Ferromagnetic and transport properties of highly Mn-doped ZnSnAs2 epitaxial layers on InP substrates

Ternary ZnSnAs₂ thin films heavily doped with nominal 10 and 20% Mn content on InP (001) substrates are grown using low-temperature molecular beam epitaxy and their magnetic and transport properties are investigated for the first time. It is found that the Mn-doped ZnSnAs₂ thin films are pseudomorphically grown on nearly lattice-matched InP (001) substrates, and a trace amount of secondary phase MnAs formation is observed by high-resolution X-ray diffraction (HR-XRD) measurements. Magnetization measurements on Mn-doped ZnSnAs₂ thin films reveal that the Curie temperature is around 334 K. Nominal magnetic moments per Mn atom measured from the saturation magnetization of hysteresis loops at 5 K have been estimated as 5.28 and 4.17 μ_B for 10% and 20% Mn-doped ZnSnAs₂ thin films, respectively. We have found from Hall effect measurements that the 10% and 20% Mn-doped ZnSnAs₂ films exhibit n-type conduction, in contrast to p-type conduction in ZnSnAs₂ doped with less than 10% Mn. This is likely related to the presence of a certain amount of Mn interstitials or Mn³⁺ substitution on Zn site in the samples.     

Raman scattering and Rutherford backscattering studies on InN films grown by plasma-assisted molecular beam epitaxy

A series of InN thin films was grown on sapphire substrates via plasma-assisted molecular beam epitaxy (PA-MBE) with different nitrogen plasma power. Various characterization techniques, including Hall, photoluminescence, Raman scattering and Rutherford backscattering, have been employed to study these InN films. Good crystalline wurtzite structures have been identified for all PA-MBE grown InN films on sapphire substrate, which have narrower XRD wurtzite (0002) peaks, showed c-axis Raman scattering allowed longitudinal optical (LO) modes of A₁ and E₁ plus E₂ symmetry, and very weak backscattering forbidden transverse optical (TO) modes. The lower plasma power can lead to the lower carrier concentration, to have the InN film close to intrinsic material with the PL emission below 0.70 eV. With increasing the plasma power, high carrier concentration beyond 1 × 10²⁰ cm^− 3 can be obtained, keeping good crystalline perfection. Rutherford backscattering confirmed most of InN films keeping stoichiometrical In/N ratios and only with higher plasma power of 400 W leaded to obvious surface effect and interdiffusion between the substrate and InN film.     

Growing InN films by plasma-assisted metalorganic vapor-phase epitaxy on Al2O3 and YSZ substrates in plasma generated by gyrotron radiation under electron cyclotron resonance conditions

Hexagonal indium nitride (InN) films on (111)- and (100)-oriented yttria-stabilized zirconia (YSZ) substrates and (0001)-oriented Al₂O₃ substrates have been grown for the first time at a rate of 1 μm/h by the method of metalorganic vapor-phase epitaxy with plasma-assisted nitrogen activation in an electron cyclotron resonance discharge generated by gyrotron radiation at low-temperature (350°C) growth. InN films grown without buffer layers possess a textured polycrystalline structure. Using an InN/GaN double buffer layer, single-crystalline InN films have been obtained on Al₂O₃(0001) substrates. Data on the morphology, structure, and photoluminescent properties of the obtained InN films are presented.     

Optical properties of plasma-assisted molecular beam epitaxy grown InN/sapphire

The optical properties of as-grown InN/sapphire films prepared by plasma assisted molecular beam epitaxy (PA-MBE) are characterized by photoluminescence (PL), Raman scattering (RS) and infrared (IR) reflectance techniques. The PL measurements have consistently exhibited lower values of InN band gaps providing clear indications of electron concentration dependent peak energy shifts and widths. The phonon modes identified by RS are found to be in good agreement with the grazing inelastic X-ray scattering measurements and ab initio lattice dynamical calculations. An effective medium theory used to analyze IR reflectance spectra of InN/sapphire films has provided reasonable estimates of free charge carrier concentrations.     

