Direct Vapour Transport Technique Research Articles

Low temperature anisotropic photoresponse study of bulk ZrS3 single crystal

The present work shows zirconium trisulphide (ZrS3) single crystals-based photodetector functionality synthesized through the Direct Vapor Transport (DVT) technique. The elemental-chemical, surface morphology, structural phase, crystallinity and vibrational modes of the crystals were analyzed using Energy Dispersive Analysis of X-rays (EDAX), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Raman Spectroscopy respectively. These characterizations revealed the pure and layered crystals grown having a monoclinic phase with good crystallinity. Time-dependent photo-response of the detector fabricated from ZrS3 single crystals possessing smooth surface was recorded under the illumination of white light for different incident illumination levels (20 mW/cm2 to 120 mW/cm2) at room temperature. Further, a low-temperature photo-response upto 100 K for the incident light intensity of 120 mW/cm2 was carried out to validate the stability and durability of the detector. Typical detector parameters like responsivity, detectivity, sensitivity and response times were calculated and their variations are studied thoroughly concerning incident intensity and low-temperature. Furthermore, owing to the layered structure of the material, the photo-response of the device was recorded in both parallel (⊥to c-axis) and perpendicular (║to c-axis) direction of the crystallographic b-axis and device parameters were calculated at the room as well as low temperatures. The device exhibited strong anisotropy that originated from the layered structure of the grown crystals and involved an anisotropic charge conduction mechanism at the room as well as low temperatures.

Enhanced electrical and optoelectronic performance of SnS crystal by Se doping

In the current decade, Metal chalcogenides have achieved immense importance due to their tunable bandgaps, excellent optical absorption and outstanding optoelectronic behavior. Specifically, pristine and doped SnS (tin sulfide) crystals have fascinated noteworthy consideration mainly due to their potential applications in photodetectors, photovoltaic devices, holographic recording devices and field-effect transistors. In that view, selenium doped tin sulfide crystals were synthesized by direct vapor transport (DVT) technique. The elemental composition was confirmed by energy dispersive analysis of X-ray (EDAX). The structural characterization reveals a layer type growth mechanism of grown SnS0.25Se0.75 crystals. The powder X-ray diffraction reveals the orthorhombic phase and high crystallinity of synthesized crystals. X-ray photoelectron spectroscopy analysis confirmed the formation of SnS0.25S0.75 structure and binding energy of the elements in the samples. The temperature dependent in-plane and out-of-plane resistivity measurements determined the anisotropic charge conduction of grown crystals. The carrier concentration and mobility came out to be 6.19 × 1015 cm−3 and 31.48 cm2 V−1 s−1 calculated from hall effect measurement. The photosensitive properties of SnS0.25Se0.75 crystal-based photodetector were also investigated under different biasing conditions. The device exhibited an excellent response time of 0.6 s along with good photocurrent and responsivity as compared with previous reports. Additionally, air stability after 1 month under 0 V and 1 mV biasing have been reported. This study assigned that Se doping played a major role in enhancing optoelectronic properties and the composition can be used in potential optoelectronic devices for future applications.

Wavelength dependent anisotropic photosensing activity of zirconium trisulfide crystal

According to the performance requirements, either bulk or nanocrystalline form of the material can be used for different types of device applications. In the present study, zirconium triselenide bulk crystals were grown by direct vapour transport technique. The energy-dispersive X-ray analysis (EDAX) confirms the purity of the grown crystals. The as-grown crystals and powder have been examined under Carl Zeiss optical microscope and scanning electron microscope (SEM) for morphological studies which revealed the evolution of crystalline phases of the material by the layered kind of growth mechanism. The transmission electron microscopy (TEM) with selected area electron diffraction (SAED) pattern analysis showed the grown crystals possess good crystallinity, whereas X-ray diffraction (XRD) analysis confirmed the monoclinic phase of the crystals. To study the effect of different wavelength sources (Blue-470 nm, Green-540 nm, Red-670 nm) on bulk zirconium trisulfide photodetectors, a pulse photo response experiment was carried out. The anisotropic behaviour is also revealed using the same sources. Various device parameters like responsivity, sensitivity, detectivity and external quantum efficiency (EQE%) were calculated. The highest responsivity and detectivity of 81.7 µA/W and 3.56 × 107 Jones were achieved for blue (470 nm) light source, respectively.

