Electrical properties of polycrystalline Sb2Te3 films

Single-phase polycrystalline stoichiometric films of Sb₂Te₃ with different thicknesses were prepared on glass substrates by a flash evaporation technique at constant substrate temperature of 423 K. The electrical properties of these films, such as resistivity, Hall mobility, carrier concentration and activation energy, were determined for different film thicknesses. The optical absorption of these films was also studied. The implications are discussed.     

Electrical and optical properties of Indium sesquitelluride (In2Te3) thin films

Indium sesquitelluride (In₂Te₃) thin films were grown on glass substrates using a flash evaporation technique. The nature of contact phenomena of Ag, Sn, In, Zn, Al-(p) In₂Te₃ junctions had been investigated. Ag, Sn, In and Zn metals were found to provide ohmic contact for In₂Te₃ thin films. The variation of DC-electrical resistivity of In₂Te₃ thin films with temperature was studied at different substrate temperatures. The optical measurements revealed that the flash evaporated In₂Te₃ thin films possessing direct energy band-gap. The variation of optical energy gap with substrate temperature was investigated. Film thickness, substrate temperature, composition and crystallinity were found to determine the optimization of electrical and optical properties of In₂Te₃ thin film.     

Temperature induced electrical transport in n-Bi2Te3/p-InAs thermoelectric heterojunctions

Journal of Materials Science - Thermoelectric semiconductor devices have recently attracted more interest since their electrical properties can be further adjusted by the temperature field. Many...     

Aqueous precipitation and electrical properties of In2S3: characterization of the In2S3/polyaniline and In2S3/polypyrrole heterojunctions

The stability of indium sulphide aqueous supersaturated solutions at pH 2.50 and 25°C was investigated. Spontaneous precipitation proceeded at rates proportional to the solution supersaturation via a polynuclear mechanism and the phase formed was identified as In₂S₃. The absorption spectrum of In₂S₃ was measured from 190–800 nm and from the absorption threshold the optical energy gap was estimated to be E ₀ = (1.8 ± 0.1) eV. The thermal energy gap E _t = (1.6 ± 0.2)eV was determined from resistivity against temperature measurements and a thermopower coefficient S = –100VK^–1 at room temperature was found. Finally, In₂S₃/polyaniline and In₂S₃/polypyrrole heterojunctions were prepared and from the investigation of their I–V characteristics, the values of the ideality factor, n, the saturation current density, J ₀, and the effective barrier height, _B, were determined to be n = (15 ± 2), J ₀ = (38 ± 7) A m^–2 and _B = 0.56 eV for the polyaniline and n = (64 ± 8), J ₀ = (13 ± 2) A m^–2 and _B = 0.59 eV for the polypyrrole heterojunction.     

In Situ TEM Investigations on Thermoelectric Bi2Te3/Sb2Te3 Multilayers

In this work, the impact of heat treatment on the real structure of Bi₂Te₃/Sb₂Te₃ multilayers is investigated. The material was heated in situ in the transmission electron microscope (TEM) and ex situ inside a furnace after preparing these layers with the so‐called nanoalloying deposition technique via molecular beam epitaxy (MBE) equipment. The samples were prepared as a lamella for TEM studies using focused ion beam technique. EDX elemental mapping and high angle annular dark field mode‐STEM were performed to monitor changes of the morphology and interdiffusion phenomena after heating up to 250 °C. A grain growth started during heating and the chemical layer structure was smeared out partly but remained in several grains and was found to be adjusted parallel to a major lattice plane in a crystallite. High resolution TEM shows polysynthetic twinning in a number of crystals.     

大直径Hg_3In_2Te_6晶体生长与性能表征

采用垂直布里奇曼法,成功生长出大直径Hg3In2Te6(Φ=30mm)晶体。通过傅立叶红外透射光谱测试了晶锭不同部位的红外透过率,并利用X射线双晶摇摆曲线表征了晶体的结晶质量。结果表明,定向切割晶片为(111)面单晶,衍射峰位于θ=12.1665°处,半峰宽为0.0760°;中部单晶片红外透过率平均值为50%,接近Hg3In2Te6晶体的红外透过率最大值57%。位错和成分非均匀性是造成晶锭不同部位红外透过率差异的主要因素。     

Growth and electrical transport properties of In2Te3 thin films

Hall coefficient and d.c. conductivity studies in the temperature range 100–625 K were made on polycrystalline In₂Te₃ films grown on glass and mica substrates. When the films were cycled above about 525 K the conductivity was found to be irreversible; this is explained in terms of structural changes at high temperature. It was found that the Hall mobilities of the films are independent of temperature, showing the predominance of neutral impurity scattering over again boundary scattering.     

