Efficient GHz Surface-Normal Modulators for SWIR ToF Imagers

Project: Research project

Project Details


A.1. Program Plan We propose a 12-month program to simulate, design, epitaxially grow, process, and test efficient modulators that can achieve over 1 GHz bandwidth for SWIR Time of Flight (ToF) imaging. The target frequency is about 30 times higher than anything that is reported outside Northwestern. The project involves three iterations (spins) of device modeling/fabrication/test, which allows for rapid feedback needed for realization of high-speed modulators. Northwestern will work with a government/DoD lab to integrate the modulator in a SWIR ToF system. A Northwestern spinoff company, StarSight Inc., has been working on ToF imagers at the system-level for commercial applications, and would be able to efficiently utilize its expertise for the system integration. A.2. Tasks TASK-1: Modulator Design and Modeling  Task 1.1 - Modeling and optimization of quantum wells: we will expand our current model to self-consistently model the optical absorption versus external electric field and wavelength in complex quantum well designs. Although we have existing designs, they are solving for wavefunctions without inclusion of the Coulomb interactions.  Task 1.2 - Modeling of the devices: compared to the existing semiconductor-base GHz modulators, the proposed device has an area that is three orders of magnitude larger. Therefore, interaction of different properties such as thermal, mechanical, and quantum will be significant. We will use three-dimensional multi-physics simulation to concurrently model the electrical, thermal, and electro-optical properties of the device. We will optimize the design for the first fabrication spin, and then fine tune the model based on measured results (TASK-3, TASK-4, and TASK-5) to further optimize the design for the second and third spins. TASK-2: Epitaxial Growth and Characterization  Task 2.1 - Epitaxial growth design: Northwestern has significant expertise in designing the gas flow sequence in MOCVD, and shutter sequence in MBE systems, for optimum interface between heterojunctions. In particular, the structures of interest include antimonide-based layer which are known to be sensitive to the transition layers. Mohseni’s group has been closely working with epitaxial growers at Sarnoff-SRI for the past 12 years, and successfully designed and produced complex semiconductor structures - including some of the best reported quantum cascade lasers, QWIP, and type-II heterojunctions.  Task 2.2 - Epitaxial growth and characterization: We will subcontract Sarnoff-SRI for the epitaxial growth of GaInAsP/GaInAsSb/AlInAs/InP modulator structures. Sarnoff will also perform structural, electrical and optical characterization of the grown epitaxial layers. These include x-ray diffraction, secondary ion mass spectrometry (SIMS), Hall measurement, CV characterization, and photoluminescence. TASK-3: Modulator Processing  Task 3.1 - Microfabrication: Northwestern will fabricate modulators with exceedingly higher speed through three spins. In particular, we will produce extremely low contact resistance based on special alloys deposition and processing, as well as very thick metal connectors to distribute the power efficiently across the device. We will also develop transparent conductive layers to significantly enhance the lateral conductivity needed for high-speed large area devices, and develop anti-reflection coatings with large FOV.  Task 3.2 - Device probe-testing: We will test devices during the processing using our unique probe-station, which allows optical and high-speed electrical probing from 400 K do
Effective start/end date8/22/165/31/18


  • Army Research Office (W911NF-16-1-0458)


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