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Lab Capabilities and Selected Research Projects

Research_Summary_Figure
Research Overview and Lab Capabilities

​The Feezell lab has research interests in III-V optoelectronics for conventional and quantum applications, UV and visible integrated photonics, epitaxial growth using metal-organic chemical vapor deposition (MOCVD), optical and electrical device fabrication, semiconductor lasers (VCSELs, PCSELs, DFB/DBR, etc.), micro-LEDs, high-speed LEDs, bottom-up selective-area epitaxy, and carrier dynamics measurements. The lab contains a Veeco P-75 turbo-disc MOCVD system for epitaxial growth of III-nitride materials and associated device characterization systems. Also available at UNM are nanofabrication facilities, optical and structural characterization labs, and advanced RF testing equipment. Our group also works closely with the Center for Integrated Nanotechnologies (CINT) for access to spectroscopy labs and additional fabrication capabilities.

Vertical-Cavity Surface-Emitting Lasers (VCSELs)

Summary: Our research demonstrates the first optically pumped and electrically injected nonpolar m-plane GaN-based vertical-cavity surface-emitting lasers (VCSELs) utilizing lattice-matched nanoporous bottom distributed Bragg reflectors (DBRs). By employing selective electrochemical porosification, these high-index-contrast mirrors successfully bypass the severe growth time and structural defect constraints of conventional III-nitride reflectors to achieve a peak reflectance greater than 98% with only 15–16 pairs. Furthermore, leveraging the unique anisotropic material gain of the nonpolar crystal orientation produces inherently stable, single-mode emission that is strictly polarization-locked along the crystallographic a-direction.

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Key result:  First electrical injection of a nonpolar GaN VCSEL using nanoporous DBRs, achieving room-temperature pulsed lasing at 409 nm with 1.5 mW output power.

VCSELs
​References:  

  • S. Mishkat-Ul-Masabih, T. S. Luk, A. Rishinaramangalam, M. Monavarian, M. Nami, and D. Feezell, "Nanoporous distributed Bragg reflectors on free-standing nonpolar m-plane GaN," Appl. Phys. Lett., vol. 112, no. 4, p. 041109, Jan. 2018. https://doi.org.10.1063/1.5016083

  • S. M. Mishkat-Ul-Masabih, T. S. Luk, M. Monavarian, and D. F. Feezell, "Polarization-pinned emission of a continuous-wave optically pumped nonpolar GaN-based VCSEL using nanoporous distributed Bragg reflectors," Opt. Express, vol. 27, no. 7, pp. 9495–9501, Apr. 2019. https://doi.org/10.1364/OE.27.009495.

  • S. M. Mishkat-Ul-Masabih, A. A. Aragon, M. Monavarian, T. S. Luk, and D. F. Feezell, "Electrically injected nonpolar GaN-based VCSELs with lattice-matched nanoporous distributed Bragg reflector mirrors," Appl. Phys. Express, vol. 12, no. 3, p. 036504, Feb. 2019. https://doi.org/10.7567/1882-0786/ab0576.

High-Speed III-Nitrides (LEDs and SLDs)

Summary: Our research demonstrates that utilizing nonpolar and semipolar crystal orientations dramatically increases the modulation bandwidth of InGaN/GaN micro-LEDs and superluminescent diodes (SLDs) into the gigahertz range. By eliminating internal polarization fields, these micro-LED architectures optimize electron-hole wavefunction overlap for shorter carrier lifetimes, while a novel linearly tapered waveguide design pushes nonpolar SLD modulation speeds even further without reaching lasing threshold. Furthermore, integrating these high-speed crystal facets into bottom-up core-shell nanowire structures provides a cost-effective, scalable architecture for next-generation displays and visible-light communication.


Key result: Record modulation bandwidths for nonpolar and semipolar devices up to 1.5 GHz micro-LEDs and 2.5 GHz for SLDs.

