Two-step Pulsed Laser Deposition Research Articles

Effect of thermal annealing on properties of amorphous GaN/p-Si heterojunctions

GaN/Si heterojunctions have been considered as a promising candidate for high-power and high-speed optoelectronic devices. In this paper, the fabrication of amorphous GaN/p-Si heterojunction was carried out by using the two-step pulsed laser deposition (PLD) technology, and its photoelectric properties were further enhanced by thermal annealing in ammonia (NH3) atmosphere. After thermal annealing treatment, blue-shift effect of the optical band gap and space charge effect of the annealed amorphous GaN/p-Si heterojunction were caused by the reduction of N-deficiency, the relatively flat surface and the improved crystalline of GaN films. Besides, a near-red emission band of the EL spectrum was revealed by the annealed amorphous GaN/Si heterojunctions and dominated by interfacial recombination luminescence. This study provides a feasible approach to fabricate GaN/Si-based devices with different emission wavelengths.

Highly active nickel-cobalt/nanocarbon thin films as efficient water splitting electrodes.

Developing low cost, highly active and stable electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) using the same electrolyte has remained a major challenge. Herein, we report a novel and robust material comprised of nickel-cobalt nanoparticles coated on a porous nitrogen-doped carbon (NC) thin film synthesized via a two-step pulsed laser deposition technique. The optimized sample (Ni0.5Co0.5/NC) achieved the lowest overpotentials of 176 mV and 300 mV at a current density of 10 mA cm-2 for HER and OER, respectively. The optimized OER activity might be attributed to the available metal oxide nanoparticles with an effective electronic structure configuration and enhanced mass/charge transport capability. At the same time, the porous nitrogen doped carbon incorporated with cobalt and nickel species can serve as an excellent HER catalyst. As a result, the newly developed electrocatalysts manifest high current densities and strong electrochemical stability in overall water splitting, outperforming most of the previously reported non-precious metal-based catalysts.

Polar and Nonpolar ZnO Nanowire QWs Grown with PLD Using Nanowire Arrays with Tuning Density as Physical Templates

The encountered difficulties that prevent ZnO nanowires from being used as light-emitters are p-type doping and quantum well (QW) integration. The growth of homogenous nanowire quantum wells is usually influenced by the shadowing effect associated with nanowire growth density. In this paper, based on the growth density control of nanowire array, a new two-step pulsed laser deposition (PLD) strategy was demonstrated to grow two kinds of ZnO nanowire QWs, e.g. radial nonpolar QW and axial polar QW. The growth-density control of ZnO nanowires was realised by introducing a wetting layer and adjusting the substrate-target distances. The structural and optical characterizations of these two kinds of nanowire QWs prove that the radial nanowire QWs are more homogenous than axial QWs, which also show better optical properties.

Pulsed laser deposition of ZnO grown on glass substrates for realizing high-performance thin-film transistors

We report characterization of ZnO thin-film transistors (TFTs) on glass substrates fabricated by pulsed laser deposition (PLD). ZnO films were characterized by X-ray diffraction (XRD), atomic force microscopy and Hall effect measurements. The XRD results showed high c-axis-oriented ZnO(0002) diffraction corresponding to the wurtzite phase. Moreover, the crystallization and the electrical properties of ZnO thin films grown at room temperature are controllable by PLD growth conditions such as oxygen gas pressure. The ZnO films are very smooth, with a root-mean-square roughness of 1 nm. From the Hall effect measurements, we have succeeded in fabricating ZnO films on glass substrates with an electron mobility of 21.7 cm2/V s. By using the ZnO thin film grown by two-step PLD and a HfO2 high-k gate insulator, a transconductance of 24.1 mS/mm, a drain current on/off ratio of 4.4×106 and a subthreshold gate swing of 0.26 V/decade were obtained for the ZnO TFT.

Stable p-type ZnO:P nanowire/n-type ZnO:Ga film junctions, reproducibly grown by two-step pulsed laser deposition

ZnO p-n junctions were grown by two-step pulsed laser deposition (PLD) on a-plane sapphire substrates using a Ga-doped ZnO thin film as n-type conducting material. On top of these n-type films, phosphorous-doped ZnO (ZnO:P) nanowires were prepared by high-pressure PLD. Rectifying I-V curves with threshold voltage of about 3.2 V and a forward/reverse current ratio of 100 at ±3.5 V were measured reproducibly on these junctions. There are three independent indications for reproducible and about 1 year stable p-type conductivity of the ZnO:P wires: (1) Low-temperature cathodoluminescence of single ZnO:P nanowires exhibits phosphorus acceptor-related peaks: (A0,X), (e,A0), and donor-acceptor pair [B. Q. Cao et al., Nanotechnology 18, 455707 (2007)], (2) bottom-gate field effect transistors using undoped (n-type) ZnO and ZnO:P wires showed opposite transfer characteristics [B. Q. Cao et al., Phys. Status Solidi (RRL) 2, 37 (2008)], and (3) the rectifying I-V characteristics of the ZnO:P nanowire/ZnO:Ga-film junctions as shown here.

