Electrical and optical properties of MoSe2 films prepared by r.f. magnetron sputtering

The electrical resistivity of MoSe₂ films prepared by r.f. magnetron sputtering was measured between 300 and 10 K. The main sputtering parameter governing the physical properties of the films was found to be the substrate temperature T_sub. The room temperature resistivity of the as-sputtered films increased from $\text{1.7 × 10}{}^{-1}\text{Ω}\text{cm}$(T_sub = -70 °C) to $\text{1.4 × 10}{}^1\text{Ω}\text{cm}\text{(T}{}_{\mathrm{<mtext>sub</mtext>}}\text{= 150 °}\text{C}\text{)}$. A check of the thermo-electrical response showed that the majority charge carriers are holes except for films deposited at T_sub = 150 °C which are n type. Hall effect measurements indicated very low Hall mobilities (3–5 cm² V^-1 s^-1). Thermal annealing increased the room temperature resistivities by more than one order of magnitude for the specimens sputtered at a low substrate temperature. The optical properties were weakly influenced by the process conditions. The optical gap was determined to be 1.06 eV.     

Surface scattering effects in CdS thin films

A method, based upon the careful investigation of the dependence of the Hall coefficient on thickness, to determine the value of the mean surface scattering length λ is presented. Hall data presented for slowly deposited cadmium sulphide thin films indicate the relationship between λ and the carrier concentration. Data are also presented to exhibit the critical dependence of λ upon substrate temperature and deposition rate. The temperature dependence of the parameter λ/μ_b indicates the predicted $\text{T}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ relationship.     

Related structural,electrical and photoelectrical properties of vacuum-deposited GaP thin films

GaP thin films with thicknesses from 0.1 to 0.6 μm were prepared by the thermal evaporation of the compound GaP onto quartz substrates at temperatures from ambient temperature to 740 °C. The properties of the films depended strongly on substrate temperature and deposition rate. With increasing substrate temperature the film structure changed from amorphous to textured polycrystalline with a strong [100] texture. The temperature of the amorphous-to-crystalline transition depended on deposition rate and was found to be 360 and 400 °C for deposition rates of 2 and 10 Å s^-1 respectively. At these temperatures the electrical resistivity of the films fell sharply from 10⁸ Ω cm to a minimum value of $\text{5 × 10}{}^4\text{Ω}\text{cm}$, after which it increased again with increasing temperature. The amorphous films exhibited a moderate photosensitivity with a maximum value near the temperature of the structural transition; above this temperature the films lost their photosensitivity completely. The spectral dependence of the photoconductivity was measured and an attempt was made to interpret the observed spectra.     

Reactive ion plating of metal oxides onto insulating substrates

SnO₂ and In₂O₃ films were produced by evaporation and by magnetron sputtering of the elements in an atmosphere containing oxygen. The insulating substrate of glass or plastic was water cooled and made one electrode of an r.f. discharge in the gas. The optical and electrical properties of the films indicated that the energy of the bombarding ions, measured by the d.c. standing voltage that developed on the substrate due to r.f. discharge, gave properties that had only previously been obtained using substrate temperatures of 450°C and above.The SnO₂ films were insulating. The In₂O₃ films were conducting, a minimum value of the sheet resistivity ($\text{187 Ω}\text{□}$ being achieved with evaporated films at a bias of ?400 V and a value of $\text{630 Ω}\text{□}$ being obtained with sputtered films at a bias of ?160 V with a 30 vol.% O₂?70 vol.% Ar gas mixture. All films were about 80 nm thick. The ultraviolet absorption edge position proved to be related to the refractive index and the conductivity. Hall effect measurements gave a carrier concentration of 4 × 10²⁵ m^?3 with a mobility of 1.9 × 10^?3 m² V^?1 s^?1 for the best sputtered film.     

Crystallography of epitaxially grown molybdenum on sapphire

Molybdenum thin films were deposited onto (0001), ($\text{1012}$) and (10$\text{12}$) sapphire substrates by electron-beam evaporation in ultrahigh vacuum. The surface morphology and crystallographic orientation of these films were characterized by electron microscope replication and reflection electron diffraction. The effect of the crystallographic plane of the sapphire substrates as well as that of the deposition rate on the crystallographic orientation of the deposited molybdenum films were examined in the temperature range 25°-1000°C. The epitaxial temperature range was 600°-900°C for basal plane substrates and 300°-1000°C for ($\text{1}$012) and (10$\text{1}$2) substrates. The orientation of the deposited film was strongly dependent on that of the sapphire substrate.     

