GaN-Based IMPATTs for Microwave and Millimeter-Wave Generation
Abstract
GaN-Based IMPATTs for Microwave and Millimeter-Wave GenerationShort Statement of WorkThis project will investigate GaN-based IMPATT diodes for microwave through millimeter-wave frequency generation, made possible by leveraging the state-of-the-art epitaxial material growth techniques, in combination with fabrication of scaled devices (for high frequency operation). A 36 month program consisting ofi.) efforts in enhancing fundamental physical understanding of avalanche and breakdown in III-N materials and heterostructures.ii.) device design and simulation, including both electrical and thermal effectsiii.) process optimization and device fabricationiv.) device characterization and demonstration of IMPATT-based oscillators is proposed.ObjectiveExplore the fundamental physics of impact ionization processes in GaN, as well as to develop and demonstrate GaN-based IMPATT diodes for microwave through millimeter-wave frequency generation.ApproachFundamental physical understanding:p+/i/n+ homojunction and heterojunction structures will be characterizedas a function of peak internal electric field, i-layer thickness, and temperature. Devices will be grown homoepitaxially on bulk GaN substrates in order to achieve sufficiently low dislocation density that the device breakdown is material (vs. defect) limited. Intrinsic layer thickness studies will permit determination of impact ionization ~dead zone~ thickness in nitrides, as well as more rigorous determination of ionization coefficients for vertical transport in nitrides (much of the current literature in this area is clouded by defect-related effects, or has been extracted from lateral, rather than vertical, device structures). The impact of layout-dependent effects (e.g. area vs. periphery effects, etc.) will be investigatedto evaluate the impact of edge defects, quality of junction termination, etc., and its role in device performance. Device design and simulation: Device designs based both on analytical analysis and detailed simulation (Monte Carlo) will be developed. The design process will be iterative, based on experimental data (acquired from fundamental studies as well as previous device results). Projections of expected performance (frequency of oscillation, maximum power handling) and figures of merit will be extracted. Key design variables include the details of the avalanche region (based on behavior extracted from the ~fundamental study~ task above), the drift layer thickness and doping profile, device area and layout (to minimize parasitics and edge effects), and edge termination configuration.Thermal simulations will also be performed to clarify the role and limitations imposed by heat generation in the devices. Projections for packaging requirements, etc., will be developed. Homojunction designs (varying peak internal electric field, intrinsic avalanche layer thickness, and drift layer thickness) will be explored initially, followed by heterostructure designs incorporating hot-carrier injection (to lower the impact ionization threshold and dead zone thickness). The effort plans for 4-5 heterostructure designs per year to be comprehensively evaluated in the program. Process optimization and device fabrication: The device designs developed will be fabricated experimentally using the cleanroom facilities at Notre Dame. Additional efforts are planned primarily in the area of edge termination (validation and optimization, needed primarily to allow exploration of devices with breakdown voltages > 400 V) and p-type contacts (needed to optimize device DC-to-RF conversion efficiency). Device characterization and demonstration of oscillators: Fabricated devices will be tested at DC and RF over temperature. Characterization will include DC I-V and CV to confirm basic device layer structure and intended field profiles, temperature dependent DC I-V to confirm avalanche-dominated breakdown, on-wafer s-parameters to confirm the presence of negative differential conductance, and ultim
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 23, 2016
- Source ID
- N000141612850
Entities
People
- Patrick Fay
Organizations
- Office of Naval Research
- United States Navy
- University of Notre Dame