Ultrafast Shift-Current Photodetection Using Polar Group IV Chalcogenide van der Waals Semiconductors and Heterostructures (b. Engineering Sciences, ii. Electronics, (3) Electronic Sensing Program)
Abstract
Conventional photodetectors use light absorption to excite electron-hole pairs that are separated by an electric field, usually at a pn- or pin-junction, to produce an electrical signal. Although this photovoltaic effect has been harnessed successfully for photodetection across a wide spectral range and to bandwidths exceeding 200 GHz, fundamental tradeoffs between sensitivity and response time limit its further development for ultrafast detection of pulsed light. The shift current (or more generally the bulk photovoltaic effect) in homogeneous semiconductors with broken inversion symmetry provides a fundamentally different mechanism for light-to-electrical transduction in photodetectors. Shift currents rely on a topological effect, where the geometric (Berry) phase of the electron wavefunction in momentum space represents a real space displacement in the center of mass of electron wavepackets. Attractive characteristics include simplicity in device design (no junctions), insensitivity to impurities and defects, suppression of shot noise, potentially large signals (photovoltages can exceed the bandgap of the semiconductor), and ultrafast (picosecond-scale) response to pulsed light. But despite these promising attributes, shift currents have been considered primarily for energy conversion and investigations of their potential for photodetection remain in their infancy. The research proposed here lays the foundation for addressing the challenge of creating ultrafast infrared photodetectors with picosecond response times, using shift currents in non-centrosymmetric semiconductors and heterostructures as detection mechanism. The research breaks new ground in conducting experiments that provide a fundamental understanding of shift current generation, and of its opportunities and challenges for photodetection. Other goals include exploring non-centrosymmetric van der Waals semiconductors and heterostructures as materials for shift current photodetection, and identifying novel avenues for extending the shift current response to longer infrared wavelengths. To pursue these goals, the project focuses on a particular class of materials, layered group IV chalcogenide semiconductors and heterostructures. Monolayers of group IV monochalcogenides (MX, where M: Ge, Sn; X: S, Se) are polar, ferroelectric semiconductors and have been theoretically predicted to show strong shift current response. But single atomic layers are challenging to obtain for these materials and their interaction with light is likely too weak to create sensitive photodetectors. Our recent results showed that these issues can be overcome by growing thicker (multilayer) crystals in which the non-polar (A-B) equilibrium stacking is replaced by a metastable (A-A) layer stacking sequence that breaks inversion symmetry. Furthermore, we demonstrated that interfacial light absorption at type II heterojunctions between these materials provides electronic excitations with threshold energy below the constituent bandgaps. The proposed research seizes upon these opportunities by pursuing three interconnected scientific thrusts: i) Development of the controlled synthesis of non-equilibrium stacked MX crystals and heterostructures; ii) measurements of their fundamental optoelectronic properties; and iii) shift-photocurrent spectroscopy on devices built from polar MX crystals, alloys, and heterostructures. If successful, the work will lead to photodetectors that rely on light-to-electrical signal transduction mechanisms that are fundamentally different from the conventional electric field driven excited carrier separation/collection, operate at room temperature, and offer avenues toward detecting infrared light with ultrafast temporal impulse response times.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 08, 2023
- Source ID
- W911NF2310060
Entities
People
- Eli Sutter
Organizations
- Army Contracting Command
- United States Army
- University of Nebraska–Lincoln