Effects of substrate temperature on tin-doped indium oxide films deposited by dc arc discharge ion plating

Indium tin oxide (ITO) films were deposited on glass substrate at temperatures ranging from room temperature to 120 °C by the dc arc discharge ion plating technique. The electrical properties and crystallinity of ITO films were investigated. The resistivity of ITO films decreased with the increase of the substrate temperature in deposition, mostly due to increase in Hall mobility above 90 °C. The resistivity of ITO film obtained at temperature 120 °C was 1.33×10⁻⁴ Ω cm. The ITO films crystallized at the substrate temperature higher than 90 °C and the grain size estimated from the (2 2 2) peak in the direction parallel to the surface of the substrate became large with the increase of the substrate temperature. That the Hall mobility increased with the increase of the substrate temperature was speculated to be due to the increase of the grain size in the direction parallel to the surface.     

Structural,electrical and optical properties of r.f.-magnetron-sputtered SnO2:Sb film

The effects of gas composition, pressure and substrate temperature on the properties of relatively thick (0.2–0.8 μm) SnO₂ films deposited onto fused quartz substrates by r.f. magnetron sputtering are reported. The lowest resistivity of about 2 × 10^?3ωcm was attained for high rate deposition conditions of about $\text{1000}\text{A}\text{?}\text{min}{}^{\mathrm{?1}}$ on substrates at a temperature of 400°C in an atmosphere of 10% O₂. This value corresponds to a carrier density of 3 × 10²⁰cm^?3 and a mobility of 10 cm²V^?1s^?1. The crystal structure was found to be sensitive to all the above parameters. Low resistivity films showed a highly preferred orientation of (101) parallel to the substrate.     

Direct synthesis of epitaxial zinc sulphide layers on zinc single-crystal substrates

Epitaxial thin zinc sulphide layers have been grown by direct synthesis on the basal face of zinc single crystals. Sulphur vapour reacted on the surface of the crystals, which were grown in sealed glass ampoules evacuated to 10^?6 torr. The thicknesses of the layers investigated varied from several hundred to 1000–1500 Å. The morphology, structure and epitaxy of the films were examined by electron microscope, electron and X-ray diffraction techniques. It was found that the film lattice had a sphalerite-type cubic structure, the perfection of the layer structure increasing with rise in both the substrate temperature and the sulphur vapour pressure. The layers were produced at substrate temperatures of 250°–400°C: polycrystalline ZnS films were obtained in the range 250°–300°C; at higher temperatures a definite texture gradually appeared and above 370°C, with a sulphur vapour pressure of 0.2–10 torr, the films became epitaxial. The following epitaxial relation was established:

$\text{{111} ZnS ∥ {0001} Zn}$

with

$\text{<110 > ZnS ∥ <11}\text{20}\text{> Zn}$

The zinc sulphide films reproduced the surface structure of the supporting zinc single crystals very well and could conveniently be used as electron microscope replicas.     

Amorphous chromium-silicon: A material for kilo-ohm sheet resistances

On investigating the relationship between the composition, structure and electrical properties of sputtered Cr-Si films we found a highly stable material (mole fraction of silicon, 57 ± 7%) with a resistivity of $\text{580 ± 50 μΩ}\text{cm}$ and a temperature coefficient of resistivity (TCR) of -80 to -130 ppm K^-1.Using the same target but with a substrate temperature during deposition of about 400°C and with an oxygen partial pressure of about 10^-1 N m^-2, it was possible to produce films with a resistivity of up to 11 000 μΩ cm and with a TCR of less than -300 ppm K^-1. Electron diffraction patterns of the films showed an amorphous structure.To confirm the stability and reproducibility of the material several hundred films (thickness, 28 nm) were produced. The change ΔR/R in the resistance of these films (without preheating in air and without using a protective layer) after annealing in air at 150°C for 250 h was less than 1%.     

Structural and electrical properties of RuO2 thin films prepared by rf-magnetron sputtering and annealing at different temperatures

Conductive ruthenium oxide (RuO₂) thin films have been deposited at different substrate temperatures on various substrates by radio-frequency (rf) magnetron sputtering and were later annealed at different temperatures. The thickness of the films ranges from 50 to 700 nm. Films deposited at higher temperatures show larger grain size (about 140 nm) with (200) preferred orientation. Films deposited at lower substrate temperature have smaller grains (about 55 nm) with (110) preferred orientation. The electrical resistivity decreases slightly with increasing film thickness but is more influenced by the deposition and annealing temperature. Maximum resistivity is 861 μΩ cm, observed for films deposited at room temperature on glass substrates. Minimum resistivity is 40 μΩ cm observed for a thin film (50 nm) deposited at 540°C on a quartz substrate. Micro-Raman investigations indicate that strain-free well-crystallized thin films are deposited on oxidized Si substrates.     