Temperature-dependent vibrational properties of DVT grown orthorhombic SnS single crystals and their application as a self-powered photodetector

Metal chalcogenides have gained global consideration in current decades due to their optoelectronic behaviour, excellent optical absorption and tunable bandgap energies. Specifically, SnS (tin sulfide) crystals have attracted significant attention primarily due to their potential applications in photovoltaic devices, photodetectors, field-effect transistors and holographic recording devices. In this work, we have synthesized SnS (tin sulfide) single crystals using a direct vapour transport technique. The layered type growth mechanism has been observed by a scanning electron microscope (SEM). The X-ray diffractogram pattern reveals the orthorhombic structure and phase purity of grown SnS. The Hall effect measurement confirms the p-type nature of grown SnS crystals and the physical parameters such as carrier concentration, conductivity, mobility and hall coefficient were calculated. Raman measurement at a low temperature ranging from 25 °C to −195 °C was performed, and shifting of vibrational modes have been observed. The parameters, such as the first-order temperature coefficient and peak position at 0 K, are evaluated. The photosensitive property at zero biasing voltage observed under the illumination of 395 nm laser and 670 nm laser. Our results demonstrate that SnS single crystals have great potential for application in photodetection devices.

Thermal decomposition study of SnSe single crystals

Single crystals of SnSe are grown by direct vapor transport technique. The elemental composition of as-grown crystals determined by dispersive X-ray energy analysis showed the crystals to be slightly selenium rich and tin deficient. The X-ray powder diffraction showed the crystal to possess orthorhombic unit cell structure. The lattice parameters are in good match with reported data. The surface micro-topography showed flat surfaces with layer edges, stating crystal growth to happen by mechanism of layer growth. The thermo-curves of the as-grown single crystals are recorded in temperature range of 308 K and 1053 K in inert nitrogen atmosphere. The curves are recorded for three thermal heating rates of 10, 15 and 20 K/min. The recorded thermogravimetric curves showed single-step decomposition. The single peak in differential thermogravimetric analysis further confirmed single-step decomposition. The differential thermal analysis of the samples showed initial exothermic followed by endothermic and at last exothermic nature. The thermodynamic variables determined from the thermo-curves data employing Kissinger relation stated absorption of heat leading to non-spontaneous decomposition.

Investigation of anisotropic photoresponse in Re0.2Sn0.8Se2 ternary alloy at low temperature conditions

Photodetectors which can operate at low temperature with multiple configurations are building blocks for the future technology in the field of Photonics. In this work, we have investigated the low temperature anisotropic photoresponse of Re0.2Sn0.8Se2 ternary alloy grown by direct vapor transport (DVT) technique. The time-dependent photoresponse of the Re0.2Sn0.8Se2 ternary alloy is recorded at different temperatures ranging from 300 to 60 K. At 300 K, Re0.2Sn0.8Se2 ternary alloy shows excellent photoresponse in both parallel and perpendicular configurations. We have observed that the Re0.2Sn0.8Se2 ternary alloy retains its outstanding photoresponse ability even at a low temperature of 60 K, in both the parallel and perpendicular configurations. Moreover, the critical parameters related to photodetection properties such as photoresponsivity (Rλ), spectral detectivity (D*), and rise time are evaluated. Our work demonstrates the potential of Re-doped SnSe2 ternary alloys for optoelectronic devices function at low temperatures.