Electrical and photovoltaic properties of tin oxide-silicon heterojunctions

SnO₂-Si heterojunctions, using n-type and p-type single crystals of silicon, were fabricated by depositing tin oxide using a chemical vapour deposition technique. The electrical and photovoltaic characteristics of these heterojunctions were investigated. The polarity observed in V_oc and I_sc is consistent with the band bending of a simple SnO₂Si heterojunction energy band diagram, neglecting interface states. The results also show that the (n?n) SnO₂Si heterojunction has better electrical and photovoltaic characteristics than the (n?p) SnO₂Si heterojunction. Typical values of V_oc and J_sc (under Air Mass 1 conditions) for an (n?n) SnO₂Si heterojunction are 0.485 V and 16.0 mA cm^-2 respectively, resulting in an efficiency of nearly 5%.     

The effect of fast annealing treatment on the interface structure and electrical properties of Au/Hg3In2Te6 contact

The effect of fast annealing treatment on the electrical properties and interface structures of Au/Hg₃In₂Te₆ contact has been studied by means of current–voltage test and high-resolution transmission electron microscopy. The current–voltage characteristics of Au/Hg₃In₂Te₆ indicate an improvement of the Schottky barrier height (SBH) from 0.557 to 0.601 eV after proper annealing treatment. Meanwhile, the orthorhombic AuTe₂ particles with irregular morphology formed near the interface region after 200 °C annealing treatment. These particles were generated by chemical reaction between Au and Te atoms rather than the phase transformation process. Two types of crystallographic orientation relationship were confirmed between AuTe₂ particles and the Hg₃In₂Te₆ matrix owing to the orientation attachment mechanism. Based on the results, it is believed that the formation of the AuTe₂ phase is likely to introduce additional energy level in Hg₃In₂Te₆, leading to the upward of band bending and increment of SBH.     

Electrical and optical properties of In2Se3 thin films

In₂Se₃ thin films were grown with good stoichiometry at a substrate temperature around 460 K in the α phase and were shown to remain in the β phase above 480 K. The Hall coefficient and the d.c. conductivity of polycrystalline In₂Se₃ films grown on Pyrex and mica substrates were studied in the temperature range 77–530 K. After thermal treatment above 473 K of the α phase thin film, the electrical resistivity decreased and the sample remained in an irreversible phase. This is explained in terms of structural changes at high temperatures. The mobility behaviour of the β phase annealed thin films is illustrated. We use the Petritz barrier model to explain the activation energy of the mobility as due to the grain boundaries of the polycrystallites.The optical properties (refractive index and absorption coefficient) are also reported. The direct band gaps of In₂Se₃ thin films are 1.43 eV and 1.55 eV for the α phase and β phase respectively. These values are obtained from transmission measurements and are confirmed through photoconductivity measurements.     

Effect of annealing on the structural and electrical properties of In2Te3

Amorphous In2Te3 was prepared in both bulk form, by quenching the molten material, and thin-film form, by the thermal evaporation technique. X-ray diffraction analysis showed that the prepared samples in bulk and as-deposited thin-film forms were in the amorphous state. - and -phases of In2Te3 were prepared by annealing bulk samples at 615 and 813 K, respectively. Films annealed at 573 K give -phase polycrystalline structure. The electrical conductivity for the as-deposited In2Te3 films increases with increasing film thickness. The conduction activation energy, E, of the as-prepared bulk and thin film samples were found to be 0.516 and 0.521 eV. The corresponding values of room-temperature electrical conductivity, RT, for these samples are 1.1×10-6 and 7.15×10-7-1m-1, respectively. The observed change in the value of RT may be due to the difference in the structure of bulk and thin-film samples. The increase of E with annealing temperature for both bulk and thin-film samples is interpreted in terms of the density of states model proposed by Mott and Davis. © 1998 Chapman & Hall     

Study of the strain-resistance properties of massive samples of Bi2Te3-Sb2Te3 and Bi2Te3-Bi2Se3

The coefficients of strain sensitivity of polycrystalline samples of ternary alloys based on bismuth and antimony chalcogenides were measured and the strain sensitivity of Peltier thermocouples of low height under real working conditions were evaluated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 56, No. 1, pp. 97–99, January, 1989.     