Structure and properties of highly crystallized graphite films based on polyimide Kapton

Highly crystallized graphite films were prepared by heat treatment of carbonized polyimide films (Kapton) at temperatures of 2700 and 3050° C. Interlayer spacing d ₀₀₂ at room temperature, and electrical resistivity, magnetoresistance and Hall coefficient at room and liquid nitrogen temperatures were measured. All of these data indicate high crystallinity of the graphitized Kapton films obtained. For the graphite films heat treated at 3050° C mean-square mobilities were estimated from the magnetoresistance data at 1 T to be 0.91 m² V^–1 sec^–1 at room temperature and 2.3 m² V^–1 sec^–1 at liquid nitrogen temperature; the value at liquid nitrogen temperature corresponds to that for a pyrolytic graphite heat treated at 3200° C for 1 h (PG 3200). Magnetic field dependence of Hall coefficient at liquid nitrogen temperature for this sample also agrees well with that for PG 3200. Scanning electron micrographs on the surfaces show that the present graphite films consist of grains of large crystallites, and grain size increases as the crystallinity of the material improves.     

The structure and semiconducting properties of cadmium selenide films

CdSe films about 1 μm thick were vacuum deposited on unheated glass substrates. Reflection electron diffraction studies showed the growth of a one-dimensional {00.1} texture orientation of the hexagonal phase. Films of lower resistivity were characterized by a larger grain size and better ordering, whilst films of higher resistivity contained amorphous regions and were less ordered. A study of the carrier type, the concentration, the Hall mobility and the variation in the bond length u along the hexagonal c axis of “as-deposited” and heat-treated films showed that the lower resistivity films incorporated a small cadmium excess, which increased with heat treatment, resulting in higher carrier concentrations and a further lowering of the resistivity. Large increases in the resistivities of films deposited at high rates were attributed to the depletion of the small individual grains.     

The influence of annealing on the resistivity and the thermoelectric power of evaporated palladium films

Palladium films in the thickness range from 5 to 60 nm were evaporated at 80 K and annealed at various temperatures up to 440 K. The resistivity and the thermoelectric power of the films were measured as functions of the thickness, the annealing temperature and the measuring temperature. It is necessary to use annealing temperatures as high as 400–440 K in order to obtain films in which the resistivity $\text{(?}{}_0\text{(280}\text{K}\text{) = 11.5 μΩ}\text{cm}\text{)}$ and the thermoelectric power (S₀(280 K) = ?9.3 μV K^?1) approach, when extrapolated to infinite thickness, the values of well-ordered bulk palladium (? = 10.03 μΩ cm, S = ?9.30 > μV K^?1 at 280 K).     

Interdiffusion and phase formation in Au/Sn thin film couples with special emphasis on substrate temperature during condensation

The interdiffusion of gold and tin thin films was studied, with special emphasis on the influence of the substrate temperature during evaporation. A special target chamber makes it possible to evaporate several films in succession and to analyse them by Rutherford backscattering at any stage in the interdiffusion process without exposing the specimens to the atmosphere. The samples can be kept at any temperature between -170 and +150°C during the evaporation, the heat treatment and the analysis. The interdiffusion of Au/Sn films is complex, with several competing processes going on at the same time. If the tin is evaporated at low temperatures, the initial stage of the interdiffusion will be dominated by grain boundary diffusion of gold into the tin film followed by diffusion into the tin grains, resulting in the formation of the AuSn₄ phase. The growth of the AuSn₄ phase was found to be linear with time. Concurrently the AuSn phase grows in a planar manner from the original interface. The thickness of this phase grows as t$\text{1}\text{2}$ and is believed to be limited mainly by the grain boundary diffusion of gold through the AuSn phase. This diffusion has an activation energy E_a = 0.59±0.06eV. When the substrate temperature during evaporation of the tin film is decreased, we observe an increase in the growth rate of the AuSn phase. This is believed to be caused by the decrease in grain size.     

Properties of polycrystalline silicon grown on insulating substrates by electron beam gun evaporation

Growth of polycrystalline silicon on insulating substrates such as glass, silicon dioxide and fused quartz was studied using an electron beam gun evaporation technique. Growth characteristics were studied as a function of substrate temperature. The results of scanning electron microscopy, secondary ion mass spectrometry and X-ray diffraction studies on various films are presented. Hall mobility, resistivity and carrier concentration measurements are also presented. Growth of polycrystalline films (as determined by X-ray diffraction studies) on glass substrates at as low a temperature as 525 °C were observed. Below this substrate temperature, films became amorphous. The grain size increased with the increase in the substrate temperature. The highest value of the Hall mobility measured was about 10 cm² V⁻¹ s⁻¹. Both n-type and p-type films were obtained.     

