As-doped ZnO Films Research Articles

Fabrication of p-Type ZnO Films Grown on Arsenic-Implanted Silicon via Thermal Diffusion at Various Substrate Temperatures

P-type ZnO films fabricated using the diffusion method with arsenic (As)-implanted silicon substrates as the source of dopants are investigated. The diffusion method is not restricted by the substrate and various dopants can be used in the implantation process. We demonstrate that stable p-type conduction appears at a proper substrate temperature (TS). The best crystallinity and electrical properties of the p-type ZnO films were obtained at TS = 400°C. The maximum carrier concentration of the As dopant was 6.7 × 1018 cm−3 and the resistivity reached 1.1×10−1 Ω-cm. The reproducible As-doped ZnO films can be obtained by this diffusion method.

Structural, electronic, and optical properties of nanocrystalline As-doped ZnO films on quartz substrates determined by Raman scattering and infrared to ultraviolet spectra

Nanocrystalline As-doped ZnO films with different laser power energy (40 mJ and 55 mJ) and As doping concentrations (C As from 1% to 3%) have been grown on quartz substrates by pulsed laser deposition. The average grain size of the films was calculated from the (002) peak of x-ray diffraction patterns and is estimated to vary from 9 to 13 nm. Electronic transitions and optical properties of the films have been investigated by Raman scattering, far-infrared reflectance, and infrared-ultraviolet spectral transmittance technique. With increasing doping concentration, the A 1 longitudinal optical phonon mode shifts towards the lower energy side and can be described by (564-75C As) cm -1 owing to the increment of free carrier concentration. The E 1 transverse optical phonon frequency is located at about 415 cm -1 and does not show an obvious decreasing trend with the C As. The optical constants in the photon energy range of 0.5–6.5 eV have been extracted by fitting the experimental data with the Adachi's model. The refractive index dispersion in the transparent region can be well expressed by a Sellmeier's single oscillator function. Due to different doping concentration and hexagonal crystalline structure, the optical band gap of the films grown at 40 mJ linearly decreases with increasing As concentration. The phenomena agree well with the results from the theoretical calculations.

Van der Pauw Hall Measurement on Intended Doped ZnO Films for p-Type Conductivity

A Van der Pauw Hall measurement is performed on the intended doped ZnO films (Na doped ZnO) grown by using the molecular beam epitaxial method. All as-grown samples show n-type conductivity, whereas the annealed samples (annealing temperature 900° C) show ambiguous carrier conductivity type (n- and p-type) in the automatic Van der Pauw Hall measurement. A similar result has been observed in Li doped ZnO and in as-doped ZnO films by other groups before. However, by tracing the Hall voltage in the Van der Pauw Hall measurement, it is found that this alternative appearance of both n- and p-type conductivity is not intrinsic behavior of the intended doped ZnO films, but is due to the persistent photoconductivity effect in ZnO. The persistent photoconductivity effect would strongly affect the accurate determination of the carrier conductivity type of a highly resistive intended doped ZnO sample.

Effect of Arsenic Implantation Dose on p-Type ZnO Films Obtained via Thermal Diffusion from Silicon Substrates

Arsenic (As)-doped ZnO films were obtained via thermal diffusion from low energy high dose implanted silicon substrates using thermal treatment. The implantation conditions, such as implantation dose and energy, were adjusted to allow more nonactivated dopants in the surface region of the substrate and to outdiffuse into ZnO films efficiently. With the proper implantation dose and energy, the ZnO films exhibited p-type conduction, which increased the hole concentration and preservation time in the air ambient. The maximum carrier concentration of the As-doped ZnO films was 8.06 X 10 18 cm -3 , and the resistivity reached 1.63 × 10 -1 Ω cm.

Arsenic doped p-type zinc oxide films grown by radio frequency magnetron sputtering

As-doped ZnO films were grown by the radio frequency magnetron sputtering method. As the substrate temperature during growth was raised above ∼400 °C, the films changed from n type to p type. Hole concentration and mobility of ∼6×1017 cm−3 and ∼6 cm2 V−1 s−1 were achieved. The ZnO films were studied by secondary ion mass spectroscopy, x-ray photoelectron spectroscopy (XPS), low temperature photoluminescence (PL), and positron annihilation spectroscopy (PAS). The results were consistent with the AsZn–2VZn shallow acceptor model proposed by Limpijumnong et al. [Phys. Rev. Lett. 92, 155504 (2004)]. The results of the XPS, PL, PAS, and thermal studies lead us to suggest a comprehensive picture of the As-related shallow acceptor formation.