High Speed III-Nitrides
​References:  

  • M. Monavarian, A. Rashidi, A. A. Aragon, S. H. Oh, A. K. Rishinaramangalam, S. P. DenBaars, and D. Feezell, "Impact of crystal orientation on the modulation bandwidth of InGaN/GaN light-emitting diodes," Appl. Phys. Lett., vol. 112, no. 4, p. 041104, Jan. 2018. https://doi.org/10.1063/1.5019730.

  • A. Rashidi, M. Monavarian, A. Aragon, A. Rishinaramangalam, and D. Feezell, "Nonpolar m-Plane InGaN/GaN Micro-Scale Light-Emitting Diode With 1.5 GHz Modulation Bandwidth," IEEE Electron Device Lett., vol. 39, no. 4, pp. 520–523, Apr. 2018. https://doi.org/10.1109/LED.2018.2803082.

  • M. Nami, A. Rashidi, M. Monavarian, S. Mishkat-Ul-Masabih, A. K. Rishinaramangalam, S. R. J. Brueck, and D. Feezell, "Electrically Injected GHz-Class GaN/InGaN Core–Shell Nanowire-Based μLEDs: Carrier Dynamics and Nanoscale Homogeneity," ACS Photonics, vol. 6, no. 7, pp. 1618–1625, Jul. 2019. https://doi.org/10.1021/acsphotonics.9b00639.

  • A. Rashidi , A. Rishinaramangalam, A. Aragon , S. Mishkat-Ul-Masabih , M. Monavarian , C. Lee, S. DenBaars, and D. Feezell, "High-speed nonpolar m-plane InGaN/GaN superluminescent diodes emitting at 450 nm," Appl. Phys. Lett., vol. 117, no. 23, p. 231103, Dec. 2020. https://doi.org/10.1109/LPT.2020.2976060.

LED Carrier Dynamics

Summary: Our research utilizes advanced small-signal electroluminescence (SSEL) to probe and numerically isolate the intrinsic and extrinsic carrier recombination dynamics in state-of-the-art, commercial-grade InGaN/GaN LEDs. By analyzing systematic wafer series, we map how carrier lifetimes scale across the "green gap" using blue, cyan, and green devices, evaluate extrinsic material limitations using green LEDs engineered with varied deep-level defect densities, and identify efficiency limitations associated with ultra-thin quantum wells. To overcome the classic limitation of standard SSEL models which assume an entirely homogeneous active region, we developed a mathematical Multiple-Carrier-Lifetime Model (MCLM). This framework successfully extracts effective recombination lifetimes, allowing us to accurately quantify carrier dynamics in complex, dual-color, and V-pit engineered multiple-quantum-well (MQW) architectures displaying heavily non-uniform internal carrier distributions.

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Key result: Isolation of recombination rates confirming that intrinsic Auger–Meitner processes—rather than defect-related trap-assisted pathways—drive high-power efficiency droop across all studied wavelengths, thicknesses, and defect profiles.

Carrier Dynamics
​References:  

  • X. Li, N. Pant, E. DeJong, A. T. Elshafiey, R. Armitage, E. Kioupakis, and D. Feezell, "Carrier dynamics in blue, cyan, and green InGaN/GaN LEDs measured by small-signal electroluminescence," Appl. Phys. Lett., vol. 122, no. 21, p. 212108, May 2023. https://doi.org/10.1063/5.0151301.

  • X. Li, E. DeJong, R. Armitage, A. M. Armstrong, and D. Feezell, "Influence of trap-assisted and intrinsic Auger–Meitner recombination on efficiency droop in green InGaN/GaN LEDs," Appl. Phys. Lett., vol. 123, no. 11, p. 112109, Sep. 2023. https://doi.org/10.1063/5.0167430.

  • X. Li, E. DeJong, R. Armitage, and D. Feezell, "Multiple-carrier-lifetime model for carrier dynamics in InGaN/GaN LEDs with a non-uniform carrier distribution," J. Appl. Phys., vol. 135, no. 3, p. 035702, Jan. 2024. https://doi.org/10.1063/5.0184456.

