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Creators/Authors contains: "Ghosh, Arnob"

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  1. Abstract

    This paper presents the design, material growth and fabrication of AlGaN laser structures grown by plasma-assisted molecular beam epitaxy. Considering hole transport to be the major challenge, our ultraviolet-A diode laser structures have a compositionally graded transparent tunnel junction, resulting in superior hole injection and a low contact resistance. By optimizing active region thickness, a five-fold improvement in photoluminescence intensity is obtained compared to that of our own non-optimized test structures. The electrical and optical characteristics of processed devices demonstrate only spontaneous emission with a peak wavelength at 354 nm. The devices operate up to a continuous-wave current density of 11.1 kA cm−2at room temperature, which is the highest reported for laser structures grown on AlGaN templates. Additionally, they exhibit a record-low voltage drop of 8.5 V to achieve this current density.

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  2. Abstract In this work, we demonstrate two-junction UV LEDs enabled by transparent tunnel junctions. Low voltage-drop tunnel junctions were realized in Al 0.3 Ga 0.7 N layers through a combination of high doping and compositional grading. Capacitance and current–voltage measurements confirmed the operation of two junctions in series. The voltage drop of the two-junction LED was 2.1 times that of an equivalent single-junction LED, and the two-junction LED had higher external quantum efficiency (147%) than the single junction. 
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    Free, publicly-accessible full text available August 1, 2024
  3. Free, publicly-accessible full text available June 7, 2024
  4. Ultra-violet (UV) light emitting diodes operating at 339 nm using transparent interband tunnel junctions are reported. Tunneling-based ultraviolet light emitting diodes were grown by plasma-assisted molecular beam epitaxy on 30% Al-content AlGaN layers. A low tunnel junction voltage drop is obtained through the use of compositionally graded n and p-type layers in the tunnel junction, which enhance hole density and tunneling rates. The transparent tunnel junction-based UV LED reported here show a low voltage drop of 5.55 V at 20 A/cm2 and an on-wafer external quantum efficiency of 1.02% at 80 A/cm2. 
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    Free, publicly-accessible full text available February 20, 2024
  5. The recent framework for spectrum sharing in the 3.5 GHz band allows for Environment Sensing Capability operators (ESCs) to measure spectrum occupancy so as to enable commercial use of this spectrum when federal incumbent users are not present. Each ESC will contract with one or more Spectrum Access Systems (SASs) to provide spectrum occupancy data. Commercial firms using the band will in turn contract with a SAS to determine when it can access the spectrum. Initially, the decisions of which ESC and SAS to partner with will likely be based on long-term contracts. In this paper, we consider an alternative framework, in which an ESC sells its spectrum management information via a spot market so that from periodto- period a commercial user can select a different ESC from which to acquire spectrum measurements. We develop a game theoretic model to analyze such a market and show that using such a spot market may better enable multiple commercial firms to operate in a given spectrum band. We also show that this increased competition may not benefit consumer surplus unless firms adopt a non-stationary strategy profile. 
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  6. The recent framework for tiered spectrum sharing in the 3.5 GHz band establishes rules in which multiple firms called Environment Sensing Capability operators (ESCs) may measure spectrum occupancy and sell these measurements to other firms to help facilitate spectrum access. Motived by this we consider a scenario in which two spectrum access firms (SAs) seeks to access a shared band of spectrum and must in turn purchase spectrum measurements from one of two ESCs. Given the measurements they purchase, the SA firms then compete on price to serve customers in a shared band of spectrum. We study how differences in the quality and price of the spectrum measurements impact the resulting market equilibrium between the SAs and find that having different qualities of measurements available to different SAs can lead to better economic welfare. 
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