Investigation of optical, electrical and optoelectronic properties of SnSe crystals

The optical, electrical and optoelectronic properties of tin selenide crystals are of immense significance for application in photodetectors and energy conversion and storage devices. The transition metal chalcogenides possess a layered structure that interacts with each other through van der Waal forces and can also offer sites for intercalation. The low molecular weight materials like GeSe and SnSe are found in an orthorhombic structure. In this article, the optical, electrical and optoelectronic properties of as-grown tin selenide crystals are investigated. The chemical composition of the crystals grown with the aid of direct vapour transport (DVT) technique is confirmed through energy Dispersive analysis of X-rays (EDAX), at the same time the morphological analysis is accomplished using optical microscopy and Scanning Electron Microscopy (SEM). The grown crystals are characterized by powder X-ray diffraction (XRD) method to assess the structural properties of the material. The XRD evaluation found out the orthorhombic structure of the crystals with the space group 2h16D (Pcmn) having lattice parameters a = 11.490 A, b = 4.440 A and c = 4.135 A. The crystallinity of grown samples was verified by transmission electron microscopy (TEM). The single crystalline nature of grown crystals was revealed by SAED pattern. The indirect optical band gap of 1.0065 eV, Urbach energy and steepness parameter are calculated utilising UV–VIS-NIR spectrophotometer. The optical absorption of as-grown SnSe crystals has been measured close to the fundamental absorption edge at room temperature. Both types of transitions, i.e. direct and indirect, are involved in the absorption process. Electrical transport properties like resistivity measurements (parallel and perpendicular path to the c-axis) had been carried out on these crystals within the temperature range 297–673 K. Anisotropy in resistivity measurements in both the directions, i.e. parallel and perpendicular direction to the c-axis was discovered. The p-type semiconducting nature was confirmed with the aid of Hall-effect measurements. For the photodetection properties of SnSe crystals, light source (670 nm) having an intensity of 3 mW/cm2 at distinctive biasing voltages is used. The outstanding detection properties are revealed from the responsivity, specific detectivity and external quantum efficiency (EQE) of pure SnSe crystals.

Study of ac and dc electrical resistivity variation with high pressure of as-grown pure, indium and antimony doped SnS single crystals

The direct vapour transport technique grown single crystals of pure SnS, indium (5 and 15 at%) doped SnS and antimony (5 and 15 at%) doped SnS are used in the present study. The as-grown single crystals are completely characterized. The single crystal growth and comprehensive characterization results are presented in another research paper of the authors. All the as-grown single crystals are p-type semiconductors. The ac and dc electrical resistivity variation with high pressure of the as-grown single crystals up to 5 GPa are measured. The obtained ac and dc electrical resistivity variation with high pressure results are deliberated in this paper.

Pure SnSe, In and Sb doped SnSe single crystals – Growth, structural, surface morphology and optical bandgap study

The pure SnSe is a potential material for technological applications due to its favourable electrical, optical, thermal, etc. properties. To make SnSe more suitable for varied applications needs tailoring of properties. In this work, an effort has been made to modify the properties of SnSe by doping with group III (indium) and V (antimony) elements of the periodic table. The pure SnSe, indium (In) and antimony (Sb) doped SnSe single crystals are grown by direct vapour transport technique. Two concentrations of 5% and 10% are employed for doping. The chemical compositions of the grown crystals are confirmed by X-ray energy dispersive and electron probe micro analysis techniques. The X-ray diffraction analysis substantiated the orthorhombic SnSe phase of all grown single crystals. The surface morphology study of the as-grown single crystal surfaces showed the crystal growth to have occurred by layer growth mechanism. The hot point probe technique analysis showed all crystals to be p-type semiconducting in nature. The optical absorption spectra of all as-grown samples showed sharp absorption near 846 nm wavelength. The modification of the optical bandgaps by incorporation of In3+ and Sb3+ ions within SnSe is studied. The obtained results are discussed in details.

Growth and application of WSe2 single crystal synthesized by DVT in thin film hetero-junction photodetector

