Ultrafast Nano-optic probes for Wide Bandgap Semiconductor characterization
Abstract
The push towards all-electrical systems in the US DoD, including the All-Electric Navy Initiative, has driven the development of semiconductor materials suitable for operation under high power, temperature, and other harsh conditions. This is further motivated bythe desire for high-power electronics within the automotive and power distribution sectors of the US economy. Materials such as gallium nitride (GaN) offer the potential for significant improvements over the state-of-the-art. However, despite advancements in the quality of substrates, epilayers, and device processing, the potential for GaN in power electronics remains to be realized. Criticalto improving GaN devices is understanding the properties and imperfections of the material itself, both in epitaxial layers and in devices, including when such devices are in operation. Understanding the role of epilayer defects, bulk dopants, and implanted dopants with respect to electrical performance is especially important. For vertical GaN devices, these properties must be understood notjust as a function of lateral position on the wafer, but also depth under the surface, extending into the active layers of these devices, and must also be quantified under dynamic operation. Current characterization approaches cannot meet all these requirements for GaN. Novel metrologies and methods are required to advance our understanding of GaN and other emerging WBG semiconductors. We propose that ultrafast, nano-optic, and temperature-dependent infrared (IR) probes can overcome these challenges and thereby advance our understanding of WBG semiconductor materials and devices. We propose three key tasks:1) Study the lateral profile and impact of defects and dopants in GaN devices and materials. We will apply knowledge gained from bulk infrared spectroscopy toward the understanding of these effects at the micro-and nanoscales for dopant, strain, and defect imaging. We will explore far-field and near-field phonon-driven absorption/reflection processes, including SPhP modes, and correlate performance with known electrical characterization.2) Evaluate the vertical profile and impact of defects and dopants in GaN devices and materials. We will leverage depth sensitivityof polaritons and cross-sectioning to examine the properties of the implantation induced material modifications and to characterizethe active regions of GaN devices. This will provide direct access to doping profiles and defect distributions within the active regions of the device. We will then establish the depth sensitivity of polaritons to vertically implanted dopants and defects excited from the top of the GaN epilayers using prism-based spectroscopy. 3) Determine the role of temporal changes to doping and defects inGaN devices and materials. We will use ultrafast nano-optic probes to understand the differences in dynamic versus static behavior of GaN devices and materials. We will employ FTIR modulation spectroscopy and multiphoton absorption # where a periodic electrical signal or optical pulse is directly passed through a device, and changes in the infrared spectrum are measured. Our second approach will leverage ultraviolet pump-probe near-field spectroscopy to dynamically track changes in the properties of a material with nanoscale spatial resolution and s-SNOM measurements under device bias conditions. At the end of this work, we will have demonstrated the potential for infrared probes for imaging and quantifying the electronic, optical, and phonon behaviors of emerging WBG materials. We will demonstrate these tools for non-destructive, non-contact electrical characterization of future WBG semiconductors, as well asthe local impact of extended defects upon these properties. Beyond the implications for electronic materials, these efforts will also have significant impact upon IR nanophotonics, thermal characterization, and non-linear optics, impacting several ONR areas of interest. Approved for Public Release
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 24, 2023
- Source ID
- N000142312676
Entities
People
- Joshua Caldwell
Organizations
- Office of Naval Research
- United States Navy
- Vanderbilt University