Resonant Energy Transfer Based Electrically Pumped Hybrid Lasers

利用廉价、溶液可加工的材料，实现具有低阈值电流密度和可调谐发射波长的紧凑可靠的电泵激光器，将对包括光子学、化学传感和医学诊断在内的许多学科产生革命性的影响。胶体半导体量子点（CQDs）是实现这一目标的有吸引力的纳米材料，因为它们可以使用易于扩展的化学技术制造，并且它们的光学性质可以通过量子限制效应直接控制。与其他方法相比，CQDs通过表面修饰和形成CD异质结构，提供了几乎无与伦比的高度可控结构特性的灵活性。然而，CQD薄膜的载流子迁移率低和导热性差是目前其在电泵浦激光器中应用的主要挑战。提出的项目专门解决了这些挑战，并为基于由外延Si/SiGe纳米层和pb基CQD薄膜组成的混合纳米结构中的谐振能量转移（RET）的新型相干光源的开发提供了有希望的解决方案。该研究项目的进展将通过出版物、会议报告、学术课程、本科生和研究生的研究经历以及为当地高中生提供的暑期项目广泛传播。RET是一种通过偶极-偶极相互作用从能量供体到受体的短程非辐射共振能量传递过程。通常情况下，RET与不良的能量反转移（EBT）共存，但本项目提出的器件设计和纳米材料的选择应抑制EBT。此外，外延Si/SiGe纳米结构中的载流子迁移率和热导率比CQD薄膜好几个数量级，并且载流子注入水平有望足以实现种群反转。此外，所提出的方法特别侧重于混合纳米结构，旨在使RET速率比能量松弛的竞争过程（如俄歇和缺陷相关的载流子重组）大几个数量级。为了实现这一目标，将利用合成化学的进展，开发具有高度可控制界面组成的新型基于铅的核-壳CQDs，并允许具有原子单层厚度的壳外延覆盖QD核心。在这些成分控制的核-壳CQDs中，俄歇复合有望被抑制，并可以实现有利的光放大条件。此外，提出的研究还解决了电泵浦CQD激光器的其他关键问题，包括载流子注入器的设计、出口位置的控制和低缺陷密度界面的形成。预期的结果将有助于实现具有不同组成的量子点的基于电抽运cqd的激光器，并为开发多种应用的新型相干光源提供了一条有希望的途径。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Realization of electrically pumped compact and reliable lasers with low-threshold current densities and tunable emission wavelengths made from inexpensive, solution processable materials will have a revolutionary impact on many disciplines including photonics, chemical sensing, and medical diagnostics. Colloidal semiconductor quantum dots (CQDs) are attractive nanomaterials for achieving this goal because they can be fabricated using easily scalable chemical techniques, and their optical properties can be directly controlled via the quantum confinement effect. Compared to other approaches, CQDs offer practically unmatched flexibility of highly controllable structural properties by using surface modifications and formation of CD heterostructures. However, low carrier mobilities and poor thermal conductivity of CQD thin films are currently the major challenges for their applications in electrically pumped lasers. The proposed project specifically addresses these challenges and offers promising solution for the development of novel coherent light sources based on resonant energy transfer (RET) in hybrid nanostructures comprised of epitaxial Si/SiGe nanolayers and Pb-based CQD thin films. Advances from this research project will be disseminated widely through publications, conference presentations, academic courses, undergraduate and graduate student research experience and summer programs for local high school students. RET is a short-range non-radiative resonant energy transfer process from an energy donor to acceptor via dipole-dipole interaction. Normally, RET co-exists with the undesirable energy back transfer (EBT), but the proposed in this project device design and choice of nanomaterials should suppress EBT. In addition, charge carrier mobility and thermal conductivity in epitaxial Si/SiGe nanostructures are orders of magnitudes better compared to that in CQD thin films, and the level of carrier injection is expected to be sufficient to achieve population inversion. Also, the proposed approach is specifically focused on hybrid nanostructures designed to make the RET rate orders of magnitudes greater compared to competing processes of energy relaxation, such as Auger and defect related carrier recombination. To achieve this goal, novel Pb-based core-shell CQDs with highly controllable interface composition will be developed using advances in synthetic chemistry and allowing epitaxial coverage of a QD core by a shell with a thickness of an atomic monolayer. In these composition-controlled core-shell CQDs Auger recombination is expected to be suppressed and favorable conditions for optical amplification can be achieved. In addition, the proposed research addresses other key issues for electrically pumped CQD lasers including design of carrier injectors, control over exiton locations and formation of low-defect density interfaces. The anticipated results will contribute to realization of electrically pumped CQD-based lasers with QDs of different compositions and provide a promising route for the development of novel coherent light sources for multiple applications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.