Characteristics of plasma hydrogenated ZnO films oriented along the (11–20) plane grown by pulsed laser deposition

Single crystalline phase ZnO layers oriented along the (11–20) plane were successfully grown on (1–102) sapphire substrate by using a modified two-step pulsed laser deposition process. The full width at half maximum of rocking curve for (11–20) ZnO was 430 arc sec. After a hydrogen plasma treatment, the value of surface roughness was decreased from 37.5 to 10.2 nm. And the intensity of ultra-violet emission at 380 nm in cathodoluminescence (CL) spectrum was greatly increased by the hydrogen plasma irradiation. In the time-resolved photoluminescence (TRPL) spectra, the minimum value of decay time was 36 ps after the hydrogen plasma irradiation for 5 min. Especially, CL and TRPL results show the potential of high efficient optoelectronic devices by using the hydrogen plasma treatment.

Morphology evolution and local electric properties of Au nanoparticles on ZnO thin films

We report the sequential two-step pulsed laser deposition of nanostructures consisting of ZnO thin films covered with Au nanoparticles. Zn and Au targets were alternatively submitted to pulses generated by a frequency tripled Nd:yttrium aluminium garnet (λ=355nm, τ∼10ns, ν=10Hz) laser. The ZnO films were synthesized in 20Pa oxygen pressure, whereas the subsequent Au coverage was applied in vacuum. The dynamics of Au nanoparticles grown on the ZnO thin-films surface was studied by atomic force microscopy as a function of number of laser pulses applied for the ablation of the Au target. The nanoparticle diameters increase with the number of laser pulses while their height decreases. The local electric properties of the uncoated (reference) and coated with Au ZnO thin films was investigated by current sensing mode atomic force microscopy.

Ferroelectric Properties of (PbxLa1-x)(ZryTi1-y)O3 Thin Films Prepared by Modified Pulsed Laser Deposition Process

A two-step pulsed laser deposition (PLD) process, including PLD at a substrate temperature lower than 150°C and rapid thermal annealing (RTA) at around 550°C (30 s), has been successfully applied for growing (PbxLa1-x)(ZryTi1-y)O3, (PLZT, x=0.97, y=0.664) thin films. Fatigue-free, large remanent polarization, Pr=19 µC/cm2, (with coercive field Ec=78 kV/cm and low leakage current density Jl ≤1 ×10-5 A/cm2 at 400 kV/cm) characteristics can be achieved when a SrRuO3 layer is used as a buffer layer. Interdiffusion between layers remains pronounced when an amorphous SrRuO3 layer is used as a buffer layer, which markedly degrades the electrical properties of PLZT films. Only the crystalline SrRuO3 layer can effectively suppress the interdiffusion of species and improve the ferroelectric behavior of the PLZT films. Such a modified PLD process possesses an overwhelming advantage over the in situ PLD process in terms of its simplicity and compatibility with device fabrication processes.

Ferroelectric properties of (PbxLa1−x)(ZryTi1−y)O3 films prepared by two-step pulsed laser deposition process

A two-step pulsed laser deposition process has been successfully applied for growing the (PbxLa1−x)(ZryTi1−y) O3, PLZT, thin films. These films exhibit good ferroelectric characteristics (Pr=18 μC/cm2; E c=80 kV/cm; J L≤0.2 μA/cm2), whenever crystalline SrRuO3 materials were used as buffer layers. However, the electrical properties of PLZT films were markedly degraded whenever the amorphous SrRuO3 or (La0.5Sr0.5)CoO3 layer was used as buffer layer.

Effect of Characteristics of SrRuO3 Buffer Layer on the Ferroelectric Properties of (Pb0.97La0.30)(Zr0.66Ti0.34)O3 Thin Films

AbstractA two-step pulsed laser deposition (PLD) process, including PLD at a substrate temperature lower than 150°C and rapid-thermal-annealing (RTA) at around 550°C (30 s), has been successfully applied for growing (Pb0.97La0.03)(Zr0.66Ti0.034)0.9875O3, PLZT, thin films. Interdiffusion between layers is pronouncedly suppressed due to the presence of the SrRuO3 layer, which markedly improves the electrical properties of PLZT films. The PLZT films thus obtained exhibit large remanent polarization P,=19 µC/cm2 (with coercive force Ec=78 kV/cm), low leakage current density J11≤8 × 1O−6 A/cm2 (up to 400 kV/cm) and fatigue free characteristics.