. One approach to grow higher quality p-type ZnO is by codoping the ZnO during growth. This article describes recent results from the growth and characterization of Zr–N codoped p-type ZnO thin films by pulsed laser deposition (PLD) on (0001) sapphire substrates. For this work, both N-doped and Zr–N codoped p-type ZnO films were grown for comparison purposes at substrate temperatures ranging between 400 to 700 °C and N₂O background pressures between 10⁻⁵ to 10⁻² Torr. The carrier type and conduction were found to be very sensitive to substrate temperature and N₂O deposition pressure. P-type conduction was observed for films grown at pressures between 10⁻³ to 10⁻² Torr. The Zr–N codoped ZnO films grown at 550 °C in 1×10⁻³ Torr of N₂O show p-type conduction behavior with a very low resistivity of 0.89 Ω-cm, a carrier concentration of 5.0×10¹⁸ cm⁻³, and a Hall mobility of 1.4 cm² V⁻¹ s⁻¹. The structure, morphology and optical properties were also evaluated for both N-doped and Zr–N codoped ZnO films.     

Der Einfluß der freien Ladungsträger auf die optischen Konstanten des Bi2Se3 im Wellenlängengebiet von 2 bis 23 μm

The influence of free carriers on the optical constants of Bismuthtriselenide Bi₂Se₃ was investigated in the infrared (2–23 μm). The reflection and transmission ofn-type Bi₂Se₃ single crystals was measured at approximately 30, 80 and 300 °K. Up till now,p-type Bi₂Se₃ is not known. The dependence of the refraction index and the absorption constant on the wavelength was calculated from the results of the measurements. It was found that the optical constants strongly depend on the carrier concentration. The crystals were prepared according the bridgman method. They normally have a carrier concentration of about 10¹⁹ cm^?3, which can be diminished by annealing in Selenium vapour of various pressure up to 10¹⁸ cm^?3. Bismuthtriselenide is a degenerated semiconductor. We obtained for the optical energy band gap by extrapolation the value 0,21 eV. It increases with increasing carrier concentration. This is known as the Burstein-Moss-effect.     

Change of the electron effective mass in extremely heavily doped n-type Si obtained by ion implantation and laser annealing

Infrared optical properties of extremely heavily doped n-type Si, obtained by ion implantation and laser annealing, were studied. A new relation between free carrier effective mass (m¹) and carrier concentration (10¹⁹ ?5 × 10²¹cm^-3) was obtained. The value of m¹ increases significantly with the increase of carrier concentration, when carrier concentration exceeds 10²¹cm^-3. The result is discussed in relation to the occupation of electrons in a new valley of the conduction band.     

Minority carrier lifetime in highly doped Ge

The minority carrier lifetime is measured in p-type Ge up to a majority carrier concentration of 10¹⁹ cm⁻³ using the photoconductive effect and the photo-magneto-electric effect. A stronger than linear dependence of the reciprocal lifetime on the carrier density is observed. Therefrom, from the weak temperature-dependence, from previous work and from the comparison with Si-data, we conclude that the dominant recombination mechanism at high carrier concentrations is the phonon-assisted band to band Auger-recombination. A transition coefficient of about 10⁻³¹ cm⁶ sec⁻¹ is estimated.     

The observation of high concentrations of arsenic anti-site defects in electron irradiated n-type GaAs by X-band EPR

N-type GaAs doped with sulphur (2.8 × 10¹⁸ cm^-3) has been subjected to 2 MeV electron irradiation in stages at room temperature and examined by the EPR technique. When the free carrier absorption is first eliminated no EPR signal is detected. After further irradiation, the spectrum of the As anti-site defect appears, grows and subsequently saturates at a concentration of about 10¹⁸ cm^-3. The saturation concentration is about one third of [n] in most samples. The defects are stable on annealing to 500°C but are not observed in various irradiated p-type samples. It is suggested that grown-in defects such as [V_Ga-As_Ga-V_Ga] capture Ga interstitials during the irradiation and are thereby converted to the simpler anti-site defect.     