Studies of the mechanism of electrical conduction in As-doped ZnO by structural and chemical-bonding analyses and first principle calculations

X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and first-principle density-functional theory (DFT) calculations are carried out on the p -type As-doped ZnO (ZnO:As) films prepared by pulsed laser deposition (PLD). XRD results indicate that defects are induced by As incorporation in ZnO lattice structure. The XPS analyses demonstrate that As atoms locate Zn-sites in ZnO:As films. Based on XRD and XPS results, it can be suggested that some forms of As Zn (As occupies Zn site) related complexes construct acceptors. First-principle density-functional calculations can show the electronic structures of several possible As Zn-related complexes in ZnO:As. The calculation results show that an As Zn–2V Zn (an As atom occupies a Zn site and induces two nearby Zn vacancies) complex can be a shallow acceptor in ZnO.

As-doped p-type ZnO films grown on SiO 2/Si by radio frequency magnetron sputtering

p-Type ZnO:As films with a hole concentration of 10 16–10 17 cm −3 and a mobility of 1.32–6.08 cm 2/V s have been deposited on SiO 2/Si substrates by magnetron sputtering. XRD, SEM, Hall measurements are used to investigate the structural and electrical properties of the films. A p–n homojunction comprising an undoped ZnO layer and a ZnO:As layer exhibits a typical rectifying behavior. Our study demonstrates a simple method to fabricate reproducible p-type ZnO film on the SiO 2/Si substrate for the development of ZnO-based optoelectronic devices on Si-based substrates.

Effects of substrate temperature on structural, electrical and optical properties of As-doped ZnO films

As-doped ZnO films were prepared by co-sputtering ZnO and Zn 3As 2 targets on glass substrates at various temperatures from 250 to 500 °C. The effects of substrate temperature on structural, electrical and optical properties of the films were investigated. The films grown at temperatures from 250 to 400 °C were c-axis oriented and those deposited above 400 °C exhibited poor crystallinity. Hall measurement showed that p-type ZnO:As films were prepared at different temperatures. With increasing the substrate temperature from 250 to 500 °C, the optical band gap ( E g) first decreased, and then increased. The E g changes upon the substrate temperature were due to the effect of substrate temperature on the crystallinity of ZnO films.

Visual-infrared electroluminescence emission from ZnO∕GaAs heterojunctions grown by metal-organic chemical vapor deposition

The light-emitting diode of p-ZnO∕n-GaAs heterojunction was grown by metal-organic chemical vapor deposition. The p-ZnO films have been formed by the doping As atoms which diffuse into ZnO film from GaAs substrate. The p-type behavior of As-doped ZnO films based on As-doped p-ZnO∕n-GaAs, p-ZnO∕p-GaAs heterojunction was studied by carrying out I-V measurements and x-ray photoelectron spectroscopy. The I-V characteristic of p-ZnO∕n-GaAs heterojunction showed characteristic of rectifying diode and visual-infrared electroluminescence emission under forward current injection at room temperature. The I-V of the heterounction had a threshold voltage of ∼2.5V.

As-doped p-type ZnO films prepared by cosputtering ZnO and Zn 3As 2 targets

p-Type ZnO:As films with hole concentration of 10 16–10 17 cm −3 were deposited on glass substrates by cosputtering method with ZnO and Zn 3As 2 targets. Proper annealing may change the conduction type of ZnO:As film. Ohmic contacts were established between Ti electrodes and ZnO films. X-ray photoelectron spectroscopy (XPS) showed that the bonding state of As in ZnO:As film was in its oxidization state. The optical band gap of the ZnO films blueshifted from 3.22 to 3.34 eV in our experiment. Our results not only demonstrated a new approach to obtain p-type ZnO films but also helped to understand the microscopic structure of As in As-doped ZnO.

As-doped p-type ZnO films by sputtering and thermal diffusion process

As-doped p-type ZnO films were grown on GaAs by sputtering and thermal diffusion process. Hall effect measurements showed that the as-grown films were of n-type conductivity and they were converted to p-type behavior after thermal annealing. Moreover, the hole concentration of As-doped p-type ZnO was very impressible to the oxygen ambient applied during the annealing process. In addition, the bonding state of As in the films was investigated by x-ray photoelectron spectroscopy. This study not only demonstrated an effective method for reliable and reproducible p-type ZnO fabrication but also helped to understand the doping mechanism of As-doped ZnO.

