Structural, optical and electrical properties of indium nitride polycrystalline films

The structural, optical and electrical properties of InN polycrystalline films on glass substrate are investigated by means of X-ray photoelectron spectroscopy, Raman scattering measurements, X-ray diffraction analysis, optical spectroscopy, and electrical measurements as a function of the inverse of temperature. The absorption edge for the films is most likely due to an impurity band formed by the presence of defects in the material. Such an impurity band, located at 1.6 eV extends itself to about 1.8 eV above the Fermi level, and it is attributed to nitrogen vacancies present in the material. The Raman scattering data also reveal the incorporation of oxygen in the InN films, leading to the formation of the In₂O₃ amorphous phase during the process of sputtering. Additionally, the X-ray photoelectron spectroscopy of the valence band, which is highly desirable to the determination of the Fermi level, confirms the optical gap energy. Furthermore, the X-ray diffraction patterns of the thinner films present broader peaks, indicating high values for the strain between the film lattice and the glass substrate. Finally, first principles calculations are used to investigate the optical properties of InN and also to support the experimental findings.     

Structure and bandgap determination of InN grown by RP-MOCVD

InN thin films are grown on sapphire substrates by remote plasma-assisted metal organic chemical vapor deposition while varying the indium pulse length and substrate temperature. The effects of the indium pulse length and temperature on the structural, morphological, electronic, and optical properties of the thin films are studied. The structural parameters are determined by X-ray diffraction and X-ray photoelectron spectroscopy and the effects of incorporating oxygen atoms in the structure is described. The N K-edge X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) measurements are used to determine the band gap and it is found to be 1.80?±?0.25 eV for all samples. A complementary measurement namely, X-ray excited optical luminescence measurement is performed to confirm the band gap value obtained from XAS and XES measurements. O K-edge XAS measurements are performed to determine the presence of oxygen impurities in the samples. Meanwhile, we carry out the density functional theory calculations for Wurtzite InN, hypothetical Wurtzite-type InO_0.5N_0.5, and InO_0.0625N_0.9375 structures. We find that the measured N-edge spectra agree well with our Wurtzite InN calculations and the measured O K-edge spectra agree better with hypothetical Wurtzite-type InO_0.0625N_0.9375 than Wurtzite-type InO_0.5N_0.5.

     

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).     

Optical and structural properties of CuSbS2 thin films grown by thermal evaporation method

Structural, optical and electrical properties of CuSbS₂ thin films grown by thermal evaporation have been studied relating the effects of substrate heating conditions of these properties. The CuSbS₂ thin films were carried out at substrate temperatures in the temperature range 100-200 °C. The structure and composition were characterized by XRD, SEM and EDX. X-ray diffraction revealed that the films are (111) oriented upon substrate temperature 170 °C and amorphous for the substrate temperatures below 170 °C. No secondary phases are observed for all the films. The optical absorption coefficients and band gaps of the films were estimated by optical transmission and reflection measurements at room temperature. Strong absorption coefficients in the range 10⁵-10⁶ cm^− 1 at 500 nm were found. The direct gaps Eg lie between 0.91-1.89 eV range. It is observed that there is a decrease in optical band gap Eg with increasing the substrate temperature. Resistivity of 0.03-0.96 Ω cm, in dependence on substrate temperature was characterized. The all unheated films exhibit p-type conductivity. The characteristics reported here also offer perspective for CuSbS₂ as an absorber material in solar cells applications.     

Structural,optical and microscopic properties of chemically deposited Mo<Subscript>0.5</Subscript>W<Subscript>0.5</Subscript>Se<Subscript>2</Subscript> thin films

Mo_0.5W_0.5Se₂ thin films were obtained by using relative simple chemical route at room temperature. Various preparative conditions of the thin films are outlined. The films were characterized by X-ray diffraction, scanning electron microscope, optical and electrical properties. The grown films were found to be uniform, well adherent to substrate and brown in color. The X-ray diffraction pattern shows that thin films have a hexagonal phase. Optical properties show a direct band gap nature with band gap energy 1.44 eV and having specific electrical conductivity in the order of 10⁻⁵ (Ωcm)⁻¹.     