  • X. Li, N. Pant, S. I. Rahman, R. Armitage, S. Rajan, E. Kioupakis, and D. Feezell, "Impact of quantum well thickness on efficiency loss in InGaN/GaN LEDs: Challenges for thin-well designs," Appl. Phys. Lett., vol. 126, no. 13, p. 132102, Mar. 2025. https://doi.org/10.1063/5.0258108.

  • X. Li, R. Armitage, and D. Feezell, "Spectral and small-signal electroluminescence analysis of carrier dynamics in dual-color InGaN/GaN light-emitting diodes," J. Appl. Phys., vol. 140, no. 10, p. 105702, Sep. 2026. https://doi.org/10.1063/5.0334803.

Nanostructure Growth and Devices

Summary: Our research utilizes catalyst-free, bottom-up selective-area epitaxy (SAE) via metal-organic chemical vapor deposition (MOCVD) to synthesize highly uniform GaN/InGaN core–shell nanowires and semipolar triangular-stripe architectures directly on economical sapphire substrates. By engineering the mask pitch to tune emission across the blue-to-green spectrum and introducing an n-AlGaN underlayer to suppress growth-mask impurity diffusion, we eliminate diode reverse-leakage to realize high-performance electrically injected nanostripe LEDs and nanowire devices with internal quantum efficiency of 62%. Furthermore, leveraging stable semipolar crystal facets that naturally terminate into an atomically sharp apex under 1 nm, we demonstrate that these mechanically resilient nanowires can be integrated into advanced scanning systems to achieve sub-10-nm resolution field-emission probe nanolithography.

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Key result: Monolithic visible wavelength tuning up to 520 nm combined with successful electrical injection of nanostripe LEDs achieving a 62% internal quantum efficiency and sub-10-nm ambient probe lithography resolution.

Nanostructures
​References:  

  • A. K. Rishinaramangalam, M. Nami, M. N. Fairchild, D. M. Shima, G. Balakrishnan, S. R. J. Brueck, and D. F. Feezell, "Semipolar InGaN/GaN nanostructure light-emitting diodes on c-plane sapphire," Appl. Phys. Express, vol. 9, no. 3, p. 032101, Feb. 2016. https://doi.org/10.7567/APEX.9.032101.

  • M. Nami, R. F. Eller, S. Okur, A. K. Rishinaramangalam, S. Liu, I. Brener, and D. F. Feezell, "Tailoring the morphology and luminescence of GaN/InGaN core–shell nanowires using bottom-up selective-area epitaxy," Nanotechnology, vol. 28, no. 2, p. 025202, Jan. 2017. https://doi.org/10.1088/0957-4484/28/2/025202.

  • A. K. Rishinaramangalam, M. Nami, D. M. Shima, G. Balakrishnan, S. R. J. Brueck, and D. F. Feezell, "Reduction of reverse-leakage current in selective-area-grown GaN-based core–shell nanostructure LEDs using AlGaN layers," Phys. Status Solidi A, vol. 214, no. 4, p. 1600776, Apr. 2017. https://doi.org/10.1002/pssa.201600776.

  • M. Nami, I. E. Stricklin, K. M. DaVico, S. Mishkat-Ul-Masabih, A. K. Rishinaramangalam, S. R. J. Brueck, I. Brener, and D. F. Feezell, "Carrier Dynamics and Electro-Optical Characterization of High-Performance GaN/InGaN Core-Shell Nanowire Light-Emitting Diodes," Sci. Rep., vol. 8, no. 1, p. 501, Jan. 2018. https://doi.org/10.1038/s41598-017-18833-6.

  • S. Okur, A. K. Rishinaramangalam, S. Mishkat-Ul-Masabih, M. Nami, S. Liu, I. Brener, S. R. J. Brueck, and D. F. Feezell, "Spectrally-resolved internal quantum efficiency and carrier dynamics of semipolar (1011) core-shell triangular nanostripe GaN/InGaN LEDs," Nanotechnology, vol. 29, no. 23, p. 235206, Jun. 2018. https://doi.org/10.1088/1361-6528/aab82e.