Growth of A3N whiskers and plate-shaped crystals by molecular-beam epitaxy with the participation of the liquid phase

It is shown that InN and GaN whiskers and plate-shaped crystals can be grown by molecular-beam epitaxy (MBE), and the growth mechanism on gallium arsenide and sapphire substrates is investigated. A comparison is made with the theory. It is proved that the growth mechanism corresponds to the vapor-liquid-solid (VLS) mechanism, and the parameters of the crystallization process are determined. The nanometer sizes of the crystals grown give hope that the crystals and the VLS growth method itself can be used to obtain quantum-size objects (quantum dots and wires) by MBE in the promising system of elements A³B⁵-AlGaInN. Pis’ma Zh. Tekh. Fiz. 25, 55–63 (September 26, 1999)     

Epitaxial growth of InN on c-plane sapphire by pulsed laser deposition with r.f. nitrogen radical source

We have grown InN films on c-plane sapphire substrates by pulsed laser deposition (PLD) with a radio frequency nitrogen radical source for the first time and investigated the effect of the substrate surface nitridation on the structural and electrical properties of InN films with reflection high energy electron diffraction (RHEED), atomic force microscope, the Hall effect measurements and high-resolution X-ray diffraction (HRXRD). RHEED and HRXRD characterizations revealed that high-quality InN grows epitaxially on sapphire by PLD and its epitaxial relationship is InN (0 0 0 1)∣∣sapphire (0 0 0 1) and InN [2 -1 -1 0]∣∣sapphire [1 0 -1 0]. The InN crystalline quality and the electron mobility are improved by the substrate nitridation process. The area of the pits at the InN surface is reduced by the substrate nitridation process probably due to the reduction in the interface energy between InN and the substrate. The full width at half maximum of the -1 -1 2 4 X-ray rocking curve for InN grown by the present technique without using any buffer layers was as small as 34.8 arcmin. These results indicate that the present technique is promising for the growth of the high-quality InN films.     

Structure and optical properties of InN and InAlN films grown by rf magnetron sputtering

The structure and optical properties of InN and In-rich InAlN films grown by magnetron sputtering were investigated. The XRD results show that these films are highly c-axis oriented. The film morphology and microstructure of these films were observed by AFM and SEM which reveals that the films grown in island growth mode. Optical properties of these films were studied by absorption method. The band gap energy of the InN film grown under substrate temperature of 400 °C is 1.38 eV. By studying the E _g values of InN films deposited under different substrate temperature, the Burstein-Moss effect on band gap of InN was examined. The significant band gap bowing of our In-rich InAlN films was found to be correlated with the In contents. The bowing parameter of 3.68 eV was obtained which is in agreement with previous theoretical predictions.     

Oxidation study of polycrystalline InN film using in situ X-ray scattering and X-ray photoemission spectroscopy

Oxidation process of polycrystalline InN films were investigated using in situ X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS). The films were grown by dc sputter on sapphire (0001) substrates and were oxidized in air at elevated temperatures. The XRD data showed that the structure of the films changed to the bixbyite In₂O₃ (a = 10.11 Å) above 450 °C. Chemical configurations of the sample surfaces were investigated using high-resolution XPS. For the non-intentionally oxidized InN film, XPS analysis on the In 3d peak and the N 1s main peak at 396.4 eV suggests that indium and nitrogen are bound dominantly in the form of InN. An additional peak observed at 397.4 eV in the N 1s photoelectrons and the O 1s peaks indicate that the InN film surface is partly oxidized to have InO_xN_y configuration. After oxidation of the InN film at elevated temperature, the O 1s spectrum is dominated by In₂O₃ peak, which indicates that the structure is stable chemically with In₂O₃ configuration at least within the XPS probing depth of a few nm.     

A comparative study of InN growth on quartz,silicon, C-sapphire and bulk GaN substrates by RF magnetron sputtering

In this work, we investigate the growth of indium nitride (InN) films on quartz, bulk GaN, sapphire (001) and Si (111) substrates. An InN buffer layer was first deposited on all the substrates, then an InN film was grown on bare substrate and InN buffered substrates. The films were polycrystalline in nature with preferred orientation along (002) plane. Best structural quality was observed on InN buffered Si substrate. The structural properties were explained by calculating the full width at half maximum, crystallite size, micro-strain, and dislocation density. The morphology of the films revealed similar granular features except for bare sapphire substrate which showed cracks and more oxygen percentage. The application of buffer layer increased the surface roughness for quartz and reduced in other cases. The band gap of InN films was determined using UV–visible reflectance spectroscopy. The lowest band gap value was observed for InN buffered quartz substrate.     

