High Hall Mobility Research Articles

Hall mobility in tin iodide perovskite CH3NH3SnI3: Evidence for a doped semiconductor

Abstract CH3NH3SnI3 is a metal halide perovskite that shows metallic conductivity over a wide temperature range, although ab initio calculations and optical absorption indicate that its band structure is consistent with that of an intrinsic semiconductor. Hall effect measurements of as-grown crystals give a hole concentration of about 9×1017 cm−3 with rather high Hall mobility of about 200 cm2 V−1 s−1 at 250 K. Artificial hole doping enhances the electrical conductivity of the crystals without influencing mobility. These observations indicate that the electronic structure in stoichiometric CH3NH3SnI3 can be described as that of an intrinsic semiconductor with a wide valence band. This situation leads to metal-like conduction with even a trace amount of spontaneous hole doping in the as-grown crystal.

Effects of Doping Ratio and Thermal Annealing on Structural and Electrical Properties of Boron-Doped ZnO Thin Films by Spray Pyrolysis

Boron-doped zinc oxide (BZO) thin films have been fabricated by spray pyrolysis on a glass substrate. The morphology and electrical properties of the thin films were investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were performed. It was found that [B]/[Zn] ratio altered both the microstructure and concentration of the BZO thin films. The film grain size was reduced by increasing the [B]/[Zn] ratio. The highest Hall mobility was 3.65 cm2 V-1 s-1 for the undoped ZnO thin film, and the highest carrier concentration of 1.0×1019 cm-3 was achieved for the as-deposited BZO thin film with [B]/[Zn] = 1.5 at. %. Conductivity was determined at different measurement temperatures and shallow donors provided the dominate conduction mechanism for the as-deposited BZO thin films. After 600 °C annealing, shallow level reduction and donors with a high activation energy of 129±6 meV in the BZO thin films were characterized, and the shallow donors that dominate the carrier concentration for the as-deposited spray-pyrolized BZO thin film were eliminated.

Properties of low-temperature deposited ZnO thin films prepared by cathodic vacuum arc technology on different flexible substrates

Un-doped zinc oxide (ZnO) films were deposited on three different substrates (polyethylene terephthalate (PET), polyvinyl butyral (PVB) and polyimide (PI)) at a low temperature (<75°C) by cathode vacuum arc deposition. The microstructure, optical and electrical properties of the deposited films were investigated and discussed. All the deposited films reveal a preferred orientation with the c-axis perpendicular to the substrate, and an average transmittance of over 85% in the visible region. The calculated optical band gaps are around 2.6, 3.14 and 3.18eV, respectively, for the ZnO films deposited on the PI, PVB and PET substrates. The lowest resistivity and the highest Hall mobility are 5.31×10−3Ω-cm and 15.16cm2/V-s for the ZnO film deposited on the PET substrate.

Effect of thickness on optoelectrical properties of Nb-doped indium tin oxide thin films deposited by RF magnetron sputtering

Niobium-doped indium tin oxide (ITO:Nb) thin films are prepared on glass substrates with various film thicknesses by radio frequency (RF) magnetron sputtering from one piece of ceramic target material. The effects of thickness (60–360 nm) on the structural, electrical and optical properties of ITO: Nb films are investigated by means of X-ray diffraction (XRD), ultraviolet (UV)-visible spectroscopy, and electrical measurements. XRD patterns show the highly oriented (400) direction. The lowest resistivity of the films without any heat treatment is 3.1×10−4Ω·cm−1, and the resistivity decreases with the increase of substrate temperature. The highest Hall mobility and carrier concentration are 17.6 N·S and 1.36×1021 cm−3, respectively. Band gap energy of the films depends on substrate temperature, which varies from 3.48 eV to 3.62 eV.

Temperature-dependent growth and properties of W-doped ZnO thin films deposited by reactive magnetron sputtering

Tungsten doped zinc oxide (WZO) thin films have been deposited by pulsed direct-current (DC) reactive magnetron sputtering technique. The microstructure, surface morphology, optical and electrical properties of WZO thin films were investigated at different substrate temperatures. Experimental results indicate that the substrate temperature is the key factor for fabricating high quality WZO thin films. The WZO thin films exhibit hexagonal wurtzite structure with (002) preferential growth orientation, and become more smooth at a much higher temperature. The optimized WZO thin film obtained at the substrate temperature of 300°C exhibits a high Hall mobility of 27.5cm2V−1s−1, a low sheet resistance of 23.3Ω/□, and an average transmittance of 82.0% in the wavelength range from 400 to 1500nm. The X-ray photoelectron spectroscopy (XPS) reveals that W element exists only in the oxidized state of W6+ in WZO thin films obtained at all the substrate temperatures, and Zn exists in a mixture state of oxidized and metallic formation.

