The influence of gas adsorption and temperature on the electrical resistivity of SnSe thin films

Atmospheric pressure chemical vapour deposition of SnSe and SnSe2 thin films on glass

Abstract: Atmospheric pressure chemical vapour deposition of tin monoselenide and tin diselenide films on glass substrate was achieved by reaction of diethyl selenide with tin tetrachloride at 350–650 °C. X-ray diffraction showed that all the films were crystalline and matched the reported pattern for SnSe and/or SnSe2. Wavelength dispersive analysis by X-rays show a variable Sn:Se ratio from 1:1 to 1:2 depending on conditions. The deposition temperature, flow rates and position on the substrate determined whether mixed SnSe–SnSe2, pure SnSe or pure SnSe2 thin films could be obtained. SnSe films were obtained at 650 °C with a SnCl4 to Et2Se ratio greater than 10. The SnSe films were silver–black in appearance and adhesive. SnSe2 films were obtained at 600–650 °C they had a black appearance and were composed of 10 to 80 μm sized adherent crystals. Films of SnSe only 100 nm thick showed complete absorbtion at 300–1100 nm.

Novel semiconductor materials for the development of chemical sensors and biosensors: a review.

Abstract: The aim of this manuscript is to provide a condensed overview of the contribution of certain relatively new semiconductor substrates in the development of chemical and biochemical field effect transistors. The silicon era is initially reviewed providing the background onto which the deployment of the new semiconductor materials for the development of bio-chem-FETs is based on. Subsequently emphasis is given to the selective interaction of novel semiconductor surfaces, including doped conductive diamond, gallium nitride, and indium nitride, with the analyte, and how this interaction can be properly transduced using semiconductor technology. The main advantages and drawbacks of these materials, as well as their future prospects for their applications in the sensor area are also described.

Perspectives on SnSe-based thin film solar cells: a comprehensive review

Abstract: Currently, selenium (Se)-based compound semiconductors (CISe, CIGSe and CZTSe) are considered as the active materials in the photovoltaic world. However, these materials exhibit couple of issues related to stoichiometry maintenance and scarcity of their constituent elements (In, Ga), which limit their massive production for future energy demands. These issues could be rectified by introducing a non-toxic, inexpensive and earth-abundant binary material. One such material is a tin monoselenide (SnSe), which exhibits a high chemical stability along with attractive physical properties namely, suitable band gap (1.3 eV), high absorption coefficient (105 cm−1) and p-type conductivity. These properties indicate SnSe as a competitive substitute in place of conventional absorbers in thin film solar cells. Despite of its remarkable properties, only a few reports were published on the fabrication of SnSe-based solar cells with poor efficiency (≤1 %). This indicates a need to review on the physical properties of SnSe and its device structures in a deeper sense. In this context, the present review describes the different methods of preparation of SnSe films and their physical properties along with the details of photovoltaic device fabrication. We highlighted the different factors that are limiting the efficiency of SnSe solar cells, and a few suggestions were included to overcome these problems for further improvement of these cells. This review will enrich and stimulate the readers to further investigate the growth of SnSe thin films and their devices, for the development of >20 % efficient SnSe solar cells.

7 – Bio-chem-FETs: field effect transistors for biological sensing

Abstract: : Field effect transistors (FETs) are electrochemical transducers upon which micro-sized solid-state chemical sensors and biosensors, the so-called Bio-chem-FETs, can be developed. The chapter first discusses the key issues of FET operation. It then describes the ways of introducing chemical and biochemical sensitivity and selectivity to analytes, using either chemically activ sensing elements or biological recognition elements. The new advances in Bio-chem-FET design, based on novel carbon and inorganic nanomaterials, are then presented. Finally, the current analytical limitations are presented, followed by a discussion on the future trends and possible improvement strategies of the Bio-chem-FETs in relation to low detection limits, high sensitivity, in-vivo applications and long operational lifetimes.

A quasi-static technique for MOS C-V and surface state measurements

Abstract: A quasi-static technique is discussed for obtaining the ‘low frequency’ thermal equilibrium MOS capacitance-voltage characteristics The method is based on a measurement of the MOS charging current in response to a linear voltage ramp, so that the charging current is directly proportional to the incremental MOS capacitance With this technique, surface potential and the surface state density can be obtained relatively simply and over a large part of the energy gap on a single sample, while also providing a direct test for the presence of gross nonuniformities in MOS structures This method has been used to determine the surface state distribution at the interface of a bias grown steam oxide and 10 ω-cm n -type silicon, and the results are compared with composite measurements using the conductance technique for a similar interface The sensitivity for surface state density measurements is estimated to be of the order of 10 10 states per cm 2 eV near mid-gap for 10 ω-cm silicon and improves with decreasing doping density Some applications and limitations are also briefly discussed

Polymorphism in some iv‐vi compounds induced by high pressure and thin‐film epitaxial growth

Abstract: The NaCl structures PbS, PbSe, PbTe and SnTe have been found to transform to a Pnma orthorhombic (distorted NaCl) structure under high pressures. Epitaxial growth on rock salt of thin films of normally orthorhombic (Pnma) SnS, SnSe and PbSnS2 induces NaCl structures. There exists a close correlation between the lattice constants of the corresponding NaCl and the orthorhombic polymorphic structures of the Pb and Sn compounds.

Charge transfer controlled surface interactions between oxygen and CdSe films

Abstract: The interaction of oxygen with CdSe surfaces has been studied with thin films of CdSe evaporated in ultra high vacuum in the temperature range 0–360°C and pressure range 10−4−10mm Hg. The effect was monitored via conductivity measurements, carried out in situ. When oxygen is introduced, the initially “clean” film undergoes an instantaneous irreversible chemisorption followed by a slow uptake which is also irreversible in the studied temperature range. This interaction brings about a 3–5 orders of magnitude decrease in the conductivity of the n-type film, i.e. oxygen exhibits acceptor-like properties. The rate of the slow irreversible oxygen uptake can be expressed as d N d t = kP 1 4 o 2 exp ( − bN) and the activation energy for the process has been measured. Donor type weakly adsorbed oxygen was also found to be present on CdSe films which could be reversibly removed from the surface; this reaction was also accompanied by charge transfer and was strongly pressure dependent. The heat of reaction for this process is 12 kcal mole . The boundary layer theory was evoked to explain the kinetics of the slow uptake of the acceptor-like oxygen. Attempts have been made to explain the mechanism of the different surface reactions.

SnSe single crystals: Sublimation growth, deviation from stoichiometry and electrical properties

Abstract: Large SnSe single crystals of high metallurgical quality have been grown by a closed tube vapor phase technique. Hall measurements on annealed and quenched samples were performed to establish the stability range of the compound. The crystals are p-type with hole concentrations between 3 × 1015 and 2 × 1018 cm−3 and mobilities up to 7 × 103 cm /Vs at 77 K.