Large enhancements of thermopower and carrier mobility in quantum dot engineered bulk semiconductors.

The thermopower (S) and electrical conductivity (σ) in conventional semiconductors are coupled adversely through the carriers' density (n) making it difficult to achieve meaningful simultaneous improvements in both electronic properties through doping and/or substitutional chemistry. Here, we demonstrate the effectiveness of coherently embedded full-Heusler (FH) quantum dots (QDs) in tailoring the density, mobility, and effective mass of charge carriers in the n-type Ti(0.1)Zr(0.9)NiSn half-Heusler matrix. We propose that the embedded FH QD forms a potential barrier at the interface with the matrix due to the offset of their conduction band minima. This potential barrier discriminates existing charge carriers from the conduction band of the matrix with respect to their relative energy leading to simultaneous large enhancements of the thermopower (up to 200%) and carrier mobility (up to 43%) of the resulting Ti(0.1)Zr(0.9)Ni(1+x)Sn nanocomposites. The improvement in S with increasing mole fraction of the FH-QDs arises from a drastic reduction (up to 250%) in the effective carrier density coupled with an increase in the carrier's effective mass (m*), whereas the surprising enhancement in the mobility (μ) is attributed to an increase in the carrier's relaxation time (τ). This strategy to manipulate the transport behavior of existing ensembles of charge carriers within a bulk semiconductor using QDs is very promising and could pave the way to a new generation of high figure of merit thermoelectric materials.

[1]  F. Aliev,et al.  Gap at the Fermi level in the intermetallic vacancy system RBiSn(R=Ti,Zr,Hf) , 1989 .

[2]  V. Moshchalkov,et al.  Narrow band in the intermetallic compounds MNiSn (M=Ti, Zr, Hf) , 1990 .

[3]  Donald T. Morelli,et al.  Transport properties of pure and doped M NiSn ( M =Zr, Hf) , 1999 .

[4]  R. Venkatasubramanian,et al.  Thin-film thermoelectric devices with high room-temperature figures of merit , 2001, Nature.

[5]  M. P. Walsh,et al.  Quantum Dot Superlattice Thermoelectric Materials and Devices , 2002, Science.

[6]  M. Kanatzidis,et al.  Cubic AgPbmSbTe2+m: Bulk Thermoelectric Materials with High Figure of Merit , 2004, Science.

[7]  S. Sakurada,et al.  Effect of Ti substitution on the thermoelectric properties of (Zr,Hf)NiSn half-Heusler compounds , 2005 .

[8]  Electronic structure and magnetism in doped semiconducting half-Heusler compounds , 2005, cond-mat/0611478.

[9]  G. Fecher,et al.  Diluted magnetic semiconductors with high Curie temperature based on C1b compounds: CoTi1−xFexSb , 2006 .

[10]  Jonathan D'Angelo,et al.  High thermoelectric figure of merit and nanostructuring in bulk p-type Na1-xPbmSbyTem+2. , 2006, Angewandte Chemie.

[11]  H. Scherrer,et al.  Electronic structure and thermopower ofNi(Ti0.5Hf0.5)Snand related half-Heusler phases , 2006 .

[12]  O. Eriksson,et al.  Ferromagnetism in Mn doped half-Heusler NiTiSn: Theory and experiment , 2006 .

[13]  G. J. Snyder,et al.  Enhancement of Thermoelectric Efficiency in PbTe by Distortion of the Electronic Density of States , 2008, Science.

[14]  S. Poon,et al.  Electronic structure of transition metal-doped XNiSn and XCoSb (X = Hf,Zr) phases in the vicinity of the band gap , 2008 .

[15]  M. Dresselhaus,et al.  High-Thermoelectric Performance of Nanostructured Bismuth Antimony Telluride Bulk Alloys , 2008, Science.

[16]  S. Poon,et al.  (Zr,Hf)Co(Sb,Sn) half-Heusler phases as high-temperature (>700°C) p-type thermoelectric materials , 2008 .

[17]  G. J. Snyder,et al.  Complex thermoelectric materials. , 2008, Nature materials.

[18]  A. Gloskovskii,et al.  Thermoelectric properties of CoTiSb based compounds , 2009 .

[19]  M. Kanatzidis,et al.  New and old concepts in thermoelectric materials. , 2009, Angewandte Chemie.

[20]  Shuang Jia,et al.  Half-Heusler ternary compounds as new multifunctional experimental platforms for topological quantum phenomena. , 2010, Nature materials.

[21]  M. Kanatzidis.  Nanostructured Thermoelectrics: The New Paradigm?† , 2010 .

[22]  Claudia Felser,et al.  Tunable multifunctional topological insulators in ternary Heusler compounds. , 2010, Nature materials.

[23]  G. Fecher,et al.  Electronic transport properties of electron- and hole-doped semiconducting C1b Heusler compounds: NiTi1−xMxSn (M=Sc, V) , 2010 .

[24]  Ali Shakouri,et al.  Nanostructured Thermoelectrics: Big Efficiency Gains from Small Features , 2010, Advanced materials.

[25]  Wenguang Zhu,et al.  Half-Heusler compounds as a new class of three-dimensional topological insulators. , 2010, Physical review letters.

[26]  P. Poudeu,et al.  Effects of Ir Substitution and Processing Conditions on Thermoelectric Performance of p-Type Zr0.5Hf0.5Co1−xIrxSb0.99Sn0.01 Half-Heusler Alloys , 2011 .

[27]  C. Uher,et al.  Thermal and electronic charge transport in bulk nanostructured Zr0.25Hf0.75NiSn composites with full-Heusler inclusions , 2011 .

[28]  Claudia Felser,et al.  Simple rules for the understanding of Heusler compounds , 2011 .

[29]  Xianli Su,et al.  Simultaneous large enhancements in thermopower and electrical conductivity of bulk nanostructured half-Heusler alloys. , 2011, Journal of the American Chemical Society.

[30]  J. Sakamoto,et al.  A special issue on advanced thermoelectric materials and devices , 2011 .

[31]  P. Poudeu,et al.  Microstructure and Thermoelectric Properties of Mechanically Alloyed Zr 0.5 Hf 0.5 Ni 0.8 Pd 0.2 Sn 0.99 Sb 0.01 /WO 3 Half-Heusler Composites , 2011 .

[32]  M. Kanatzidis,et al.  Strained endotaxial nanostructures with high thermoelectric figure of merit. , 2011, Nature chemistry.

[33]  Heng Wang,et al.  Convergence of electronic bands for high performance bulk thermoelectrics , 2011, Nature.

[34]  P. Poudeu,et al.  Investigation of the Effect of NiO Nanoparticles on the Transport Properties of Zr 0.5 Hf 0.5 Ni 1– x Pd x Sn 0.99 Sb 0.01 ( x = 0 and 0.2) , 2011 .

[35]  M. Kanatzidis,et al.  High-performance bulk thermoelectrics with all-scale hierarchical architectures , 2012, Nature.

[36]  Timothy P. Hogan,et al.  Raising the thermoelectric performance of p-type PbS with endotaxial nanostructuring and valence-band offset engineering using CdS and ZnS. , 2012, Journal of the American Chemical Society.

[37]  Ye-Min Lu,et al.  High figure of merit in (Ti,Zr,Hf)NiSn half-Heusler alloys , 2012 .

[38]  Y. Kimura,et al.  Nanosized precipitates in half-Heusler TiNiSn alloy , 2012 .

[39]  P. Poudeu,et al.  Effect of NiTe Nanoinclusions on Thermoelectric Properties of Bi2Te3 , 2012, Journal of Electronic Materials.