Degenerate interface layers in epitaxial scandium-doped ZnO thin films

Scandium is a donor in ZnO, in contradiction to all heavier 3d-elements. Although the Sc3+ ion fits exactly the size of Zn2+, the conductivity of epitaxial Sc-doped ZnO thin films is dominated by a degenerated interface layer with pronounced Sc accumulation in the concentration depth profile. Electron paramagnetic resonance clearly excludes the isovalent oxidation state Sc2+ in ZnO, in agreement with the low resistivity of homoepitaxial ZnO : Sc of 1.3 × 10−2 Ω cm and high Hall mobility of 139 cm2 V−1 s−1 at 300 K. Employing the two-layer Hall model of Look and Molnar, a maximum Hall mobility of the volume part of the ZnO : Sc layer of 650 cm2 V−1 s−1 at 95 K was extracted. Thermal activation energies of the donors are 28 and 43 meV for a homoepitaxial ZnO : 0.1% Sc film. Homoepitaxial ZnO films with 0.1 and 1 at% Sc on c-plane ZnO are almost phase pure and in-plane lattice matched with perpendicular compressive strain up to 1%. Heteroepitaxial ZnO : Sc on a-plane sapphire shows secondary XRD peaks, pointing to a limited solubility of Sc in ZnO.

Structural and electrical properties of sputtering power and gas pressure on Ti-dope In2O3 transparent conductive films by RF magnetron sputtering

Transparent conductive titanium-doped indium oxide (ITiO) films were deposited on Corning glass substrates by RF magnetron sputtering method. The effects of RF sputtering power and Ar gas pressure on the structural and electrical properties of the films were investigated experimentally, using a 2.5wt% TiO2-doped In2O3 target. The deposition rate was in the range of around 20–60nm/min under the experimental conditions of 5–20mTorr of gas pressure and 220–350W of RF power. The lowest resistivity of 1.2×10−4Ωcm, the average optical transmittance of 75%, the high hall mobility of 47.03cm2/Vs and the relatively low carrier concentration of 1.15E+21cm−3 were obtained for the ITiO film, prepared at RF power of 300W and Ar gas pressure of 15mTorr. This resistivity of 1.2×10−4Ωcm is low enough as a transparent conducting layer in various electro-optical devices and it is comparable with that of ITO or ZnO:Al conducting layer.

Effect of Low-Temperature Microwave Processing and Copper Content on the Properties of Ag-Cu Thin Film Binary Alloys

The effects of Cu content on the electrical and structural properties of Ag-Cu thin films were studied before and after microwave processing. Copper was chosen as the alloying element because of its low solubility in Ag, which enables it to segregate at the surface. After microwave annealing, enhanced electrical and structural properties were observed. The results from Rutherford backscattering spectrometry, x-ray diffraction, and four-point probe measurements suggested that the resistivity is controlled by the residual copper concentration and increased grain growth during the low-temperature microwave anneals. For each particular copper concentration, microwave annealing resulted in highest Hall mobility and lowest resistivity. These findings opened the possibility for novel materials structures based on low-temperature microwave processing schemes.

Metamorphic InAlAs/InGaAs/InAlAs/GaAs HEMT heterostructures containing strained superlattices and inverse steps in the metamorphic buffer

Metamorphic InхAl1−хAs buffer design features influence on electrophysical and structural properties of the heterostructures was investigated. Two types of MHEMT heterostructures In0.70Al0.30As/In0.76Ga0.24As with novel design contained inverse steps or strained superlattices were grown by MBE on GaAs substrates. Electrophysical properties of the heterostructures were characterized by Hall measurements, while the structural features were described with the help of different transmission electron microscopy techniques. The metamorphic HEMT with strained superlattices inserted in the metamorphic buffer had the smoother surface and more defect-free crystal structure, as well as a higher Hall mobility, than metamorphic HEMT with inverse steps within the metamorphic buffer.

Annealing Effects on Electrical Properties of Pure and Tin-Doped Indium Oxide Thin Films

The annealing effects on the properties of ITO and pure In2O3 thin films have been investigated. The thin films were deposited with various O2 flow ratios to total gas flow by pulsed dc magnetron sputtering. The post-deposition annealing of the thin films was carried out for 30 minutes at various temperatures ranging up to 500 degrees C in air. It was found through the comparison of the carrier density of ITO and In2O3 thin films that the carrier electrons of the ITO thin films came from both of the dopant Sn and oxygen vacancies under the annealing less than 400 degrees C. Therefore, the ITO thin films deposited with lower O2 flow ratio exhibited higher carrier density due to many oxygen vacancies; in consequence, they exhibited lower resistivity at the annealing up to 400 degrees C. On the other hand, the carrier density of ITO thin films was almost identical regardless of O2 flow ratio when they were annealed at 500 degrees C. This fact indicates that most carrier electrons of the ITO thin films were brought by the dopant Sn at the annealing temperature of 500 degrees C. However, the ITO thin films deposited with lower O2 flow ratio exhibited higher Hall mobility; as a result, they showed lower resistivity at the annealing of 500 degrees C. Atomic force microscope, X-ray diffraction and X-ray reflectivity measurements revealed that the ITO thin films deposited with lowe O2 flow ratio exhibited dense structure even after they were annealed at 500 degrees C. Hence, the carrier electrons of the dense ITO thin films deposited with low O2 flow ratio can conduct better, as a result, the ITO thin films exhibited high Hall mobility and low resistivity.