Tungsten di-selenide (WSe2) belonging to the family of layered transition metal di-chalcogenides (TMDCs) is at present widely used in optoelectronic devices due to their adequate energy band gap suitable for photosensing applications. In the present investigation, WSe2 single crystals are grown by direct vapor transport (DVT) technique in a dual zone horizontal furnace maintaining a temperature difference of 50 K between source zone (SZ) and growth zone (GZ). The crystals thus obtained were thin, shiny and with an average thickness of 30 mm. The surface topography of crystals studied by optical microscope revealed hexagonal spirals on the crystal surface which seemed to arise due to screw dislocation defect. The structural properties of the as grown crystals studied by powder X-ray diffraction (XRD) elucidated good crystallinity, hexagonal structure and confirmed the orientation of crystals along crystallographic c-axis. P-type semiconductor nature of the crystals was affirmed by thermoelectric power (TEP) measurement. Optical and vibrational properties of the grown crystals were studied by UV–Visible, photoluminescence (PL) and Raman spectroscopy. An optical direct band gap of 1.41 eV was determined for the crystals which were micromechanically exfoliated upto few layers. The excitonic mechanism of the grown WSe2 crystal was explained by PL spectroscopy. The results of Raman spectroscopy disclosed A1g and E2g vibrational modes present in the crystals. The current–voltage characteristics of nSnSe/pWSe2 hetero-structure studied using Keithley 2400 SMU showed rectification behavior at low bias voltage in dark and illuminated conditions. The diode parameters like ideality factor and barrier potential were determined to be 2.54 and 0.4 eV, respectively, by following conventional lnI–V method. The photodetection properties of the fabricated device were studied using a Laser source (670 nm) having an intensity of 3 mWcm−2at different bias voltage ranging from 0.3 V to 3 V. Parameters such as responsivity, detectivity and external quantum efficiency (EQE) were calculated to substantiate the excellent detection properties shown by the prepared photodetector using time resolved pulsed photoresponse. Value of responsivity and EQE increased from 42.22 mA W−1 to 533.77 mA W−1 and 7% to 95%, respectively, with increase in bias voltage from 0.3 V to 3 V. Also, detectivity values were found to be of the order of 107 Jones.

Effect of sulphur doping in SnSe single crystals on thermoelectric power

Single crystals of sulfur doped SnSe with the proportion of SnSe0.65S0.35 are grown by direct vapour transport technique. The energy dispersive analysis of x-ray and x-ray diffraction analysis showed the crystals to be stoichiometric and possess orthorhombic unit cell structure, respectively. The surface morphology study of single crystals by scanning electron microscopy showed the growth to have occurred by layer growth mechanism. The optical analysis showed the crystals possess direct and indirect optical bandgaps. The bandgap values are larger than the bandgap values of pure SnSe single crystal. The study of electrical transport properties showed inadequate thermoelectric performance in case of sulphur doped SnSe compared to pure SnSe. The obtained results are discussed in detail.

Tunable and anisotropic photoresponse of layered Re0.2Sn0.8Se2 ternary alloy

In order to produce high-performance optoelectronic devices, alloy engineering has been exploited in ternary transition metal dichalcogenides. In the present study, we demonstrated the effect of rhenium incorporation on the structural and electrical response in SnSe2 layered crystals grown by direct vapour transport technique. Elemental conformation was characterized by EDAX. The powder X-ray diffraction shows the hexagonal phase and high crystallinity of grown compounds, which is also confirmed by the TEM SAED pattern. Perfectly hexagonal shaped microcrystals are shown in SEM surface micrograph. Raman spectra indicate the redshift in the vibrational mode peaks of SnSe2 with the rhenium doping. Current-time characteristic was measured to study to the effect of alloy engineering on the photoresponse ability of the grown compound. Among all, Re0.2Sn0.8Se2 ternary alloy shows the enhanced photoresponse under polychromatic illumination, showing the suppression of deep-level defect states after incorporation of Re in SnSe2 lattice structure. These materials have a layered structure and exhibit the anisotropic conductivity. Hence the anisotropic photodetection characteristics of Re0.2Sn0.8Se2 ternary alloy based photodetectors are further studied in detail. Photocurrent and photo responsivity are higher along the symmetric contacts, whereas along the asymmetric contacts both the quantities are lower in magnitude because the photogenerated carriers have to cross the perpendicular resistance of is layers stacked together by the weak Vander Waal's forces. Increasing the bias voltage enhances the photoresponsivity from 5.141 mAW−1 to 67.231 mAW−1 and photodetectivity 0.971 to 3.452 × 109 Jones. Anisotropic photoresponse was also studied under the monochromatic light. Results provide the significant understanding of tunable and layered structure dependent anisotropic photoresponse ability of TMDC materials.

