Metal oxides are widely used in many applications such as thermoelectric, solar cells, sensors, transistors, and optoelectronic devices due to their outstanding mechanical, chemical, electrical, and optical properties. For instance, their high Seebeck coefficient, high thermal stability, and earth abundancy make them suitable for thermoelectric power generation, particularly at a high-temperature regime. In this article, we review the recent advances of developing high electrical properties of metal oxides and their applications in thermoelectric, solar cells, sensors, and other optoelectronic devices. The materials examined include both narrow-band-gap (e.g., Na x CoO 2 , Ca 3 Co 4 O 9 , BiCuSeO, CaMnO 3 , SrTiO 3 ) and wide-band-gap materials (e.g., ZnO-based, SnO 2 -based, In 2 O 3 -based). Unlike previous review articles, the focus of this study is on identifying an effective doping mechanism of different metal oxides to reach a high power factor. Effective dopants and doping strategies to achieve high carrier concentration and high electrical conductivities are highlighted in this review to enable the advanced applications of metal oxides in thermoelectric power generation and beyond.

III-Nitrides are attracting considerable attention as promising materials for a wide variety of applications due to their wide coverage of direct bandgap range, high electron mobility, high thermal stability and many other exceptional properties. The light-emitting diodes based on III-Nitrides revolutionize the solid-state lighting industry. III-Nitrides based solar cells and thermoelectric generators support the sustainable energy progress, and the III-Nitrides are better alternatives for power and radio frequency (RF) electronics compared with silicon. The doped III-Nitrides' magnetic properties and sensitivity to radiation can contribute to novel spintronic and nuclear detection devices. This paper will review III-nitride material properties and their corresponding applications in LEDs, solar cells, power and radio frequency (RF) electronics, magnetic devices, thermoelectrics and nuclear detection. The typical values of electrical, optical, thermoelectric, magnetic properties are cited, the current state of art investigations are reported, and the future applications are estimated. The III-Nitrides, typically composed of GaN and its alloys with Al and In, are compound semiconductor materials with superior properties and well developed growth techniques 1 that has enabled their use in a board range of applications. The III-Nitrides have a hexagonal wurtzite structure and a continuous alloy system with tunable direct bandgaps from 6.2 eV (AlN) through 3.4 eV (GaN) to 0.7 eV (InN) 2 ( Figure 1). This wide coverage of direct bandgap range from deepultraviolet (UV) to infrared region promises a variety of applications in optoelectronics, such as light-emitting diodes (LEDs), lasers, photodetectors and solar cells. GaN is recognized with high breakdown field, high thermal conductivity, and high electron mobility, making GaN an excellent candidate for high power and RF electronic devices. III-Nitrides exhibit high Seebeck coefficient and excellent temperature stability for high temperature thermoelectric applications. Doped GaN exhibit other unique properties with associated applications; such as transition and rare-earth metals doped GaN with magnetic properties, and indium (In)/gadolinium (Gd)/boron (B)/and lithium (Li) doped GaN for nuclear detection. The ability to access such a wide spectral region and these numerous applications has traditionally required the use of many different III-V materials and complex device structures before the advent of the III-Nitrides. [3][4][5][6][7][8][9] This paper will review various applications of III-Nitrides in including LEDs, solar cells, power and RF electronics, magnetic properties, thermoelectrics and nuclear detection applications, along with their development history, current state of art and future explorations. The III-Nitrides for Light-Emitting DiodesLight-Emitting Diodes are a type of solid state lighting (SSL) source with compact size, high energy efficiency and long lifetime. High brightness LEDs have various application in traffic lights, automobile brake ligh...

III-nitride InGaN-based solar cells have gained importance because their band gap can potentially cover most of the solar spectrum, spanning 0.7 eV to 3.4 eV. However, to use these materials to harvest additional energy, other properties such as their thermoelectric properties should be exploited. In this work, the Seebeck coefficient and the electrical conductivity of three InGaN alloys with various indium concentrations and Gd-doped GaN (GaN:Gd) were measured, and the power factor was calculated. We report a Seebeck value of $209 lV/K for Gd-doped GaN.

In this paper, room temperature thermoelectric (TE) properties of wide bandgap thin film GaN and bulk ZnO are studied. Bulk GaN is also incorporated with epitaxy films to make comparison. GaN and ZnO materials have superior electrical performance and chemical stability at high temperatures and are currently found in many commercial applications, such as, photovoltaic, solid‐state lighting, and gas sensors. Since there are not many semiconductor materials that can operate effectively at high temperatures, wide bandgap materials like GaN and ZnO would be a promising solution for high temperatures thermoelectric power generation. In order to understand their TE properties, we systematically compared and characterized TE behaviour of GaN and ZnO thin films with a function of doping concentrations. The common trend of a decrease in Seebeck coefficients with the increase of carrier concentration for thin film and bulk GaN is observed, however, reverse TE trend for bulk ZnO, were observed. The most commonly observed TE trend is attributed to Mott‐Jones relation to simple transport models while inverse trend could be suggested as hopping conductance. Moreover, the Seebeck coefficients of ZnO samples are found to be larger than those of thin film and bulk GaN samples in the similar carrier density. Highest power factors, 2.6×10–4 W/mK2and 0.65×10–4 W/mK2, and Seebeck coefficients, 478 µV/K and 481 μV/K were measured for thin film GaN and bulk ZnO, respectively. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The III-Nitrides are promising candidate for high efficiency thermoelectric (TE) materials and devices due to their unique features which includes high thermal stability. A systematic study of the room temperature TE properties of metalorganic chemical vapor deposition grown InxGa1-xN were investigated for x =  0.07 to 0.24. This paper investigated the role of indium composition on the TE properties of InGaN alloys in particular the structural properties for homogenous material that did not show significant phase separation. The highest Seebeck and power factor values of 507 μV K−1 and 21.84 × 10−4 Wm−1K−1 were observed, respectively for In0.07Ga0.93N at room temperature. The highest value of figure-of-merit (ZT) was calculated to be 0.072 for In0.20Ga0.80N alloy at room temperature.