Growth of InN layers on Si (111) using ultra thin silicon nitride buffer layer by NPA-MBE

Indium nitride (InN) epilayers have been successfully grown by nitrogen-plasma-assisted molecular beam epitaxy (NPA-MBE) on Si (111) substrates using different buffer layers. Growth of a (0001)-oriented single crystalline wurtzite-InN layer was confirmed by high resolution X-ray diffraction (HRXRD). The Raman studies show the high crystalline quality and the wurtzite lattice structure of InN films on the Si substrate using different buffer layers and the InN/β-Si₃N₄ double buffer layer achieves minimum FWHM of E₂ (high) mode. The energy gap of InN films was determined by optical absorption measurement and found to be in the range of ~ 0.73-0.78 eV with a direct band nature. It is found that a double-buffer technique (InN/β-Si₃N₄) insures improved crystallinity, smooth surface and good optical properties.     

Growth and characterization of Fe3O4 films

Iron oxide films were grown on sapphire substrates by pulsed laser deposition at substrate temperatures between 100 and 700 °C. X-ray diffraction, Raman spectroscopy, and vibrational sample magnetometer analysis revealed that structural and magnetic properties of the iron oxide films strongly depend on the substrate temperature during growth. Single phase Fe₃O₄ film was successfully grown on sapphire substrate at a substrate temperature of 500 °C. The saturation magnetic moment of the single phase Fe₃O₄ film is 499 emu/cm³, which is in good agreement with the value reported for bulk magnetite, suggesting the Fe₃O₄ film is of high crystal quality without antiphase boundaries.     

Annealing effect on dielectric and leakage current characteristics of Mn-doped Ba0.6Sr0.4TiO3 thin films as gate insulators for low voltage ZnO thin film transistor

We report on the dielectric properties and leakage current characteristics of 3 mol% Mn-doped Ba_0.6Sr_0.4TiO₃ (BST) thin films post-annealed up to 600 °C following room temperature deposition. The suitability of 3 mol% Mn-doped BST films as gate insulators for low voltage ZnO thin film transistors (TFTs) is investigated. The dielectric constant of 3 mol% Mn-doped BST films increased from 24 at in-situ deposition up to 260 at an annealing temperature of 600 °C due to increased crystallinity and the formation of perovskite phase. The measured leakage current density of 3 mol% Mn-doped BST films remained on the order of 5 × 10^− 9 to 10^− 8 A/cm² without further reduction as the annealing temperature increased, thereby demonstrating significant improvement in the leakage current characteristics of in-situ grown Mn-doped BST films as compared to that (5 × 10^− 4 A/cm² at 5 V) of pure BST films. All room temperature processed ZnO-TFTs using a 3 mol% Mn-doped BST gate insulator exhibited a field effect mobility of 1.0 cm²/Vs and low voltage device performance of less than 7 V.     

Stress reduction and electric properties of InSb thin films grown by metalorganic vapor phase epitaxy on sapphire substrates with an InAs buffer layer

InSb thin films were grown by metalorganic vapor phase epitaxy using an InAs buffer layer on sapphire (0001) substrates. The stresses and strains in InSb were controlled by the thickness of the InAs buffer layer, and it was found that with decreasing compressive stress in InSb, the crystalline quality and the electrical properties improved. The thermoelectric properties of InSb were assessed and it was found that the power factor of InSb with a thickness of 5 μm reached as high as 5.8 × 10⁻³ W/mK² at 600 K.     

Near-infrared photoluminescence of vertically aligned InN nanorods grown on Si(111) by plasma-assisted molecular-beam epitaxy

We demonstrate that vertically aligned InN nanorods have been grown on Si(111) substrates by plasma-assisted molecular-beam epitaxy (PA-MBE) at low and high growth temperatures (LT- and HT-InN nanorods). High-resolution scanning electron microscopy images clearly show that InN nanorods grown on Si(111) are hexagonal in shape, vertically aligned, well separated and densely distributed on the substrate. The size distribution of LT-InN nanorods is quite uniform, while the HT-InN nanorods exhibit a broad, bimodal distribution. The structural analysis performed by Raman scattering indicates that PA-MBE grown InN nanorods have the wurtzite-type InN single-crystal structure with the rod axis (growth direction) along the c-axis. In addition, both types of nanorods contain high concentrations of electrons (unintentionally doped). Compared to the HT-InN nanorods and the PA-MBE-grown InN epitaxial film, the LT-grown InN nanorods have a considerable number of structural defects. Near-infrared photoluminescence (PL) from LT- (∼ 0.77 eV) and HT-InN (∼ 0.70 eV) nanorods is clearly observed at room temperature. In comparison with the LT-InN nanorods, the PL efficiency of HT-InN nanorods is better and the PL peak energy is closer to that of InN-on-Si epitaxial films (∼ 0.66 eV). We also find that the PL band at low temperatures from nanorods is significantly weaker (compared to the InN film case) and exhibits anomalous temperature effects. We propose that these PL properties are results of considerable structural disorder (especially for the LT-InN nanorods) and strong surface electron accumulation effect (for both types of nanorods).     