Growth and application of Sb0.5Mo0.5Se2 ternary alloy as photodetector

Presently, ternary alloy engineering holds ability in promoting high performance photo detecting devices. In the present investigation, we have employed direct vapor transport technique (DVT) to grow Sb0.5Mo0.5Se2 multilayer crystal for its use as photodetector. To confirm the composition of the grown crystals, energy dispersive analysis of x-ray (EDAX) is performed. To explore the morphological properties, optical microscopy and scanning electron microscopy (SEM) are used and the growth from vapor phase that is initiated due to screw dislocation is observed. The phase composition and optical properties of the as grown crystals are examined by transmission electron microscopy (TEM) and UV–Visible spectroscopy providing indirect energy band gap of 1.22 eV. Raman spectra of both pure MoSe2 and Sb0.5Mo0.5Se2 show the presence of the out of plane A1g vibrational mode at 243 cm−1. In addition, to study photo conduction property, the mechanically exfoliated crystal was illuminated by polychromatic source having intensity of 50 mWcm−2 at different bias voltages.

Transient photoresponse of infrared photodetector based on Sb0.1Sn0.9Se2 ternary alloy

In this article, we demonstrated the growth and optoelectronic application of Sb0.1Sn0.9Se2 ternary alloy. The single crystals of Sb0.1Sn0.9Se2 ternary alloy are grown by direct vapour transport technique. The grown compound has 2H–SnSe2 type hexagonal lattice structure in which Sb+5 is well substituted on Sn+4 lattice sites. Subsequently, the photodetector is fabricated and explored under IR illumination (1088 nm) of different power intensity ranging from 1 to 80 mW cm−2 at room temperature (300 K). The detector shows excellent response with enhanced photoresponsivity of 84.22 mW A−1 and specific detectivity of 2.53 × 109 Jones. The temperature dependent photoresponse of photodetector in investigated in temperature range 210 to 300 K. The detector showed stable response in studied temperature range. The present finding on photodetector suggest the novel ternary composition for application as infrared photodetection.

Effect of off-stoichiometry on properties of tin selenide crystals

The tin selenide crystals with different proportions of Sn and Se were grown by a direct vapour-transport technique. The layer by layer growth of crystals from the vapour phase was promoted by screw dislocation mechanism. The powder X-ray diffraction (XRD) shows good crystallinity of grown compound. The XRD patterns of grown compounds are well-indexed to orthorhombic structure. In the off-stoichiometric compound, evidence of $$\hbox {SnSe}_{{2}}$$ secondary phase is observed due to excess of selenium. The morphological investigations were carried out using a Carl Zeiss optical microscope. The electron diffraction was also recorded from tiny flakes using a transmission electron microscope. The electrical resistivity both parallel and perpendicular to the c-axis was measured in the temperature range of 303–490 K and activation energy was also calculated using Arrhenius relation. The electrical study depicts the extrinsic semiconducting nature of grown compositions.

Structural and electrical properties of SbxW1−xSe2 (0, 0.5) ternary alloys

In present article, we demonstrated for the first time the synthesis and properties of SbXW1−xSe2 (0, 0.5) ternary alloys. The crystals of SbXW1−xSe2 (0, 0.5) ternary alloys were grown by direct vapour transport technique. The XRD results confirm the 2H-hexagonal lattice structure with P63/mmc space group and grown crystals are highly crystallographic c-axis oriented. The screw dislocation mechanism is predominating in the growth process of Sb0.5W0.5Se2 crystals. The results of electrical characterization show n-type semiconducting nature. The Raman spectra exhibit peaks corresponding to out of plane A1g, in-plane E2g and 2LA modes of vibration which is attributing the 2H-polymorph of grown SbXW1−xSe2 (0, 0.5) ternary alloys. The results shows substitution of Sb (+5) on W (+4) lattice site due to similar ionic size. The band gap tailoring from 0.93 to 1.40 eV is achieved, suggesting the effective way to tune the material characteristics for high performance devices.

