Thermoelectric properties of Tin Telluride Thin Films Grown using Pulsed Laser Deposition

• Main Authors: Huang, Jun-Jie, 黃俊傑
• Other Authors: Leu, Jihperng
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/28815630107729370356

碩士 === 國立交通大學 === 材料科學與工程學系所 === 103 === Tin telluride (SnTe), a lead-free narrow band gap IV-VI semiconductor, is an environment friendly and a potential substitution material of the well-known lead chalcogenides for thermoeletric (TE) power generator in middle range temperatures (600 – 900 K). In this study, nanostructured p-type SnTe thin films were grown on SiO2/Si (100) substrates using pulsed laser deposition (PLD) at substrate temperatures (Ts) from 25 to 400 oC under an argon gas pressure of 220 mTorr. Effects of the films structure, composition, and morphology on the room-temperature TE properties were systematically studied. The morphologies exhibited nanotriangulars at Ts, 25 – 120 oC, nanocolumns at 200 oC, nanoleaves at 250 oC, nanosculptures at 300 oC, nanotetris at 350 oC, and compact-polycrystalline at 400 oC. A composition of slightly Sn-rich suppressed Sn vacancies, resulting in a low hole concentration of Np ~ 1020 cm-3. The Seebeck coefficient was considerably enhanced as compared with the theoretical prediction, due to (1) the enhancement of density of states as lowering the Fermi level to have simultaneously contribution of the well-known two-valence (L+Σ) bands of SnTe, and (2) the distinctive nanostructures. Moreover, the hole mobility (µ) monotonically increased from 0.37 cm2/Vs (for nanotriangular) to 345.2 cm2/Vs (for compact-polycrystalline) with increasing Ts from 25 to 400 oC. The increasing µ with Ts can be attributed to the decreasing Np (defects), the slightly increasing grain size, and the improved crystallinity with increasing Ts. At Ts of 250oC, the nanoleaves film possessed the best Seebeck coefficient (41.1 µV/K) in conjunction with the best TE power factor (PF), 3.53 µWcm-1K-2, where σ = 2089 Scm-1. The nanostructures such as nanoleaves are beneficial in reducing the lattice thermal conductivity due to the extensive phonon scattering at grain boundaries. As a result, nanostructured SnTe thin films have been demonstrated their promises for enhancing the figure of merit (ZT) and TE applications.