Electrical and optical properties of (Sb2Se3)2 (Sb2Te3)1 thin films

A study of the synthesized (Sb₂Se₃)₂ (Sb₂Te₃)₁ glassy system has been carried out, X-ray diffraction (XRD) patterns and differential thermal analysis (DTA) of the system studied were used to obtain an insight into the structural information. An investigation of the electrical and optical properties of (Sb₂Se₃)₂ (Sb₂Te₃)₁ thin films prepared by thermal evaporation having different thicknesses (89.2, 214, 223 nm) and annealing temperatures ranging from 300 to 473 K has been carried out. The effect of the thickness and heat treatment on the activation energy E for d.c. conductivity and the density of localized states at the Fermi level N(E_F) were carried out. The electrical conductivity measurements depend on the thickness and annealing temperature, and exhibit two types of conduction mechanisms. Optical absorption measurements have been made on as-deposited and annealed films for the investigated system. The optical transition was found to be indirect. The optical energy gap (E_opt) decreases with increasing thickness and annealing temperatures (below T_g). The corresponding band is approximately twice the conduction activation energy. This effect is interpreted in terms of the density of states model proposed by Mott and Davis. © 2002 Kluwer Academic Publisher     

Bi_2Te_3/炭黑复合材料的制备及热电性能

采用水热法合成Bi_2Te_3粉体,将炭黑(CB)与其掺杂制备不同比例的碲化铋/炭黑(Bi_2Te_3/CB)复合材料,研究复合材料的热电性能。同时采用TGA、SEM、XRD等分析方法表征Bi_2Te_3/CB复合材料的结构,探究微观结构与热电性能的关系。研究发现:室温下,CB的引入使Bi_2Te_3/CB复合材料的热导率大大降低(0.5957 W/(m·K)降到0.0888 W/(m·K));随着Bi_2Te_3含量的增加,复合材料的电导率、热导率均增大,Seebeck系数先增加后降低;当Bi_2Te_3含量为88.9%时,在558℃烧结10min所得的Bi_2Te_3/CB复合材料室温下热电优值ZT最大(ZT=0.21)。虽然ZT值未能达到应用价值,但是CB的添加为改善Bi_2Te_3材料的热电性能,尤其在降低材料的热导率方面,提供了新方法和新思路。     

Electrical properties of Na1/2Nd1/2TiO3 Ceramics

The polycrystalline sample of Na_1/2Nd_1/2TiO₃ was prepared by a high-temperature solid-state reaction technique. The formation of the compound was confirmed by both XRD and EDX studies. Preliminary structural analysis ofNa_1/2Nd_1/2TiO₃ using X-ray diffraction data exhibits a tetragonal phase of the material at room temperature. The dielectric permittivity and the loss tangent of the pellet sample were obtained in a wide frequency range (1 kHz to 1 MHz) at different temperatures (30 °C to 425 °C). The dielectric anomaly at 114 °C, appearance of hysteresis loop and piezoelectric properties at room temperature confirmed the ferroelectric properties of the compound. Measurements of frequency and temperature dependence of impedance over a wide frequency range (100Hz–1MHz) were carried out by complex impedance spectroscopy as a non-destructive tool and indicate that the electrical properties of the material are strongly temperature dependent. Evidence of temperature dependence of electrical relaxation phenomenon as well as the negative temperature coefficient (NTC)-type of resistance behavior of the sample has also been observed. The dc conductivity graph follows the Arrhenius law. Studies of dielectric modulus suggest the non-Debye type of relaxation in the materials, which is supported by the impedance data.     

Electrical properties of TeAsGe films

The effect of temperature T, electrode separation d and substrate temperature T_s on the I–V characteristics of amorphous films 3500 Å thick, vapour deposited from the alloy TeAsGe (53:36:11 at. %) onto a glass substrate at room temperature, were investigated. The material displayed the behaviour of a negative resistance device with a memory. The behaviour for T=constant is described by the relation V = CIexp (?αI), where C and α are constants for a specimen at constant temperature. The threshold voltage at which the off state transforms to the negative resistance state decreased with T according to the relation V_th = V₀exp (E_v/2 kT), where E_v = 0.21 eV. V_th increased with d and decreased with T_s and was related to changes in resistance and structure. Microscope examination showed the formation of filaments containing recrystalized structure arising from Joule heating.     

碲铟汞(111)晶面腐蚀坑的研究

通过扫描电镜、扫描探针显微镜和电子背散射衍射仪对改进的Chen法腐蚀液在Hg3In2Te6(111)晶片上形成的腐蚀坑进行了研究。实验发现,腐蚀坑形貌主要有线形、梭形、枣形3种,且后两者的沟槽在(111)面的投影只有3种取向,并互成120°夹角。进一步分析的结果表明,上述蚀坑的形成可由螺位错双交滑移的模型加以解释。     

p-GaSe-n-Ga2S3 heterojunctions

Epitaxial layers of n-Ga₂S₃ have been grown on p-GaSe single crystals annealed in sulfur vapor. The possibility of fabricating p-GaSe-n-Ga₂S₃ heterojunctions is demonstrated. Pis’ma Zh. Tekh. Fiz. 23, 22–24 (May 26, 1997)