Preparation and characteristics of Nb-doped indium tin oxide thin films by RF magnetron sputtering

Niobium-doped indium tin oxide (ITO:Nb) thin films are fabricated on glass substrates by radio frequency (RF) magnetron sputtering at different temperatures. Structural, electrical and optical properties of the films are investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), ultraviolet-visible (UV-VIS) spectroscopy and electrical measurements. XRD patterns show that the preferential orientation of polycrystalline structure changes from (400) to (222) crystal plane, and the crystallite size increases with the increase of substrate temperature. AFM analyses reveal that the film is very smooth at low temperature. The root mean square (RMS) roughness and the average roughness are 2.16 nm and 1.64 nm, respectively. The obtained lowest resistivity of the films is 1.2×10−4Ω·cm, and the resistivity decreases with the increase of substrate temperature. The highest Hall mobility and carrier concentration are 16.5 cm2/V·s and 1.88×1021cm−3, respectively. Band gap energy of the films depends on substrate temperature, which is varied from 3.49 eV to 3.63 eV.

Electrical, optical and etching properties of Zn-Sn-O thin films deposited by combinatorial sputtering

Zn-Sn-O (ZTO) films are known to be able to form an amorphous phase, which provides a smooth surface morphology as well as etched side wall, when deposited by using the conventional sputtering technique and, therefore, to have a potential to be applied as transparent thin film transistors. In this study, ZTO thin films were prepared by using combined sputtering of ZnO and SnO2 targets, and the dependences of their electrical and optical properties on the composition and the deposition parameters were examined. The Sn content in the films was varied in the range of 35 ∼ 85 at.%. The deposition was carried out at room temperature, 150 and 300 °C, and the oxygen content in sputtering gas was varied from 0 to 1 vol.%. Sn-rich films had better electrical properties, but showed large oxygen deficiency when deposited at low oxygen partial pressures. ZTO films with Sn contents lower than 55 at.% had good optical transmission, but the electrical properties were poor due to very low carrier concentrations. A high Hall mobility of larger than 10 cm2/Vs could be obtained in the carrier density range 1017∼1020 cm−3, and the etching rate was measurable for films with Sn content up to 70 at.% when using a dilute HCl solution, indicating a good possibility of utilizing ZTO films for device applications.

Effect of the substrate temperature on the structural, optical and electrical properties of spray-deposited CdS:B films

Boron doped CdS films have been deposited by spray pyrolysis method onto glass substrate temperature in the range of 350–450 °C. And the effect of substrate temperature (Ts) on the structural, electrical and optical properties of the films were studied. The structural properties of boron doped CdS films have been investigated by (XRD) X-ray diffraction techniques. The X-ray diffraction spectra showed that boron doped CdS films are polycrystalline and have a hexagonal (wurtzite) structure. By using SEM analysis, the surface morphology of the films was observed as an effect of the variation of substrate temperature. The substrate temperature is directly related with the shift detected in the band gap values derived from optical of parameters and the direct band gap values were found to be in the region of 2.08–2.44 eV. The electrical studies showed that the film deposited at the substrate temperature 400 °C had high carrier concentration and Hall mobility and minimum resistivity. This resistivity value decreased with increase in temperature up to 400 °C indicating the semiconducting nature of B- doped CdS films. The lattice parameter, grain size, microstrain and dislocation densities were calculated and correlated with the substrate temperature (Ts).

Near infrared enhancement in CIGS-based solar cells utilizing a ZnO:H window layer

We investigated the near infrared enhancement in Cu(In,Ga)Se(2) (CIGS)- based solar cells utilizing a hydrogen-doping ZnO (ZnO:H) window layer. The results show that the carrier concentration of ZnO:H film is lower than that of AZO film which can increase the transmittance in the NIR. The advantage of ZnO:H film is higher Hall mobility than AZO film. Thus ZnO:H film has similar resistivity to AZO film. It was found that the cell efficiency was 12.4 and 13% for the AZO device and the ZnO:H device, respectively. The cell efficiency is enhanced by 4.8%. Furthermore, the results indicate that, the ZnO:H film is superior to the AZO film as the window layer for CIGS-based solar cells.