  • M. Behzadirad, S. Mecholdt, J. N. Randall, J. B. Ballard, J. Owen, A. K. Rishinaramangalam, A. Reum, T. Gotszalk, D. F. Feezell, I. W. Rangelow, and T. Busani, "Advanced Scanning Probe Nanolithography Using GaN Nanowires," Nano Lett., vol. 21, no. 17, pp. 7195–7201, Aug. 2021. https://doi.org/10.1021/acs.nanolett.1c00127.

Electronic Devices and Radiation Effects

Summary:  Our research investigates the optimization of high-voltage vertical GaN power switches and evaluates their long-term reliability and tolerance under harsh, radiation-heavy environments. By fabricating regrown nonpolar m-plane vertical p-n and Schottky diodes, we systematically characterize how silicon, oxygen, and carbon interfacial impurities alter forward and reverse performance, and we successfully demonstrate post-etch wet chemical and photoelectrochemical (PEC) treatments that suppress dry-etch-induced midgap defect states. Furthermore, testing these devices under extreme high-dose gamma-ray and fast/thermal neutron exposures reveals distinct, crystal-orientation-dependent degradation and recovery dynamics between Ga-polar and N-polar architectures, driven by the unique interplay of surface stoichiometry, native point vacancies, and radiation-induced acceptor activation.
 

Key result: Realization of regrown nonpolar vertical diodes supporting large electric fields up to 3.35 MV/cm with a 540 V breakdown voltage, alongside the discovery that N-polar diodes demonstrate superior reverse-bias radiation tolerance to fast neutrons compared to Ga-polar devices.

Electronic Devices and Radiation Effects
​References:  

  • M. Monavarian, G. Pickrell, A. A. Aragon, I. Stricklin, M. H. Crawford, A. A. Allerman, K. C. Celio, F. Léonard, A. A. Talin, A. M. Armstrong, and D. Feezell, "High-Voltage Regrown Nonpolar m-Plane Vertical p-n Diodes: A Step Toward Future Selective-Area-Doped Power Switches," IEEE Electron Device Lett., vol. 40, no. 3, pp. 387–390, Mar. 2019. https://doi.org/10.1109/LED.2019.2892345.

  • A. Aragon, M. Monavarian, I. Stricklin, G. Pickrell, Mary Crawford, A. Allerman, A. M. Armstrong, and D. Feezell, "Interfacial Impurities and Their Electronic Signatures in High-Voltage Regrown Nonpolar m-Plane GaN Vertical p–n Diodes," Phys. Status Solidi A, vol. 216, no. 23, p. 1900757, Dec. 2019. https://doi.org/10.1002/pssa.201900757.

  • A. Aragon, M. Monavarian, G. Pickrell, M. Crawford, A. Allerman, D. Feezell, and A. M. Armstrong, "Defect suppression in wet-treated etched-and-regrown nonpolar m-plane GaN vertical Schottky diodes: A deep-level optical spectroscopy analysis," J. Appl. Phys., vol. 128, no. 18, p. 185703, Nov. 2020. https://doi.org/10.1063/5.0018829.

  • F. Mirkhosravi, A. Rashidi, J. Gallagher, M. Monavarian, A. Aragon, K. Ahn, Y. K. Ooi, A. Lintereur, E. K. Mace, M. A. Scarpulla, and D. Feezell, "Impact of high-dose gamma-ray irradiation on electrical characteristics of N-polar and Ga-polar GaN p–n diodes," AIP Advances, vol. 11, no. 2, p. 025009, Feb. 2021. https://doi.org/10.1063/5.0021382.

  • F. Mirkhosravi, A. Rashidi, A. T. Elshafiey, J. Gallagher, Z. Abedi, K. Ahn, A. Lintereur, E. K. Mace, M. A. Scarpulla, and D. Feezell, "Effects of fast and thermal neutron irradiation on Ga-polar and N-polar GaN diodes," J. Appl. Phys., vol. 133, no. 1, p. 015704, Jan. 2023. https://doi.org/10.1063/5.0119294.

© 2026 Daniel Feezell

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