eV For InSe Research Articles

Optical and Photosensitive Properties of Flexible n (p)-InSe/In2O3 Heterojunctions.

In this work, optical, including photoluminescence and photosensitivity, characteristics of micrometer-sized flexible n (p)–InSe/In2O3 heterojunctions, obtained by heat treatment of single-crystalline InSe plates doped with (0.5 at.%) Cd (Sn), in a water-vapor- and oxygen-enriched atmosphere, are investigated. The Raman spectrum of In2O3 layers on an InSe:Sn substrate, in the wavelength range of 105–700 cm−1, contains the vibration band characteristic of the cubic (bcc-In2O3) phase. As revealed by EDX spectra, the In2O3 layer, ~2 μm thick, formed on InSe:Cd contains an ~18% excess of atomic oxygen. The absorption edge of InSe:Sn (Cd)/In2O3 structures was studied by ultraviolet reflectance spectroscopy and found to be 3.57 eV and ~3.67 eV for InSe:Cd and InSe:Sn substrates, respectively. By photoluminescence analysis, the influence of doping impurities on the emission bands of In2O3:Sn (Cd) was revealed and the energies of dopant-induced and oxygen-induced levels created by diffusion into the InSe layer from the InSe/In2O3 interface were determined. The n (p)–InSe/In2O3 structures display a significantly wide spectral range of photosensitivity (1.2–4.0 eV), from ultraviolet to near infrared. The influence of Cd and Sn concentrations on the photosensitivity and recombination of nonequilibrium charge carriers in n (p)–InSe layers from the heterojunction interface was also studied. The as-obtained nanosized InSe/In2O3 structures are suitable for optoelectronic applications.

InSe Nanothin Film with Ar-Gas Low Vacuum Pressure

InxSe1-x(x = 0.4, 0.5, 0.6) thin films are deposited at room temperature on glass substrates with thickness ~500nm by thermal evaporation technique. The X-Ray diffraction analysis showed that both the as-deposited films In2Se3and InSe (x= 0.4 and 0.5) are amorphous in nature while the as-deposited film In3Se2is polycrystalline and the values of energy gap are Eg=1.44eV for In2Se3, Eg=1.16eV for InSe and Eg=0.78eV for In3Se2. The same technique used with insert Argon gas at pressure 0.1 mbar where InxSe1-x(x = 0.4, 0.5, 0.6) thin films are deposited at room temperature on glass substrates with thickness ~100nm. The X-Ray diffraction analysis showed that the as-deposited films In2Se3are amorphous in nature while the as-deposited film InSe and In3Se2are Nanocrystalline with grain size 33nm and 55nm respectively and the values of energy gap are Eg=1.55eV for InSe and Eg=1.28eV for In3Se2. The energy gap of InSe thin films increase with Argon gas assist and phases changes from amorphous and polycrystalline to nanostructure material by thermal vacuum deposition technique.

Structural characterizations and optical properties of InSe and InSe:Ag semiconductors grown by Bridgman/Stockbarger technique

Undoped InSe and Ag doped InSe (InSe:Ag) single crystals have been grown by using the Bridgman/Stockbarger method. The freshly cleaved crystals have mirror-like surfaces even without using mechanical treatment. The structure and lattice parameters of the undoped InSe and InSe:Ag semiconductors have been analyzed using a X-ray diffractometer (XRD), Scanning electron microscopy (SEM) and energy dispersive X-rays (EDX) techniques. It is found that the InSe and InSe:Ag crystals had hexagonal structure, and calculated lattice constants were found to be a=4.002Å and c=17.160Å for InSe and a=4.619Å and c=17.003Å for InSe:Ag. The crystallite sizes have been calculated to be 40–150nm for InSe and 75–120nm for InSe:Ag from the SEM results. Ag doping causes a significant increase in the XRD peak intensity. It has been observed from EDX results that InSe contains In=57.12%, Se=38.08% and O=4.81%, respectively. Absorption measurements have been carried out in InSe and InSe:Ag samples in the temperature range 10–320K with a step of 10K. The first exciton energies for n=1 were calculated as 1.328, 1.260eV in InSe and were 1.340, 1.282eV in InSe:Ag at 10K and 320K, respectively.