Enhancement of the electrical characteristics of indium–zinc tin-oxide thin-film transistors utilizing dual-channel layers

Thin film transistors (TFTs) with indium–zinc tin-oxide (IZTO) dual-channel layers were fabricated on heavily-doped p-type Si substrates by using a tilted dual-target radio-frequency magnetron sputtering system. The number of oxygen vacancies in the IZTO channel layer decreased with increasing oxygen partial pressure, resulting in a decrease in the conductivity. The threshold voltage (V_th) shifted toward positive gate-source voltage with increasing oxygen partial pressure for the growth of the IZTO layer because of a decrease in the carrier concentration. The V_th, the mobility, the on/off-current ratio, and the subthreshold swing of the dual-channel IZTO TFTs were 3.5 V, 7.1 cm²/V s, 1.3 V/decade, and 8.2 × 10⁶, respectively, which was enhanced by utilizing dual-channel layers consisting of a top channel deposited at a high oxygen partial pressure and a bottom channel deposited at a low oxygen partial pressure.     

Synthesis,electrical and optical properties of CuNdO2 compound

CuNdO₂, a p-type transparent conducting oxide has been synthesized by conventional solid-state reaction. The XRD and TEM results show that the pure delafossite phase is obtained, furthermore, the EDX results indicate the sample is obviously oxygen-rich. The p-type conduction of CuNdO₂ was confirmed by Hall and Seebeck measurements. Carrier concentration and mobility at room temperature are around 1.38×10¹⁷ cm^?3 and 1.24 cm²V^?1s^?1, respectively. On the other hand, the optical band gap of CuNdO₂ is estimated to be around 3.14 eV, which agrees well with the theoretical result predicted by the first-principle calculation.     

Fermi surface and metallic properties of graphite at high pressures

A potential of superconductivity of pure graphite has been theoretically examined. At normal pressure, the carrier concentration is too low to exhibit superconductivity. On applying pressure, the band dispersion along the c-axis is significantly enhanced, resulting in an increase in the carrier concentration; 10²⁰ cm^-3 at p=30 GPa. This is favorable to observe superconductivity. Accurate Fermi surfaces are illustrated: a new Fermi surface appears around K point at p=25 GPa.     

Formation of p-type ZnMgO thin films by In-N codoping method

In-N codoped ZnMgO films have been prepared on glass substrates by direct current reactive magnetron sputtering. The p-type conduction could be obtained in ZnMgO films by adjusting the N₂O partial pressures. The lowest resistivity was found to be 4.6 Ω cm for the p-type ZnMgO film deposited under an optimized N₂O partial pressure of 2.3 mTorr, with a Hall mobility of 1.4 cm²/V s and a hole concentration of 9.6 × 10¹⁷ cm⁻³ at room temperature. The films were of good crystal quality with a high c-axis orientation of wurtzite ZnO structure. The presence of In-N bonds was identified by X-ray photoelectron spectroscopy, which may enhance the nitrogen incorporation and respond for the realization of good p-type behavior in In-N codoped ZnMgO films. Furthermore, the ZnMgO-based p-n homojunction was fabricated by deposition of an In-doped n-type ZnMgO layer on an In-N codoped p-type ZnMgO layer. The p-n homostructural diode exhibits electrical rectification behavior of a typical p-n junction.     

Optoelectronic properties of Cu1−xPtxFeO2 (0 ≤ x ≤ 0.05) delafossite for p-type transparent conducting oxide

The samples of Cu_1−xPt_xFeO₂ (0 ≤ x ≤ 0.05) delafossite have been synthesized by solid-state reaction method to investigate their optical and electrical properties. The properties of electrical resistivity and Seebeck coefficient were measured in the high temperature ranging from 300 to 960 K, and the Hall effect and the optical properties were measured at room temperature. The obtained results of Seebeck showed the samples are p-type conductor. The optical properties at room temperature exhibited the samples are transparent visible light material with optical direct gap 3.45 eV. The low electrical resistivity, hole mobility and carrier density at room temperature displayed value ranging from 0.29 to 0.08 Ω cm, 1.8 to 8.6 cm²/V s and 1.56 × 10¹⁸ to 4.04 × 10¹⁹ cm⁻³, respectively. The temperature range for transparent visible light is below 820 K because the direct energy gap contains value above 3.1 eV. Consequently, the Cu_1−xPt_xFeO₂ delafossite enhance performance for materials of p-type transparent conducting oxide (TCO) with low electrical resistivity.     