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.     

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.     

Influence of indium concentration on the structural and optoelectronic properties of indium selenide thin films

We have grown indium selenide thin films using magnetron sputtering method. The influence of indium concentration on the structural, optical and electrical properties was studied. The concentration of indium in indium selenide thin films was varied by adjusting the sputtering power from 40 to 80 W while keeping the substrate temperature and argon pressure constant. The β-phase, which only exists at elevated temperatures in bulk single crystals, can persist at room temperature in the In-rich films. The β-phase thin film with smaller band gap has an electrical resistivity about four orders of magnitude lower than that of the γ-In₂Se₃ thin film, which is also stable at room temperature. Furthermore, the single-phase γ-In₂Se₃ thin film was then assembled in visible-light photodetector which shows a fast, reversible, and stable response. These results indicate the possibility of using γ-In₂Se₃ thin film in various next-generation photoelectric and optical-memory applications.     

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.     

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.     

Bismuth alloying in GaAs: a first-principles study

We present a theoretical study mainly devoted to the investigation of the bowing parameter in the GaAs_1–xBi_x alloy. Results reveal that the fundamental band gap for GaAs is close to 0.08 eV and it corresponds to −2.01 eV for GaBi. The addition of Bi to GaAs serves to make the lattice constant of the crystal larger than GaAs and distorts the valence band. This causes an intrinsic asymmetry between the carrier mobility. The band gap of GaAsBi alloy decreases with increasing Bi content. Moreover, the non-linear variation of the lattice parameter is clearly visible with upward bowing parameter, equal to −0.378 ± 0.16 Å. Compared with preceding works on the matter, the band gap versus composition is well fitted with a downward bowing parameter of 1.74 ± 0.51 eV. This shows that the direct band gap of this alloy covers a spectral region ranging from near infrared to infrared.     

Substrate bias voltage influenced structural, electrical and optical properties of dc magnetron sputtered Ta2O5 films

Tantalum oxide (Ta₂O₅) films were formed on silicon (111) and quartz substrates by dc reactive magnetron sputtering of tantalum target in the presence of oxygen and argon gases mixture. The influence of substrate bias voltage on the chemical binding configuration, structural, electrical and optical properties was investigated. The unbiased films were amorphous in nature. As the substrate bias voltage increased to −50 V the films were transformed into polycrystalline. Further increase of substrate bias voltage to −200 V the crystallinity of the films increased. Electrical characteristics of Al/Ta₂O₅/Si structured films deposited at different substrate bias voltages in the range from 0 to −200 V were studied. The substrate bias voltage reduced the leakage current density and increased the dielectric constant. The optical transmittance of the films increased with the increase of substrate bias voltage. The unbiased films showed an optical band gap of 4.44 eV and the refractive index of 1.89. When the substrate bias voltage increased to −200 V the optical band gap and refractive index increased to 4.50 eV and 2.14, respectively due to the improvement in the crystallinity and packing density of the films. The crystallization due to the applied voltage was attributed to the interaction of the positive ions in plasma with the growing film.     

Optical band gap of Sn<Subscript>0.2</Subscript>Bi<Subscript>1.8</Subscript>Te<Subscript>3</Subscript> thin films

Sn_0.2Bi_1.8Te₃ thin films were grown using the thermal evaporation technique on a (001) face of NaCl crystal as a substrate at room temperature. The optical absorption was measured in the wave number range 500–4000 cm⁻¹. From the optical absorption data the band gap was evaluated and studied as a function of film thickness and deposition temperature. The data indicate absorption through direct interband transition with a band gap of around 0.216 eV. The detailed results are reported here.     