Effect of indium and antimony doping on the transport properties of direct vapour transport (DVT) grown SnSe single crystals

Pure SnSe, 5% In, 10% In, 5% Sb, and 10% Sb doped SnSe single crystals were grown by the direct vapour transport technique. The energy dispersive X-ray analysis study of the samples showed them to be near stoichiometric but slightly Sn deficient. The X-ray diffraction study of all the as-grown single crystal samples showed that they possess an orthorhombic structure and the lattice parameters are in good agreement with the reported parameters. The thermoelectric power (S), dc electrical conductivity (σ), and thermal conductivity (κ) variation with temperature from ambient to 573 K substantiated the semiconducting nature of all the five samples. The sign of “S” was positive for all five samples for all the temperature range stating the sample to be a p-type semiconductor. The power factor (S2σ) and figure of merit (ZT) variation with temperature showed that pure SnSe possesses the highest value compared to doped samples. The obtained results are studied and discussed in detail.

Study of indium and antimony incorporation into SnS2 single crystals

Pure SnS2, 5% In-doped SnS2, 15% In-doped SnS2, 5% Sb-doped SnS2 and 15% Sb-doped SnS2 single crystals are grown in closed sealed quartz ampoule by direct vapour transport technique. The energy dispersive analysis of X-rays analysis of all the five as-grown single crystals showed them to be stoichiometric. The X-ray diffraction analysis showed that all the crystals are single phase possessing a hexagonal structure with (0 0 1) preferential orientation. The surface morphology of as-grown single crystals studied by scanning electron microscopy and optical microscopy showed crystal growth is by layer growth mechanism supported by screw dislocation. Selected area electron diffraction showed hexagonal spot pattern confirming the single crystalline nature of the crystals. Optical bandgap of the as-grown crystals determined by UV–Vis-NIR spectroscopy showed that the single crystals possess direct optical bandgap and the value varied between 1.89 and 2.31 eV. The photoluminescence spectra study showed the presence of six peaks. The Raman spectra showed SnS2 type the A1g vibrational mode and shifting in A1g vibrational mode with In and Sb doping. The results are elaborated in details.

Alloy engineering to promote photodetection in InxSn1−xS2 and SbxSn1−xS2 ternary alloys

To produce high performance optoelectronic devices, ternary alloys prepared by indium (In), antimony (Sb), tin (Sn) and sulphur (S), the InxSn1−xS2 and SbxSn1−xS2 (x = 0, 0.05, 0.15), are exploited for their application in moderately fast photodetection. The single crystals of InxSn1−xS2 and SbxSn1−xS2 (x = 0, 0.05, 0.15) alloys are grown by direct vapour transport technique. The photodetectors based on single crystals are examined for 670 nm illumination having power intensity of 3 mW/cm2. For quantitative analysis, the typical detector parameters such as photo-responsivity, specific detectivity and external quantum efficiency are calculated. The improvement in photodetection with significantly enhanced detector parameters and fast a response is realized due to doping in SnS2. The highest responsivity of 15.48 mA/W with response time of 240 ms is achieved in Sb0.15Sn0.85S2 alloy. The present findings of enhanced photodetection due to alloy engineering can be of great advantage in intended applications of these compounds in the field of optoelectronics.

Influence of alloy engineering on structural and photo detection properties of SbXSn1-XSe2 ternary alloys

In order to exploit effect of Sb incorporation on properties of SnSe2, alloy engineering is performed in SbxSn1-xSe2 (x = 0, 0.1, 0.2, 0.3) ternary compounds. The single crystals are grown by direct vapour transport technique. The elemental composition and purity of as-grown compounds are characterized by EDAX. The optical microscopy and scanning electron microscopy show characteristic morphological features like helical spiral, layered structure, clean surface, etc. on surface of grown crystals. The powder X-ray diffraction shows that the pristine and Sb incorporated samples possess 2H-Hexahonal lattice structure. However, lattice parameters and unitcell volume are changed on incorporation of Sb in SnSe2 structure due to increase in microstrain. The Raman spectroscopy reveals SnSe2-type A1g vibrational mode and the corresponding peak is shifted on lower wavenumber side on increasing Sb content. The results confirm substitution of Sb(+5) on Sn(+4) lattice site in host network. The influence of alloy engineering on photo response is studied. The highest photocurrent of 1.88 μA, responsivity of 43.45 mAW−1, detectivity of 18.25 × 1011 Jones and EQE (%) of 47.28% are observed for X = 0.1 sample.