Transmutation doping of GaAs by thermal neutrons

The electrical properties of GaAs have been modified by transmutation of about 1 × 10¹⁸ As atoms per cm³ to Se and 0.7 × 10¹⁸ Ga atoms per cm³ to Ge in a flux of thermal neutrons, followed by annealing at temperatures from 625 to 900°C. Enhancement of carrier concentration was not observed in n⁺ samples, although p and n^? material showed changes in carrier concentration of the expected magnitude.     

Anomalous mobility enhancement in Si doping superlattices

Enhanced Hall mobility has been measured in Si doping superlattices with pipi or nini doping profiles grown by molecular beam epitaxy. Although the carrier concentration is large, in the range of 10¹⁸cm⁻³, the mobility of holes in the pipi doping superlattice has the temperature dependence such as that expressed in the T^−2.2 law which is characteristic of high purity bulk crystals. The hole mobility is about twice that of high purity crystals, rising up to 40,000 cm²/V.s at about 30 K. In the case that p-type impurity concentration is comparable to n-type impurity concentration, no mobility enhancement is observed and the mobility is anomalously depressed. The mechanisms for drastical change in the mobility of doping superlattices have not yet been clarified.     

Evidences of defect contribution in magnetically ordered Sm-implanted GaN

Samarium (Sm) ions of 200 keV in energy were implanted into highly-resistive molecular-beam-epitaxy grown GaN thin films with a focused-ion-beam implanter at room temperature. The implantation doses range between 10¹⁴ and 10¹⁶ cm⁻². X-ray diffraction revealed Sm incorporation into GaN matrix without secondary phase. Raman-scattering spectroscopy identified impurity-independent defect-related oscillation modes. Slight decrease in band gap and significant reduction in transmittance were observed by optical transmission spectroscopy. Photoluminescence spectra showed emission peaks related to background p-type impurity. Ferromagnetic hysteresis loops were recorded from GaN implanted with highest Sm dose, and magnetic ordering was observed from Sm-implanted GaN with dose of and above 10¹⁵ cm⁻². The long-range magnetic ordering can be attributed to interaction of Sm ions through the implantation-induced Ga vacancy.     

Raman scattering investigations on Co-doped ZnO epitaxial films: Local vibration modes and defect associated ferromagnetism

Raman scattering spectroscopy has been performed on high quality Co-doped ZnO epitaxial films, which were grown on Al₂O₃ (0001) by oxygen-plasma assisted molecular beam epitaxy. Raman measurements revealed two local vibration modes (LVMs) at 723 and 699 cm⁻¹ due to the substitution of Co²⁺ in wurtzite ZnO lattice. The LVM at 723 cm⁻¹ is found to be an elemental sensitive vibration mode for Co substitution. The LVM at 699 cm⁻¹ can be attributed to enrichment of Co²⁺ bound with oxygen vacancy, the cobalt–oxygen vacancy–cobalt complexes, in Zn_1−xCo_xO films associated with ferromagnetism. The intensity of LVM at 699 cm⁻¹, as well as saturated magnetization, enhanced after the vacuum annealing and depressed after oxygen annealing.     

Structural and electrical properties of fluorine-doped zinc tin oxide thin films prepared by radio-frequency magnetron sputtering

Transparent and conductive thin films of fluorine doped zinc tin oxide (FZTO) were deposited on glass substrates by radio-frequency (RF) magnetron sputtering using a 30 wt% ZnO with 70 wt% SnO₂ ceramic targets. The F-doping was carried out by introducing a mixed gas of pure Ar, CF₄, and O₂ forming gas into the sputtering chamber while sputtering ZTO target. The effect of annealing temperature on the structural, electrical and optical performances of FZTO thin films has been studied. FZTO thin film annealed at 600 °C shows the decrease in resistivity 5.47 × 10⁻³ Ω cm, carrier concentration ∼10¹⁹ cm⁻³, mobility ∼20 cm² V⁻¹ s⁻¹ and an increase in optical band gap from 3.41 to 3.60 eV with increasing the annealing temperatures which is well explained by Burstein–Moss effect. The optical transmittance of FZTO films was higher than 80% in all specimens. Work function (ϕ) of the FZTO films increase from 3.80 eV to 4.10 eV through annealing and are largely dependent on the amounts of incorporated F. FZTO is a possible potential transparent conducting oxide (TCO) alternative for application in optoelectronics.     