Influence of substrate temperature on structural,optical, and electrical properties of flash evaporated CuIn0.81Al0.19Se2 thin films

Chalcopyrite copper indium aluminum diselenide (CuIn_0.81Al_0.19Se₂) compound is prepared by direct reaction of high purity elemental copper, indium, aluminum and selenium in their stoichiometric proportion. Structural and compositional characterizations of pulverized material confirm the formation of a single phase, polycrystalline nature. CuInAlSe₂ (CIAS) thin films are deposited on organically cleaned soda lime glass substrates using flash evaporation technique by varying the substrate temperatures in the range from 423 K to 573 K. Influence of substrate temperature observed by X-ray diffraction (XRD), scanning electron microscope (SEM), optical and electrical measurement. CIAS Films grown at different substrate temperatures are polycrystalline in nature, exhibiting a chalcopyrite structure with lattice parameters a = ∼0.576 nm and c = ∼1.151 nm. The crystallinity in the films increases with increasing substrate temperature up to 473 K, and tend to degrade at higher substrate temperatures. Optical band gap is in the range of 1.20 eV–1.38 eV and the absorption coefficient is close to 10⁵ cm⁻¹. Electrical characterization reveals p-type conductivity and the structural, morphological and optical properties indicate potential use of CIAS thin films as an absorber layer for thin film solar cell applications.     

Effect of deposition conditions on the InP thin films prepared by spray pyrolysis method

InP thin films were prepared by spray pyrolysis technique using aqueous solutions of InCl₃ and Na₂HPO₄, which were atomized with compressed air as carrier gas. The InP thin films were obtained on glass substrates. Thin layers of InP have been grown at various substrate temperatures in the range of 450–525°C. The structural properties have been determined by using X-ray diffraction (XRD). The changes observed in the structural phases during the film formation in dependence of growth temperatures are reported and discussed. Optical properties, such as transmission and the band gap have been analyzed. An analysis of the deduced spectral absorption of the deposited films revealed an optical direct band gap energy of 1.34–1.52 eV for InP thin films. The InP films produced at a substrate temperature 500°C showed a low electrical resistivity of 8.12 × 10³ Ω cm, a carrier concentration of 11.2 × 10²¹ cm⁻³, and a carrier mobility of 51.55 cm²/Vs at room temperature.     

Microstructure, optical and dielectric properties of compositional graded (Ba,Sr)TiO3 thin films derived by RF magnetron sputtering

Thin films of compositional graded Ba_1−x Sr _x TiO₃ (BST) (x decreasing from 0.3 to 0) were prepared on fused quartz and Pt/Ti/SiO₂/Si substrates by RF magnetron sputtering. The microstructure of the graded BST thin films was characterized by X-ray diffraction (XRD). It indicates that the films were crystallized with peroveskite structure and (100) + (111) preferred orientation. The refractive index and the band gap were determined at room temperature in the wavelength 200–1100 nm from spectrophotometric measurements of the transmittance. The average value of the refractive index is found to be 2.17 for the graded BST films in the wavelength 400–1000 nm. The optical band gap of the graded BST film was 3.77 eV. The dielectric measurement showed that the dielectric constant and loss factor of the graded BST film was 318.04 and 0.028 at 100 KHz and room temperature.     

Thickness dependent properties of nickel oxide thin films deposited by dc reactive magnetron sputtering

Nickel oxide thin films of various thicknesses were grown on glass substrates by dc reactive magnetron sputtering technique in a pure oxygen atmosphere with sputtering power of 150 W and substrate temperature of 523 K. Crystalline properties of NiO films as a function of film thickness were investigated using X-ray diffraction. XRD analysis revealed that (200) is the preferred orientation and the orientation of the films changed from (200) to (220) at film thickness of 350 nm. The maximum optical transmittance of 60% and band gap of 3.82 eV was observed at the film thickness of 350 nm. The lowest electrical resistivity of 5.1 Ω cm was observed at a film thickness of 350 nm, thereafter resistivity increases with film thickness.     