Preparation of large area free-standing GaN substrates by HVPE using mechanical polishing liftoff method

In this study, 30×30 mm² free-standing GaN substrates were fabricated from 400–450 μm thick GaN films grown on (0001) sapphire by hydride vapor phase epitaxy (HVPE). The thick films were separated from the substrate by mechanical polishing liftoff method, using a diamond slurry. After liftoff, the bow is only slight or absent in the resulting free-standing GaN wafers.     

Properties of LiNbO3 based heterostructures grown by pulsed-laser deposition for optical waveguiding application

Epitaxial LiNbO₃ (LN) thin films have been grown onto (00.1) Al₂O₃ substrates and onto sapphire covered with a conductive ZnO buffer layer. For the two systems, the LN thin films are well crystallised and highly (00.1) oriented. Epitaxial relationships between the different layers are evidenced both on the LN/sapphire film and the LN/ZnO/sapphire heterostructure. The optical waveguiding propagation losses of the LN/sapphire films are very low (1 ± 0.5 dB/cm) while the LN/ZnO/sapphire heterostructure does not exhibit satisfying waveguiding properties mainly due to the high conductivity (600 S m^− 1) of the ZnO buffer layer.     

Properties of Heavily Mn-doped GaMnAs with Curie Temperature of 172.5 K

The authors have investigated the magnetic properties of heavily Mn-doped ferromagnetic semiconductor Ga_1−x Mn _x As thin film with the Mn concentration x of 15.2% grown by molecular-beam epitaxy at relatively high growth temperature of 250 °C. Magnetic circular dichroism and the anomalous Hall effect measurements indicate that this thin film holds the intrinsic ferromagnetic semiconductor features. By low-temperature annealing, the resistivity was significantly decreased and the Curie temperature was largely enhanced from 95 K to 172.5 K.     

Investigation on Mn doped ZnO thin films grown by RF magnetron sputtering

In this paper, we have investigated the Zn_1 − x Mn_xO (x = 0.05, 0.10 and 0.15) thin films grown by RF magnetron sputtering. The grown films on sapphire [Al₂O₃(0001)] substrates have been characterized using X-ray Diffraction (XRD), Photoluminescence (PL) and Vibrating Sample Magnetometer (VSM) in order to investigate the structural, optical and magnetic properties of the films respectively. It is observed from XRD that all the films are single crystalline with (002) preferential orientation along c-axis. PL spectra reveal that the addition of Mn marginally shifts the Near Band Edge (NBE) position towards the higher energy side. The magnetic measurements of the films using VSM clearly indicate the ferromagnetic nature.     

Growth of p-type ZnO thin films by using an atomic layer epitaxy technique and NH3 as a doping source

Nitrogen-doped, p-type ZnO thin films have been grown successfully on sapphire (0001) substrates by atomic layer epitaxy (ALE) using Zn(C₂H₅)₂ [Diethylzinc, DEZn], H₂O and NH₃ as a zinc precursor, an oxidant and a doping source gas, respectively. The lowest electrical resistivity of the p-type ZnO films grown by ALE was 210 Ω cm with a hole concentration of 3.41 × 10¹⁶ cm^− 3. Low temperature-photoluminescence analysis results support that the nitrogen ZnO after annealing is a p-type semiconductor. Also a model for change from n-type ZnO to p-type ZnO by annealing is proposed.     

Growth and characterization of laser-deposited Ag-doped YBa2Cu3O7−x thin films on bare sapphire

Microstructural and superconducting properties of YBa₂Cu₃O_7−x thin films grownin situ on bare sapphire by pulsed laser deposition using YBa₂Cu₃O_7−x targets doped with 7 and 10 wt% Ag have been studied. Ag-doped films grown at 730°C on sapphire have shown very significant improvement over the undoped YBa₂Cu₃O_7−x films grown under identical condition. A zero resistance temperature of 90 K and a critical current density of 1·2×10⁶ A/cm² at 77 K have been achieved on bare sapphire for the first time. Improved connectivity among grains and reduced reaction rate between the substrate and the film caused due to Ag in the film are suggested to be responsible for this greatly improved transport properties.