Optimization of pulsed laser deposited ZnO thin-film growth parameters for thin-film transistors (TFT) application

In this work we present the optimization of zinc oxide (ZnO) film properties for a thin-film transistor (TFT) application. Thin films, 50±10 nm, of ZnO were deposited by Pulsed Laser Deposition (PLD) under a variety of growth conditions. The oxygen pressure, laser fluence, substrate temperature and annealing conditions were varied as a part of this study. Mobility and carrier concentration were the focus of the optimization. While room-temperature ZnO growths followed by air and oxygen annealing showed improvement in the (002) phase formation with a carrier concentration in the order of 10¹⁷–10¹⁸/cm³ with low mobility in the range of 0.01–0.1 cm²/V?s, a Hall mobility of 8 cm²/V?s and a carrier concentration of 5×10¹⁴/cm³ have been achieved on a relatively low temperature growth (250 °C) of ZnO. The low carrier concentration indicates that the number of defects have been reduced by a magnitude of nearly a 1000 as compared to the room-temperature annealed growths. Also, it was very clearly seen that for the (002) oriented films of ZnO a high mobility film is achieved.     

The Effects of Thermal Treatments on Microstructure Phosphorus-Doped ZnO Layers Grown by Thermal Evaporation

The ZnO films doped with 3 wt% phosphorus (P) were produced by activating phosphorus doped ZnO (ZnO:P) thin films in oxygen (O₂) ambient at 600°C for 30, 60, 90 and 120 min, respectively. As-deposited films doped with phosphorus are highly conductive and n type. All the films showed p-type conduction after annealing, in an O₂ ambient atmosphere. The activation energies of the phosphorus dopant in the p-type ZnO under O₂ ambient gases indicate that phosphorus substitution on the O site yielded a deep level in the gap. With a further increase of the annealed durations, the crystalline quality of the ZnO:P sample is degraded. The best p-type ZnO:P film deposited at 600°C for 30 min shows a resistivity of 1.85 Ω cm and a relatively high hole concentration of 5.1 × 10¹⁷cm^–3 at room temperature. The films exhibit a polycrystalline hexagonal wurtzite structure without preferred orientation. The mean grain sizes are calculated to be about 60, 72, 78, 85 and 90 nm for the p-type ZnO films prepared at 600°C for 30, 60, 90 and 120 min, respectively. Room temperature photoluminescence (PL) spectra of the ZnO film exhibit two emission bands — paramount excitonic ultraviolet (UV) emission and weak deep level visible emission. The excellent emission from the film annealed at 600°C for 30 min is attributed to the good crystalline quality of the p-type ZnO film and the low rate of formation of intrinsic defects at such short duration. The visible emission consists of two components in the green range.     

Electrical properties of Cd,Zn and S ion-implanted layers in GaAs

The electrical properties of cadmium, zinc, and sulfur ion-implanted layers in gallium arsenide have been measured by the van der Pauw-Hall technique. Ion implantation was performed with the substrates held at room temperature. The dependence of sheet resistivity, surface carrier concentration, and mobility on ion dose and on post-implantation anneal temperature was determined. In the case of 60 keV Cd⁺ ions implanted into n-type substrates, a measurable p-type layer resulted when samples were annealed for 10 minutes at a temperature in the range 600—900°C. After annealing at 300—900°C for 10 minutes, 100 per cent electrical activity of the Cd ions resulted for ion doses ≤ 10¹⁴/cm².

The properties of p-type layers produced by implantation of 85 keV Zn⁺ ions were similar to those of the 60 keV cadmium-implanted layers, in that no measurable p-type behavior was observed in samples annealed below a relatively high temperature. However, in samples implanted with 20 keV Zn⁺ ions a p-type layer was observed after annealing for 10 minutes at temperatures as low as 300°C.

Implantation of sulfur ions into p-type GaAs substrates at room temperature resulted in the formation of a high resistivity n-type layer, evcn before any annealing was performed. Annealing at temperatures up to 200°C or above 600°C lowered the resistivity of the layer, while annealing in the range 300—500°C eliminated the n-type layer.