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The successful application of nanotechnologies in enhancing thermoelectric properties of n-type Bi2Te3 alloys remains a formidable challenge, despite significant advancements in their p-type counterparts. The distinctive challenges inherent to n-type materials include the complex relationships between defect structures and electron concentration, and the strong anisotropy of thermoelectric properties. Electrons originate from various defect structures, such as impurity dopants, vacancies, antisite defects, and grain/domain boundaries, which sensitively varies depending on material synthesis processes. Moreover, the pronounced anisotropic nature of thermoelectric properties requires grain alignment along specific crystallographic directions. Therefore, the challenges in achieving high-performance n-type Bi2Te3 alloys lie in the difficulties of independently controlling defect structures (electron concentration), textured microstructures (electron/phonon transport property), and nanofeatures. This review aims to provide a comprehensive understanding of the difficulties and challenges associated with these aspects, and to discuss potential routes for realizing high-performance n-type Bi2Te3 alloys. [ABSTRACT FROM AUTHOR]

We have investigated the growth of BiSbTe3 films by metal organic vapor phase epitaxy on (001) GaAs vicinal substrates. A detailed experimental study of the surface morphologies of BiSbTe3 films grown on GaAs (001) vicinal surfaces was carried out and is discussed in this paper with a view to understanding the step-step interaction kinetics that result in step bunching. BiSbTe3 layers grown on nominal (001) GaAs substrates exhibit triangular facet structures consisting of atomically flat plateau areas separated by steps. In contrast, the growth of films on vicinal substrates was found to result in regular arrays of terrace step structures. The formation of step bunches and rectangular terraces on such film surface is attributed to the preferential incorporation of adatoms at step or kink sites and lateral growth rate anisotropy. [ABSTRACT FROM AUTHOR]

We have investigated the structural properties of ZnSe epilayers that were molecular beam epitaxially grown on (001) GaAs substrates with different tilt angles and tilt directions. We measured the properties of the epilayers by x-ray diffraction, transmission electron microscopy, and etch pit density analysis. Tilting the (001) GaAs substrate toward [010] was very effective in reducing the surface defect density of the ZnSe layers, while tilting toward the [110] direction was of no use. We could observe the increasingly two-dimensional nature of the initial growth mode in the (001) GaAs substrate tilted toward [010]. Growth of a 1.8-μm-thick ZnSe layer on (001) GaAs tilted 4° toward [010] resulted in a very low surface defect density of 1×10[sub 4] cm[sup -2]. Such a low defect density has seldom been obtained in ZnSe, without growing a GaAs buffer layer below the ZnSe layer. [ABSTRACT FROM AUTHOR]

We performed capacitance-voltage analysis of 5-nm-thick LaAlO3/SrTiO3 heterostructure containing two-dimensional-electron-gas (2DEG) at the interface. The complex impedance of the heterostructure was measured as a function of frequency for a wide range of gate biases. The impedance spectra showed a different behavior above and below an applied voltage of -1.8 V. The capacitance determined from the impedance was approximately 1.2 nF above -1.8 V and was drastically reduced to ∼0.01 nF below this voltage, owing to depletion of 2DEG and the insulating SrTiO3 underneath it. This suggests that devices utilizing LaAlO3/SrTiO3 can facilitate switching operations in a very small voltage range. [ABSTRACT FROM AUTHOR]

The two-dimensional electron gas formed at LaAlO3/SrTiO3 heterointerfaces exhibits a variety of interesting physical properties. Herein, we report on tunable conductivity at LaAlO3/SrxCa1-xTiO3 heterostructures. By changing the Sr content in the SrxCa1-xTiO3 (0 ≤ x ≤ 1) layers, the orthorhombicity of the films, which inevitably accompanies TiO6 octahedral distortions in the unit cells, could be varied. As a result, the interfacial conductivity can be tuned over 6 orders of magnitude. We suggest that the use of pseudosubstrates with chemical substitution or alloying is a promising route to finely tune conductivity at oxide heterointerfaces. [ABSTRACT FROM AUTHOR]

Harman method is a rapid and simple technique to measure thermoelectric properties. However, its validity has been often questioned due to the over-simplified assumptions that this method relies on. Here, we quantitatively investigate the influence of the previously ignored parasitic thermal effects on the Harman method and develop a method to determine an intrinsic ZT. We expand the original Harman relation with three extra terms: heat losses via both the lead wires and radiation, and Joule heating within the sample. Based on the expanded Harman relation, we use differential measurement of the sample geometry to measure the intrinsic ZT. To separately evaluate the parasitic terms, the measured ZTs with systematically varied sample geometries and the lead wire types are fitted to the expanded relation. A huge discrepancy (∼28%) of the measured ZTs depending on the measurement configuration is observed. We are able to separately evaluate those parasitic terms. This work will help to evaluate the intrinsic thermoelectric property with Harman method by eliminating ambiguities coming from extrinsic effects.