The formation of organic (propolis films)/inorganic (layered crystals) interfaces for optoelectronic applications

Propolis (honeybee glue) organic films were prepared from an alcoholic solution on the surfaces of inorganic layered semiconductors (indium, gallium and bismuth selenides). Atomic force microscopy (AFM) and X-ray diffraction (XRD) are used to characterize structural properties of an organic/inorganic interfaces. It is shown that nanodimensional linear defects and nanodimensional cavities of various shapes are formed on the van der Waals (VDW) surfaces of layered crystals as a result of chemical interaction between the components of propolis (flavonoids, aminoacids and phenolic acids) and the VDW surfaces as well as deformation interaction between the VDW surfaces and propolis films during their polymerization. The nanocavities are formed as a result of the rupture of strong covalent bonds in the upper layers of layered crystals and have the shape of hexagons or triangles in the (0001) plane. The shape, lateral size and distribution of nanodimensional defects on the VDW surfaces depends on the type of crystals, the magnitude and distribution of surface stresses. We have obtained self-organized nanofold structures of propolis/InSe interface. It is established that such heterostructures have photosensitivity in the infrared range h ν < 1.2 eV (the values of energy gap are 1.2 eV for InSe and 3.07 eV for propolis films at room temperature).

Absorption measurement and Urbach’s rule in InSe and InSe:Ho0.0025, InSe:Ho0.025 single crystals

Abstract InSe and InSe:Ho single crystals were grown by the Bridgman–Stockberger method. Ho rare earth element are added to the InSe crystal as rate of 0.0025 and 0.025 g. Absorption measurements have been investigated as a function of temperature and Ho concentration. The high Ho concentration caused an increasing of intensity in absorption spectra and shifted towards to longer wavelengths. On the other hand low Ho concentration caused a decreasing of intensity in absorption spectra and shifted towards to longer wavelengths too. At 10 K and 320 K, the first exciton energies were calculated as 1.35 and 1.308 eV for InSe, 1.327 and 1.243 eV for InSe:Ho 0.0025 , 1.333 and 1.245 eV for InSe:Ho 0.025 , respectively. The exponentially increasing of absorption tail are explained as an Urbach–Martienssen’s (U–M’s) tail for InSe, InSe:Ho 0.0025 and InSe:Ho 0.025 samples in the 10–320 K temperature range. The Urbach’s energy ( E u ) are increased in both InSe:Ho 0.0025 and InSe:Ho 0.025 samples. But increasing rate is higher in InSe:Ho 0.0025 than InSe:Ho 0.025 sample.

Urbach Tail and Optical Investigations of Gd Doped and Undoped InSe Single Crystals

Undoped InSe and Gd doped InSe (InSe:Gd) single crystals were grown by using the stockbarger method. Ingots had no cracks and voids on the surface. There was no process to polish and clean treatments at cleavage faces of these samples because of the natural mirror-like cleavage faces. Absorption measurements were carried out in InSe and InSe:Gd samples in the temperature range 10–320 K with a step of 10 K. The first exciton energies for n = 1 were calculated as 1.323, 1.239 eV in InSe and were 1.317, 1.235 eV in InSe:Gd at 10 K and 300 K, and the second exciton energies for n = 2 in InSe were calculated as 1.338, 1.328 eV and in InSe:Gd were 1.331, 1.321 eV at 10 K and 80 K, respectively. Binding energies of InSe and InSe:Gd were calculated as 20.0 and 18.0 meV, respectively. The direct band gaps are estimated as 1.343, 1.259 eV in InSe and 1.335, 1.253 eV in InSe:Gd at 10 and 300 K, respectively. The steepness parameters and Urbach energy for InSe and InSe:Gd samples increased with increasing sample temperature in the range 10–320 K.

