Evolutionary development of a new generation of extreme RF (x-RF) electronics at frequencies >100 GHz and high power based on known approaches requires a Johnson������������������s figure of merit (JFOM) orders of magnitude superior to that of wide bandgap materials such as GaN. The two main material properties that the JFOM considers are critical breakdown field and drift saturation velocity. Novel ultra-wide bandgap (UWBG) materials with high critical breakdown fields satisfy the first part of the equation. The saturation velocity limit, however, which determines the transit times and frequency limits, cannot be easily overcome. This is due to the nature of bonding in UWBGs, leading to high optical phonon scattering rates and significant related energy losses. It is clear that classical steady-state transport and scaling alone cannot provide for the desired frequency range and targeted power performance. As such, the governing hypotheses of the proposed Center for ultra-wide bandgap extreme-RF electronics (CUXRFE) are: ��������� High fields in UWBG materials allow for transport conditions beyond the classical steady state transport, such as ballistic transport or velocity overshoot of electrons or other quasi-particles, and allow for short transit times unattainable by scaling alone. ��������� In order to exploit intrinsic transient transport phenomena, extrinsic barriers to device performance must be addressed . These include contacts, surfaces, and interfaces required to support high field transport and short transit times.

Power semiconductor devices are critical for the energy infrastructure as it is projected that by 2030 as much as 80% of the electricity generated will pass through one or more power conversion stage from generation to consumption (30% over today). Maximizing the energy efficiency of switching semiconductor devices in these power conversion stages is, therefore, of utmost importance. III-Nitride-based high power switches are understood to be the building blocks of future low loss power grids. Schottky power devices with breakdown fields exceeding 1000 V and currents > 10 A have been reported for GaN based lateral and vertical devices. However, despite these positive and encouraging results, wide bandgap power switches have not reached a significant market penetration due to concerns related to the ultimate performance and lifetime of the devices. Improvements in the achievable breakdown fields and current, turn-on voltage and on-resistance, and lifetime of wide bandgap power switches are typically achieved by: (a) reduction of extended defects such as dislocations, (b) control of doping and compensation in the drift layers, and (c) optimization of the device design and fabrication. In order to achieve the best device performance including lowest on resistance and highest breakdown fields, an accurate control of the materials properties is needed. While GaN power diodes are already under development and have proven their potential to disrupt the market, research needs to be initiated that targets the second next generation of power diodes and switches. A potential candidate to achieve even higher BFOM than GaN, SiC, and Si (and GaO) is AlN and Al-rich AlGaN.

Charged point defects in compound semiconductors strongly determine electronic and optical properties. The energy of formation of a point defect is a function of the process conditions and the Fermi energy. In wide bandgap semiconductors or insulators, the contribution of the Fermi energy to the formation energy of charged point defects is significant. For the practical case of doping for n- or p-type conductivity, the larger the energy gap, the higher the concentration of compensating point defects that is at equilibrium with the system. This is a fundamental problem with wide bandgap materials that will be directly addressed with these capabilities. In this approach, we will extend the concept of the quasi-Fermi level in an effort to quantify the impact of external excitation in the formation energy of the point defect. Increasing the formation energy of unwanted point defect through external excitation during a growth experiment leads to a reduction in compensating point defects. Many applications such as optoelectronics and power electronics rely on the functionality of wide bandgap materials. But to reach their full potential, it is necessary to realize point defect control in order to enhance the doping capabilities. This research will directly lead to materials that will be used for applications that deal with the preservation and extension of natural resources by allowing for: (1) the efficient use and transmission of electrical energy, (2) the availability of clean potable water through disinfection by the use of UV LEDs, and (3) the detection of pollutants and other effluents. The novel concepts developed within this project can also be implemented in the educational and outreach efforts (some specifically targeted at minority students), especially integrating point defect characterization and control schemes to applications dealing with the need for the development of materials for sustainability purposes. The students involved in this research will have access to my international collaboration network and exposure, giving the students the opportunity to build an international network for establishing their future career.