Doping of As, P and N in laser deposited ZnO films

Preparation of p-type ZnO thin films on Al 2O 3 (0 0 0 1) substrates is reported, which involves two different p-type dopant source materials such as Zn 3As 2 and Zn 3P 2 for As and P doping, respectively, during pulsed laser deposition, while an ion implantation method was used to dope N in the ZnO films. The hole concentrations of 2.5×10 17–1.2×10 18 cm −3 have been observed in As-doped p-type ZnO films after being underwent rapid thermal annealing (RTA) at 200 °C under an N 2 ambient. In the case of P doping, 3 mol% P-doped ZnO films at RTA between 600 and 800 °C under an O 2 ambient exhibited p-type behavior with the hole concentrations of 5.1×10 14–1.5×10 17 cm −3. In the case of N doping, after RTA up to 700 °C, films implanted with an N dose of 1×10 12 ions/cm 2 showed p-type conductivity with a hole concentration of ∼6.01×10 17 cm −3 and a low resistivity of ∼5.2×10 −1 Ω cm. The low-temperature photoluminescence results showed the peak associated with the neutral-acceptor bound exciton ( A°, X) emission only in the films showing p-type behavior.

Preparation of As-doped p-type ZnO films using a Zn3As2∕ZnO target with pulsed laser deposition

We report the preparation of arsenic doped p-type ZnO films using a Zn3As2∕ZnO target by pulsed laser deposition. Zn3As2 was used as a p-type dopant source material for arsenic doping in ZnO. The existence of As in the As-doped ZnO films was confirmed by the x-ray photoelectron spectroscopy study. The p-type behavior of the As-doped ZnO films was determined by the Hall and photoluminescence measurements. Room temperature Hall measurements revealed that the As-doped ZnO films exhibited p-type conductivity after being annealed at 200°C in N2 ambient for 2min with the hole concentrations varied between 2.48×1017 and 1.18×1018cm−3. The resistivity and carrier mobility of the As-doped p-type ZnO films were in the range of 2.2–6.7Ωcm and 0.83–11.4cm2∕Vs, respectively. The low temperature photoluminescence measurements confirmed the peak associated with the neutral-acceptor bound exciton (A0X) emission in the As-doped p-type ZnO films.

The fabrication and characterization of ZnO UV detector

ZnO films were deposited on GaAs substrates by radio frequency (rf) magnetron sputtering followed by an ambient-controlled heat treatment process for arsenic doping. In Hall measurements, the As-doped ZnO films showed the characteristics of p-type semiconductor. The ZnO thin film p–n homojuctions were then fabricated to investigate the electrical properties of the films. The p–n homojunctions exhibited the distinct rectifying current–voltage ( I– V) characteristics. The turn-on voltage was measured to be ~3.0 V under the forward bias. When ultraviolet (UV) light (λ = 325 nm) was irradiated on the p–n homojunction, photocurrent of ~2 mA was detected. Based on these results, it is proposed that the p–n homojunction herein is a potential candidate for UV photodetector and optical devices.

Fabrication and properties of As-doped ZnO films grown on GaAs(0 0 1) substrates by radio frequency (rf) magnetron sputtering

ZnO thin films were grown on GaAs(0 0 1) substrate to study the feasibility of making As-doped textured ZnO films for possible optical device application using radio frequency (rf) magnetron sputtering. It was demonstrated that highly c-axis oriented ZnO crystal with uniformly doped As could be grown using this deposition technique. Crystallinity was shown to improve with higher processing temperature. Photoluminescence spectroscopy, supplemented by cathodo-luminescence imaging, showed that the ZnO films have good optical quality with strong near band emission peak at 3.3 eV and spatially homogeneous luminescence indicating possibility of producing As-doped ZnO films with good crystallinity and optical properties using the technique used herein.

Properties of arsenic-doped p-type ZnO grown by hybrid beam deposition

As-doped ZnO (ZnO:As) films have been characterized. ZnO:As films show p-type characteristics determined by Hall-effect and photoluminescence (PL) measurements. The hole concentration can be increased up to the mid-1017-cm−3 range. The thermal binding energy of the As acceptor (EAth-b) is 120±10 meV, as derived from temperature-dependent Hall-effect measurements. The PL spectra reveal two different acceptor levels (EAopt-b), located at 115 and 164 meV, respectively, above the maximum of the ZnO valence band, and also show the binding energy of the exciton to the As-acceptor (EAXb) is about 12 meV. The values of the ratio EAXb/(EAth-b or EAopt-b) are located in the range from 0.07 to 0.11.