Semiconductor-based Terahertz Traveling Wave Amplifiers for Monolithic Integration

Monolithic integration of terahertz (THz) amplifiers can pave way to miniaturization and mobility of many terahertz systems. In this project PIs propose a new configuration of terahertz amplifiers which can use traveling-wave phenomenology to provide terahertz gain in semiconductor media. Traveling wave gain occurs due to a synchronous interaction between moving charged particles and electromagnetic waves in its vicinity.

Classically, this phenomenology has provided amplification of electromagnetic waves in a large array of vacuum electron devices (e. g. vacuum-electronics based travelling wave amplifier). Notably, translation of this phenomenon into semiconductor media and its scaling to sub-millimeter dimensions is highly desirable. This is because of the possibility of obtaining similar gains and a high output power within microwave monolithic integrated circuits (MMICs).

This proposal will address new computing algorithms, material optimizations and device configuration innovations to create high gain amplifier topologies in 0.1 to 3 THz range based on electron-wave dynamics in semiconductor materials. This project aims at (1) introducing efficient numerical modeling tools to unveil the underlying complex phenomenology of electron-wave interactions in semiconductor materials and (2) investigating and validating the device concepts that exploit a synchronous electron-wave interaction for a THz wave amplification.

Overall, the project will broadly impact the medical, security, and wireless-communication areas, and benefit the national infrastructure of security and defense resiliency through its impact on wireless communication and imaging technology. The project further supports workforce development through training and education of one graduate student and three undergraduate students via the summer internship program.

The research outcomes as well as new scientific knowledge created from this proposal will be tied to the curriculum development by the PIs at UNL.

The specific scientific innovations of the project will be focused on advancements of multiphysics, multiscale numerical solvers, material and device-configuration innovations, and experimental validation of the amplifier through fabrication and measurements. To reach an optimized device PIs exploit naturally confined 2D electron gas in high electron mobility transistors (HEMTs) and in other confined electron-gas systems for creating a gain media for terahertz electromagnetic waves.

This is achieved by augmentation of slow-wave structures near 2D confined media to provide electron-wave interactions and amplification of THz waves. To model this problem, the project will first address the low computational efficiency and accuracy of current multiscale multiphysics global models. Project will specifically introduce time-domain numerical solvers that are based on multi-domain use of unconditional stability for gaining time-advantage and iterative corrections to maintain the accuracy.

PIs will adapt Alternate Directional Implicit (ADI) and iterative ADI algorithm for their integration into multiphysics finite different time domain method to provide up to an order more efficient numerical solver. Secondly, the project will use the proposed solvers towards developing behavioral models, material, and geometry optimizations, and thus provide first estimates of power, gain, and bandwidth through these studies.

Numerical studies will be used to optimize the devices for fabrication and measurements. In this context, the study will expansively investigate electromagnetic slow-wave structures, numerically model classical and new emerging material systems, and provide novel adaptation of the device concepts such as by using 2DEG-bilayer and superlattice. To validate the device concept, cold-tests are proposed in Ka-band, and device prototyping and measurements are proposed in W-band.

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.