Novel single­molecule precursor routes for the direct synthesis of InS and InSe quantum dots

Nanoparticles of InS and InSe capped with TOPO (tri-n-octylphosphine oxide) or nanoparticles of InSe capped with 4-ethylpyridine, which are close to mono-dispersed, have been prepared by a single-source route using tris(diethyldithiocarbamato)indium(III) or tris(diethyldiselenocarbamato)indium(III), respectively. The nanoparticles of InS and InSe both show quantum size effects in their optical spectra and the photoluminescence (PL) spectra show broad emissions due to the surface traps. Substantial blue shifts in the onset of absorption have been observed; 0.44 eV for InS and 1.60 eV for InSe. The X-ray diffraction (XRD) pattern of InS showed co-precipitation with TOPO and the crystalline particles turned powdery when studied by transmission electron microscopy (TEM). Selected area electron diffraction (SAED), X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies of the InSe nanoparticles show the hexagonal phase in the size range 5.8–7.0 nm. The crystallinity of the InSe nanoparticles was also evident from high resolution transmission electron microscopy (HRTEM), which gave well defined images of nanosize particles with clear lattice fringes.

XPS Study on the Chemical Shifts of Crystalline III–VI Layered Compounds

Core electron binding energies of GaS(β), GaSe( e ) and InSe(γ) with respect to the vacuum level have been obtained by measuring the onset of secondary electron emission in the X-ray photoelectron spectroscopy (XPS). The chemical shift for the least bound core level of cation is estimated to be 3.4 eV for GaS, 2.0 eV for GaSe and 1.7 eV for InSe with respect to the level of metal. The Madelung constant of each compound is calculated to be 1.44, 1.60 and 1.48, respectively. The ionicity is estimated to be about 0.46, 0.45 and 0.49, respectively. The magnitude of chemical shift is discussed on the basis of the electrostatic model which reflects two-dimensional crystal structure.

XPS Study on the Change of Surface Potential of GaSe and InSe Induced by Ar+ Sputtering

The changes of surface potential, directly induced by Ar ion sputtering, have been studied using X-ray photoelectron spectroscopy for both p-type GaSe and n-type InSe with no dangling bonds on the cleaved surface. Since the sputtering makes the surface metal-rich in these compounds, it is then predicted that the surface potential dramatically changes. The change of work function due to sputtering is obtained by measuring the emission spectrum of slow secondary electrons. It decreases from 5.7 eV to 5.3 eV in GaSe and increases from 4.5 eV to 5.0 eV in InSe. The magnitude of band bending due to sputtering is estimated from the shift of core levels. It is found that the band bends downwards by about 0.2 eV in GaSe and upwards by about 0.6 eV in InSe. These experimental results are explained in terms of the thin metallic layer and the interface states on the sputtered surface.

Electronic properties of the III-VI layer compounds GaS, GaSe and InSe

High-resolution reflectivity spectra of the layer compounds GaS, GaSe and InSe have been measured at RT between 4 and 32 eV by using synchroton radiation. The function (ħω)2 ε2 has been obtained by Kramers-Kronig analysis of the reflectivity spectra. Above 20 eV in GaS and GaSe and 17.5 eV in InSe the excitation of the Ga3d and In4d electrons, respectively, generates sharp structures associated with the density of states of the conduction bands, except for the first prominent peak (and its spin-orbit partner) that has been associated with a core exciton, the binding energy of which is (0.5 ± 0.2) eV in GaS and (0.3 ± 0.2) eV in GaSe, while in InSe the core exciton is not resolved from the In4d ionization continuum. The valence band excitations have been analysed in detail and the relevant structures have been associated with transitions beginning in deeper and deeper valence bands and terminating mostly in the lower groups of conduction bands.