The objective of this project is to develop a compact and efficient avalanche photodiode (APD), operating between 210-280 nm, for implementation in the next generation bio-chem-detectors. The proposed detectors will be based on the AlGaN materials system and will be solar blind, highly sensitive, smaller, less expensive, and more robust than current UV detectors. Development of such APDs will enable enhanced detection and discrimination of biological and chemical compounds (e.g. nerve agents, explosives, or bacteria) using Raman spectroscopy. Within this project we will demonstrate an APD with extrinsic quantum efficiency exceeding 70%, high multiplication gain exceeding 106, and low dark current (<0.1nA). This will be achieved by harnessing our recent accomplishments in AlGaN growth as well as APD design, growth, and fabrication. At the end of our Phase II effort we will present a detector prototype that allows for real time detection of harmful bio or chemical species in the field that helps protect soldiers from exposure to such hazards. Results from this project will complement previous achievements from DARPA in the field of UV light sources (LUSTER) and find immediate application in the military and commercial sector.

The objective of this proposal is to develop an MOCVD growth process that will allow for the growth of thick, relaxed, doped and undoped, c-oriented AlGaN layers of any composition on the c-plane of native GaN and AlN substrates. Although these AlGaN layers will be relaxed, they will have a dislocation density similar to that of the used native substrates (103 - 105 cm-2). This will be achieved by growing AlGaN layers on GaN and AlN surfaces with pyramidal facets, allowing for the nucleation of misfit dislocations on a preferred slip system. The process will be combined with the misfit dislocation management to control threading dislocation density at the surface. Based on previous Phase I results, a clear path forward towards the realization of thick, relaxed AlGaN films with low dislocation densities on GaN and AlN single crystal substrates with up to 2������������������������������������ in diameter is presented. Using FACELO and by addressing the slip systems in the c-plane-grown AlGaN layers the technical goals will be realized and a 5 ��������m thick AlGaN film with any Al-content and low (<105 cm-2) dislocation densities will be possible.

The objective of this work is to develop a pathway for the realization of planar and embedded p-n junctions and high power devices based on these junctions, such as vertical JFETs and CAVETs. This objective is achieved by establishing selective area doping via ion implantation of Mg in GaN in combination with appropriate damage recovery and point defect control processes and by demonstrating GaN regrowth on p- and n-type GaN templates. At the end of this project, the understanding and control of selective area doping in GaN is applied to demonstrate arbitrarily placed, reliable, contactable, and generally useable p-n junction regions that meet or exceed the technical goals as defined in the FOA and enable high-performance and reliable vertical power electronic semiconductor devices.

The main objective is to interface biological entities, at the cellular level, with III-V semiconductors to enable manipulation of intracellular processes. Very unique and specific manipulation will be the goal of the proposed work via achieving control over interfacial assets (topography, chemistry, charge, stiffness) that can be triggered by the electronic properties of semiconductor materials. As a prototypical entity, the unicellular organism yeast will be used. A multidisciplinary team of biologists, surface materials chemists, and semiconductor growth researchers propose to develop a methodology to manipulate an individual yeast cell placed onto a working semiconductor device, establishing the biotronics paradigm as a complete manipulation loop between biological entity and electronics. This is realized by a response from the yeast that is triggered by external modulation of the interfacial electronic properties without applying external current when the biological entity and the electronic material surface are in contact. The strategy takes advantage of the induced persistent photoconductivity (PPC) by an external light source in the wide bandgap semiconductor. In this case, the external light source could be an integrated UV laser diode. PPC is due to the accumulation of charge carriers at the semiconductor surface/interface, thus it is a signature of the electronic modification of the semiconductor surface, Figure 1. In turn, the carriers promote the formation of reactive oxygen species on the surface. The presence of oxides, hydroxides and oxyhydroxides can trigger an information response from a biological entity. Interfacial changes can lead to molecular pathway changes that can result in manipulation of cell behavior via the activation/deactivation of targeted metabolic pathways. Subsequently, the information from the biological system will be transferred via the components of the semiconductor device. In general, the biotronics paradigm based on these processes can be represented as in Figure 2, where any possible manipulation of a healthy, functional cell is through ionic chemical pathways, that in turn, are accessed through electronic modulation of the semiconductors. Figure 3 shows a particular implementation of this paradigm. The basic process that relies on an appropriate interface between the yeast and the semiconductor will enable the localization of individual cells and subsequent manipulation of the intracellular processes inside each cell with high specificity with respect to individual cell organelles.