Structural,optical, and electrical properties of flash-evaporated copper indium diselenide thin films

Copper indium diselenide (CuInSe₂) compound was synthesized by reacting its elemental components, i.e., copper, indium, and selenium, in stoichiometric proportions (i.e., 1:1:2 with 5% excess selenium) in an evacuated quartz ampoule. Structural and compositional characterization of synthesized pulverized material confirms the polycrystalline nature of tetragonal phase and stoichiometry. CuInSe₂ thin films were deposited on soda lime glass substrates kept at different temperatures (300–573 K) using flash evaporation technique. The effect of substrate temperature on structural, morphological, optical, and electrical properties of CuInSe₂ thin films were investigated using X-ray diffraction analysis (XRD), atomic force microscopy (AFM), optical measurements (transmission and reflection), and Hall effect characterization techniques. XRD analysis revealed that CuInSe₂ thin films deposited above 473 K exhibit (112) preferred orientation of grains. Transmission and reflectance measurements analysis suggests that CuInSe₂ thin films deposited at different substrate temperatures have high absorption coefficient (~10⁴ cm⁻¹) and optical energy band gap in the range 0.93–1.02 eV. Results of electrical characterization showed that CuInSe₂ thin films deposited at different substrate temperatures have p-type conductivity and hole mobility value in the range 19–136 cm²/Vs. Variation of energy band gap and resistivity of CuInSe₂ thin films deposited at 523 K with thickness was also studied. The temperature dependence of electrical conductivity measurements showed that CuInSe₂ film deposited at 523 K has an activation energy of ~30 meV.     

Influence of substrate and selenization temperatures on the growth of Cu2SnSe3 films

The effects of substrate temperature and selenization temperature on the structure, composition, electrical and optical properties of Cu₂SnSe₃ films were studied systematically. Cu₂SnSe₃ films deposited at various substrate temperatures (303–573 K) by the flash evaporation method are found to be non-stoichiometric. To compensate the selenium deficiency and obtain a single-phase, an annealing Cu₂SnSe₃ films deposited at 573 K was performed in selenium atmosphere. Cu₂SnSe₃ films deposited at a substrate temperature of 573 K and then selenized at 673 K were single phase and polycrystalline exhibiting monoclinic structure. The films showed p-type conductivity with a direct band gap of 0.84 eV.     

Reflectance and photoluminescence spectra of as grown and hydrogen and nitrogen incorporated tetrahedral amorphous carbon films deposited using an S bend filtered cathodic vacuum arc process

The study of reflectance and photoluminescence (PL) spectra of as grown and also hydrogen and nitrogen incorporated tetrahedral amorphous carbon (ta-C) films, deposited using an S bend filtered cathodic vacuum arc process is reported here. First the effect of negative substrate bias on the properties of as grown ta-C films and next the effect of varying hydrogen and nitrogen partial pressure at a high substrate bias of − 300 V on the properties of hydrogen and nitrogen incorporated ta-C (ta-C:H and ta-C:N) films are reported for the first time. The values of the optical band gap (E_g) evaluated using the reflectance spectra were found to decrease with the increase of the substrate bias in the as grown ta-C films. Hydrogen incorporation up to 1.9 × 10^− 2 Pa partial pressure in as grown ta-C films increased the values of E_g and beyond which the values of E_g decreased while the nitrogen incorporation up to 3.0 × 10^− 1 Pa partial pressure has no effect on the E_g values. The PL spectra indicated a strong peak at ∼2.66 eV in as grown ta-C films deposited at − 20 V substrate bias. This main peak was found to shift to higher energy with the increase of the substrate bias up to − 200 V and thereafter the PL peak shifted towards the lower energy. Other peak at 3.135 eV starts appearing and this is found to start shifting to higher energy for films deposited at higher substrate bias. The intensity of the main PL peak was enhanced at low temperature and several other peaks started appearing in place of the broad peak at ∼3.16 eV. The peak width and area of both the main peak were found to decrease with the increase of substrate bias in as grown ta-C films and with the increase of the hydrogen and nitrogen partial pressure used in depositing ta-C:H and ta-C:N films. The current models on the source of luminescence in amorphous carbon have been discussed.