Substrate temperature dependent structural,optical, morphology and electrical properties of RF sputtered CdTe thin films for solar cell application

In this work, we have studied the influence of substrate temperature on structural, morphology optical, and electrical properties of CdTe thin films deposited by RF magnetron sputtering. Films were analyzed by using variety of techniques such as low angle X-ray Diffraction, UV–Visible spectroscopy, Raman spectroscopy, Field emission scanning electron microscopy (FE-SEM), Energy-dispersive X-ray spectroscopy (EDAX) Hall Measurement etc. Low angle XRD analysis showed that CdTe films are polycrystalline and has cubic structure with preferred orientation is along (111) direction. Raman scattering studies revealed the presence of single phase CdTe over the entire range of substrate temperature studied. The FE-SEM analysis showed that CdTe growth process occurred predominantly by grain growth and not through the layer-by-layer mode. Compositional analysis carried out using EDAX suggests that CdTe films deposited at low substrate temperatures are Te rich and that at higher temperatures is Cd rich. Electrical resistivity of CdTe films decreases with increase in substrate temperature and whereas positive increase in Hall coefficient suggests as-deposited CdTe films are p-type. The UV–Visible spectroscopy analysis showed that the band gap increases from 1.47 to 1.51 eV when the substrate temperature increased from 50 to 300 °C. Such optimum band gap CdTe can be use as absorber material in photovoltaic applications like the CdS/CdTe and ZnO/CdTe solar cells.     

Electrical effects of thallium on the Hall mobility in p-PbTe thin films

The Hall coefficient and Hall mobility were measured for epitaxial p-type PbTe films doped with thallium. It was observed that doping of the films with thallium leads to a decrease in the mobility and an increase in the concentration of charge carriers. The mobility μ_D limited by defect scattering was calculated and was found to be independent of temperature and to decrease with increases in the carrier concentration p. For films with carrier concentrations exceeding 7 × 10¹⁸ cm^-3 the value of μ_D decreases as p^{-$\text{4}\text{3}$}, whereas for films with lower carrier concentrations the decrease in μ_D with p is at a slower rate.     

Low temperature annealing behavior of electroplated nickel

The low temperature annealing characteristics of electroplated nickel containing an occluded brightener, fuchsin, have been studied in the temperature range 25–250°C. Supportive annealing experiments were also conducted between the temperatures 250°C and 700°C to assist in evaluating the lower temperature behavior. The effect of annealing was monitored by measuring resistivity changes at liquid nitrogen temperatures and by viewing selected samples by transmission electron microscopy. In addition, various chemical analysis techniques were employed to follow the variations in impurity content.A detailed comparison was made between deposits from a standard “watts” nickel electrolyte and those from a “watts” nickel solution containing the fuchsin additive. Isochronal anneals of fuchsin-containing deposits were characterized by a large decrease in resistivity up to a temperature of 175°C. Higher temperature annealing from 175°C to 275°C demonstrated an increase in resistivity with increasing temperature. This increase was then followed by a general decrease in resistivity at temperatures greater than 350°C. The first two minima at 175°C and 300°C on the Δ?°/Δ? versus temperature curve were found to coincide with temperatures where partial decomposition of the fuchsin reagent occured.The low temperature resistivity decrease from 28°C to 125°C was attributed to the diffusion of divacancies to fixed sinks such as grain boundaries. A high non-equilibrium vacancy concentration is believed to be present owing to the accommodation of fuchsin molecules in the nickel lattice. The resistivity decay is described by an Arrhenius-type equation:

$\text{dp}\text{dt}\text{=K exp}\text{?}\text{19.4 kcal}\text{RT}$

The experimentally determined activation energy agrees favorably with literature values for divacancy diffusion in nickel. During this interval no visual change in structure was noted, and fuchsin could be extracted from the deposit unaltered.     

The structure of nickel and cobalt films on the (111) surface of n-type silicon

Films of Ni and Co have been grown on the (111) surface of phosphorus doped n-type silicon by evaporation in high vacuum. For both systems polycrystalline films resulted for all substrate temperatures except in the range 250° to approximately 400°C when f.c.c. Ni or Co grew with the orientation Ni/Co (110)6Si (111); Ni/Co [$\text{1}$10]6Si [$\text{2}$11].     

Interdiffusion of thin Cr and Au films deposited on silicon

The backscattering technique has been used to study the interdiffusion process of Cr and Au films deposited on silicon substrates. The results indicate that Au diffuses in Cr with an effective diffusion coefficient $\text{D =}\text{const. exp}\text{(?0.68/}\text{k}\text{T)}$. The activation energy is consistent with a diffusion process which occurs preferentially through grain boundaries. The high value of the diffusion coefficient justifies the presence of Au at the CrSi interface after a low temperature short-time heat treatment. At temperatures above 370 °C (the eutectic point of the SiAu system) and after a long enough heat treatment the gold is completely mixed with silicon.