The United States military is deployed in more than 150 countries around the world, with approximately 170,000 of its active-duty personnel serving outside the United States and its territories. Many of the active duty personnel are stationed in developing countries where access to clean, potable water may be limited. In addition, many military operations rely on cooperation and integration with local partners, meaning that supplies, including water, needs to be provided by local sources. Minor contamination of water with bacteria (e.g., shigella, e.coli etc.) is often not a danger to the local community but can put the success of an ongoing operation at risk when military personnel has symptoms of bacterial gastroenteritis, resulting in lowered performance. Therefore, a fast and reliable disinfection method is sought after that can be used during operations on a daily bases without the need for resupply or maintenance. Therefore, light emitting diodes (LEDs), based on the III-nitride materials system (AlGaN), with emission in the UV have been proposed as a substitute. However, despite strong research efforts and interest, state-of-the-art UV-LEDs suffer from low power output and low overall efficiency. Based on previous results, it is proposed to have a prototype UV LED with output power >20mW with external quantum efficiency (EQE) exceeding 10% and wall plug efficiency (WPE) exceeding 5% at 265 nm by the end of Phase I, with the ultimate goal to reach EQE>30% and WPE>15% by employing the developed defect control schemes and reflective contacts in a possible Phase II. We will also study the feasibility of LEDs efficiently emitting at 219 nm. Details on our innovations and competitive edge that will drive next generation UVC diodes are discussed in the following sections. We expect EQE in the initial stages to be at least 15-20% at 265 nm, which is a fourfold increase over current technology at 265 nm. In general, we do not see major obstacles that prevent UV LEDs to perform on similar levels as VIS LEDs.

The proposal requests the purchase of a combined scannig probe and florescence microscopy system to image semiconductor/biointerfaces based on wide bandgap semicondouctors and individual microorganism cells. We propose to purchase the MFP-3D-BIO from Asylum Research, which is a high-performance scanning probe microscope designed specifically for biological applications. The MFP-3D is a versatile, modular design which combines the sub-molecular resolution imaging and precision force measurements of AFM with the broad range of optical microscopy techniques for simultaneous AFM and Brightfield, Phase Contrast, Fluorescence, etc. As part of the requested funds we will integrate the scanning probe microscope with a new inverted optical and florescence microscope from Olympus along with a camera and a set of objectives. The interfaces investigated by the PI and co-PI require time lapse imaging at multiple scales. The proposed microscope system is optimized for macro to micro imaging of cells, tissues, and small organisms, along with characterization of their mechanical properties. In addition, the system can perform state of the art characerization of the electronic component, the semiconductor interface, via variety of scanning modes such as lateral force microscopy, Kelvin probe and Force spectroscopy. The proposed instrument will enhance the data gathered through current Army Research Office funding and is essential for monitoring individual cell behavior in real time.

The objective of this proposal is to develop an MOCVD growth process that will allow for the growth of thick, relaxed, doped and undoped, c-oriented AlGaN layers of any composition on the c-plane of native GaN and AlN substrates. Although these AlGaN layers will be relaxed, they will have a dislocation density similar to that of the used native substrates (103 - 105 cm-2). This will be achieved by growing AlGaN layers on GaN and AlN surfaces with pyramidal facets, allowing for the nucleation of misfit dislocations on a preferred slip system. The process will be combined with the misfit dislocation management to control threading dislocation density at the surface.