NER: Enhancement of the Efficiency of Thermoelectric Devices via Engineering of the Electron-Phonon Interaction in Quantum Dot Superlattices

该提案是为响应国家科学与工程计划，NSF 01-157计划而提出的。提出了一种通过调节多个半导体量子点阵列中的电子-声子相互作用来提高半导体材料热电优值ZT的新方法。量子点阵列是热电“电子传输-声子阻挡”材料的潜在候选者。同时，为了实现ZT的显著改善并与传统的热电材料竞争，人们必须设计和制备量子点超晶格，其中载流子的传输通过形成载流子微带来促进。事实上，随机量子点阵列中的横向载流子传输的典型跳跃电导具有非常低的载流子迁移率，而微带传输可能导致非常高的迁移率值，特别是如果人们通过智能微带工程设法至少部分地抑制载流子散射的话。该方案的重要任务是从理论上验证量子点超晶格中实现微带输运机制和抑制载流子散射的条件.由于空间限制和边界散射的影响，量子点阵列中声子模的改变导致声子态密度的改变，声子群速度的降低，以及面内晶格热导率的相应下降.声学声子限制，例如由于纳米结构边界引起的声子色散的改变，与载流子限制效应相比，研究得更少。同时，它还可以作为一种辅助工具来降低晶格热导率，提高热电器件的效率。因此，该项目的另一项任务是研究实现理想的声学声子传输特性所需的结构参数，例如，点大小、形状、声学失配等，例如沿着感兴趣的方向的低群速度；共振声子散射条件；声子池与电子的去耦合等。基于纳米结构材料的新型高效热电器件由于其高可靠性、轻质、紧凑、退出操作和环境安全等固有优势，可能对广泛的能源需求产生巨大影响。

This proposal was received in response to the National Science and Engineering Initiative, Program Solicitation NSF 01-157, in the NER category. The proposal focuses on a new approache to enhancement of the thermoelectric figure of merit ZT of semiconductor materials via tuning of electron-phonon interaction in multiple arrays of semiconductor quantum dots. Quantum dot arrays are potential candidates for the thermoelectric "electron transmitting - phonon blocking" material. At the same time, in order to achieve a significant ZT improvement and compete with conventional thermoelectrics one has to design and fabricate quantum dot superlattice where carrier transport is facilitated by the formation of carrier mini-bands. Indeed, hopping conductivity typical for lateral carrier transport in random quantum dot arrays has very low carrier mobility while mini-band transport may lead to very high mobility values, particularly if one manages to suppress at least partially the carrier scattering via smart mini-band engineering. The important task addressed in this proposal is theoretical proof-of-concept investigation of requirements for achieving mini-band transport regime and carrier scattering suppression in quantum dot superlattices.Modification of acoustic phonon modes in quantum dot arrays due to spatial confinement and boundary scattering leads to a change in the phonon density of states, a decrease of the phonon group velocity, and corresponding drop of the in-plane lattice thermal conductivity. Acoustic phonon confinement, e.g. modification of phonon dispersion due to nanostructure boundaries, is much less researched phenomenon than carrier confinement effect. At the same time, it can serve as an additional tool to decrease the lattice thermal conductivity value and increase the effectiveness of the thermoelectric device. Thus, another task of this project is a study of the required structure parameters, e.g. dot size, shape, acoustic mismatch, etc., for achieving desirable acoustic phonon transport features such as low group velocity along direction of interest; resonant phonon scattering conditions; decoupling of phonon bath from electrons; etc. New efficient thermoelectric devices based on nanostructured materials may have a tremendous impact on a wide range of energy needs due to their inherent advantages such as high reliability, light weight, compactness, quit operation, and environmental safety.