Electronic structure and linear magnetoresistance of the gapless topological insulator PtLuSb

The present work reports on the experimental investigation of electronic structure and transport properties of the proposed topological insulator PtLuSb. The electronic structure was investigated by means of polarization dependent hard x-ray photoelectron spectroscopy. The valence band spectra exhibit a linear behavior close to the Fermi energy, as is typical for massless electrons. The transport properties are similar to that of a gapless semiconductor with low carrier concentration. This compound also exhibits an exceptionally high Hall mobility. At low temperatures, the magnetoresistance changes linearly with the applied magnetic field, whereas it exhibits a quadratic nature at high temperatures. A tentative relation between linear magnetoresistance and high mobility is discussed.

The properties of transparent conducting molybdenum-doped ZnO films grown by radio frequency magnetron sputtering

Transparent conducting molybdenum-doped zinc oxide films are prepared by radio frequency (RF) magnetron sputtering at ambient temperature. The MoO3 content in the target varies from 0 to 5 wt%, and each film is polycrystalline with a hexagonal structure and a preferred orientation along the c axis. The resistivity first decreases and then increases with the increase in MoO3 content. The lowest resistivity achieved is 9.2×10−4 Ω·cm, with a high Hall mobility of 30 cm2·V−1·s1 and a carrier concentration of 2.3×1020cm−3 at an MoO3 content of 2 wt%. The average transmittance in the visible range is reduced from 91% to 80% with the increase in the MoO3 content in the target.

Influence of the deposition temperature on electronic transport and structural properties of radio frequency magnetron-sputtered Zn1-xMgxO:Al and ZnO:Al films

Abstract

Hall mobility and characteristics of gas-phase polymerized poly(3-iodothiophene) thin films

The semi-conductive poly(3-iodothiophene)(P3IT) films were fabricated by gas-phase polymerization through a chemical vapor deposition process. The P3IT nanoscale films have a high crystalline morphologies, and possessed a high Hall mobility up to 10 cm2/Vs. The degree of crystalline and the mobility values measured through Scanning Electron Microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy with structural analysis. These conductive thin films, possessing polycrystalline structures, have a very high mobility and are capable of being applied to organic electronic layers for electrical devices such as the thin film transistors and organic photovoltaic cells.

Temperature-dependant growth and properties of W-doped ZnO thin films deposited by reactive magnetron sputtering

W-doped ZnO (WZO) thin films for thin film solar cells have been deposited by pulsed direct-current reactive magnetron sputtering. The microstructures, surface morphologies, optical and electrical properties of WZO thin films are investigated at different substrate temperatures. The experimental results indicate that a proper substrate temperature is the key factor for fabricating high-quality WZO thin films. The surface roughness of WZO thin films increases firstly from 15.65 nm to 37.60 nm, and then decreases from 37.60 nm to 11.07 nm with the increase of substrate temperature. Higher Hall mobility deposited at the higher temperatures is attributed to the compact structure and good crystallization quality. The WZO thin film prepared at the temperature of 325 ℃ presents excellent optical and electrical properties with an average transmittance of 85.7% in the wavelength range from 400 nm to 1500 nm, a low resistivity of 9.25× 10-3 Ω·cm, a sheet resistance of 56.24 Ω /sq and a high Hall mobility of 11.8 cm2·V-1·s-1.

Preparation of Al-doped ZnO transparent electrodes suitable for thin-film solar cell applications by various types of magnetron sputtering depositions

In order to determine the influence of different types of magnetron sputtering (MS) depositions on the characteristics of Al-doped ZnO (AZO) thin films appropriate for applications as transparent electrodes in thin-film solar cells, transparent conducting AZO thin films were prepared on glass substrates at 200 °C by direct current (dc) magnetron sputtering (dc-MS), radio frequency (rf)-MS and rf power superimposed dc-MS (rf + dc-MS) depositions using an MS apparatus with the same AZO target. AZO thin films prepared by an rf + dc-MS deposition exhibited both a higher deposition rate than that found with rf-MS depositions and a lower resistivity or higher Hall mobility than those found with dc-MS. The lower dc sputter voltage featured in rf-MS and rf ± dc-MS depositions, producing smoother surface morphology and better crystallinity than obtained with dc-MS depositions. The light scattering characteristics of surface-textured AZO thin films prepared by various types of MS depositions were evaluated by observing the surface texture and measuring the optical transmittance and the diffusive component; wet-chemical etching of the thin film surface was performed in a 0.1% HCl solution. The obtainable haze property in the range from visible to near infrared in AZO films prepared by an rf + dc-MS deposition was markedly better than that obtained with dc-MS depositions.