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Progress towards a Mid-Infrared Single Photon Source
Published in J Kono, J Léotin, Narrow Gap Semiconductors, 2006
G.R. Nash, S.J. Smith, C.J. Bartlett, M.K. Haigh, N.T. Gordon, H.R. Hardaway, J. Edwards, L. Buckle, M.T. Emeny, T. Ashley
Narrow gap semiconductors, such as InSb, have many interesting properties that make them attractive for a wide range of electronic and optical applications. For example, the high electron mobility has been utilised in the fabrication of high speed transistors [13], whilst the small direct energy gap and high ratio of stimulated to spontaneous emission rates has led to the fabrication of high power IR lasers [14], In particular, the small effective electron mass, which in InSb is approximately a fifth of that in GaAs, also offers the possibility to fabricate room temperature quantum devices due to the enhanced quantum confinement. However, it’s only in the last few years that it has become possible to grow InSb/InAISb heterostructures of sufficient quality that a high mobility two-dimensional electron gas (2DEG) forms at the interface [13,15]. The measurements described in this paper were made on samples fabricated from InSb/InAISb quantum well structures grown by molecular beam epitaxy on semi-insulating GaAs substrates, where tellurium and beryllium were used to dope the layers n-type and p-type respectively. Further details of the growth can be found in [13].
Low-Temperature Thermoelectric Materials
Published in Zhifeng Ren, Yucheng Lan, Qinyong Zhang, Advanced Thermoelectrics, 2017
Koen Vandaele, Joseph P. Heremans, Yiming Zhou, Li-Dong Zhao, Huaizhou Zhao, Zhifeng Ren, Machhindra Koirala, Stephen R. Boona
As prepared directly from the synthesis, the room-temperature conductivity and Seebeck coefficient of the single crystals of CsBi4Te6 are in the range of 900–450 S/cm and 90–150 μV/K. The properties distribute in a range due to the impurities. So all these kinds of materials are called as-prepared rather than undoped. All those as-prepared samples are invariably p-type, which is indicated by the positive Seebeck coefficient. The weak temperature dependence of conductivity as well as the large value of the Seebeck coefficient and its positive temperature dependence correspond to the behaviors of a degenerate narrow-gap semiconductor.
Ab Initio-Based Band Engineering and Rational Design of Thermoelectric Materials
Published in D. M. Rowe, Materials, Preparation, and Characterization in Thermoelectrics, 2017
Jiong Yang, Xun Shi, Wenqing Zhang, Lidong Chen, Jihui Yang
DFT-based ab initio methods have been widely used in understanding the fundamental properties of materials nowadays, covering structural energetics, electronic structures, and various functionalities. Good TE materials are traditionally considered to be narrow-gap semiconductors. From this point of view, DFT-based band structures can be greatly helpful to a rational search for novel materials. Such an approach has been followed by many people working in the TE community.
Data-driven analysis of electron relaxation times in PbTe-type thermoelectric materials
Published in Science and Technology of Advanced Materials, 2019
Yukari Katsura, Masaya Kumagai, Takushi Kodani, Mitsunori Kaneshige, Yuki Ando, Sakiko Gunji, Yoji Imai, Hideyasu Ouchi, Kazuki Tobita, Kaoru Kimura, Koji Tsuda
Although first-principles calculation is a powerful tool to select many candidate thermoelectric materials [7,8], various kinds of uncertainties arise in predicting actual thermoelectric properties [9]. Calculations usually examine idealistically clean crystals, whereas experimental high-ZT samples are much dirtier. The errors in band gap values create huge errors in calculating Seebeck coefficients in many high-ZT compounds, which are narrow-gap semiconductors. Calculations employing Boltzmann’s transport equation cannot calculate σ and κel directly; they can only evaluate σ/τel and κel/τel, where τel is an unknown variable called the electron relaxation time. As τel is the time between electron scattering, long τel is expected in PGEC materials. Although many studies assume constant τel (often at 10−14 s), a large sample dependence of τel is reported in a few studies [9,10].
Data-driven analysis of electron relaxation times in PbTe-type thermoelectric materials
Published in Science and Technology of Advanced Materials, 2019
Yukari Katsura, Masaya Kumagai, Takushi Kodani, Mitsunori Kaneshige, Yuki Ando, Sakiko Gunji, Yoji Imai, Hideyasu Ouchi, Kazuki Tobita, Kaoru Kimura, Koji Tsuda
Although first-principles calculation is a powerful tool to select many candidate thermoelectric materials[7,8], various kinds of uncertainties arise in predicting actual thermoelectric properties[9]. Calculations usually examine idealistically clean crystals, whereas experimental high-ZT samples are much dirtier. The errors in band gap values create huge errors in calculating Seebeck coefficients in many high-ZT compounds, which are narrow-gap semiconductors. Calculations employing Boltzmann’s transport equation cannot calculate σ and κel directly; they can only evaluate σ/τel and κel/τel, where τel is an unknown variable called the electron relaxation time. As τel is the time between electron scattering, long τel is expected in PGEC materials. Although many studies assume constant τel (often at 10−14 s), a large sample dependence of τel is reported in a few studies[9,10].