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1. Bias-Insensitive GaAsSb/InP CC-MUTC Photodiodes for mmWave Generation up to 325 GHz

   https://doi.org/10.1109/JLT.2023.3298772  

   Morgan, Jesse S; Tabatabaei, Fatemehsadat; Fatema, Tasneem; Tang, Chak Wah; Sun, Keye; Lau, Kei May; Beling, Andreas (December 2023, Journal of Lightwave Technology)
2. GaAs/GaAsSb Core–Shell Configured Nanowire-Based Avalanche Photodiodes up to 1.3 μm Light Detection

   https://doi.org/10.1021/acsanm.2c03644  

   Pokharel, Rabin; Kuchoor, Hirandeep; Parakh, Mehul; Devkota, Shisir; Dawkins, Kendall; Ramaswamy, Priyanka; Li, Jia; Winkler, Christopher; Reynolds, Lew; Iyer, S. (April 2023, ACS Applied Nano Materials)

   We report the first study on a GaAs/GaAsSb core−shell (CS)-configured nanowire (NW)-based separate absorption, charge control, and multiplication region avalanche photodiode (APD) operating in the near-infrared (NIR) region. Heterostructure NWs consisted of GaAs and tunable band gap GaAs1−xSbx serving as the multiplication and absorption layers, respectively. A doping compensation of absorber material to boost material absorption, segment-wise annealing to suppress trap-assisted tunneling, and an intrinsic i-type and n-type combination of the hybrid axial core to suppress axial electric field are successfully adopted in this work to realize a room-temperature (RT) avalanche photodetection extending up to 1.3 μm. In an APD device operating at RT with a unity-gain responsivity of 0.2−0.25 A/W at ∼5 V, the peak gain of 160 @ 1064 nm and 18 V reverse bias, gain >50 @ 1.3 μm, are demonstrated. Thus, this work provides a foundation and prospects for exploiting greater freedom in NW photodiode design using hybrid axial and CS heterostructures. 

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3. Ensemble GaAsSb/GaAs axial configured nanowire-based separate absorption, charge, and multiplication avalanche near-infrared photodetectors

   https://doi.org/10.1039/D2NA00359G  

   Parakh, M.; Pokharel, R.; Dawkins, K.; Devkota, S.; Li, J.; Iyer, S. (January 2022, Nanoscale Advances)

   In this study, molecular beam epitaxially grown axially configured ensemble GaAsSb/GaAs separate absorption, charge, and multiplication (SACM) region-based nanowire avalanche photodetector device on non-patterned Si substrate is presented. Our device exhibits a low breakdown voltage ( V BR ) of ∼ −10 ± 2.5 V under dark, photocurrent gain ( M ) varying from 20 in linear mode to avalanche gain of 700 at V BR at a 1.064 μm wavelength. Positive temperature dependence of breakdown voltage ∼ 12.6 mV K −1 further affirms avalanche breakdown as the gain mechanism in our SACM NW APDs. Capacitance–voltage ( C – V ) and temperature-dependent noise characteristics also validated punch-through voltage ascertained from I – V measurements, and avalanche being the dominant gain mechanism in the APDs. The ensemble SACM NW APD device demonstrated a broad spectral room temperature response with a cut-off wavelength of ∼1.2 μm with a responsivity of ∼0.17–0.38 A W −1 at −3 V. This work offers a potential pathway toward realizing tunable nanowire-based avalanche photodetectors compatible with traditional Si technology. 

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4. A study of n-doping in self-catalyzed GaAsSb nanowires using GaTe dopant source and ensemble nanowire near-infrared photodetector

   https://doi.org/https://doi.org/10.1088/1361-6528/abb506  

   Devkota, Shisir; Parakh, Mehul; Johnson, Sean; Ramaswamy, Priyanka; Lowe, Michael; Penn, Aubrey; Reynolds, Lew; and Iyer, Shanthi (October 2020, Nanotechnology)

   null (Ed.)

   This work reports a comprehensive investigation of the effect of gallium telluride (GaTe) cell temperature variation (TGaTe) on the morphological, optical, and electrical properties of doped-GaAsSb nanowires (NWs) grown by Ga-assisted molecular beam epitaxy (MBE). These studies led to an optimum doping temperature of 550 °C for the growth of tellurium (Te)-doped GaAsSb NWs with the best optoelectronic and structural properties. Te incorporation resulted in a decrease in the aspect ratio of the NWs causing an increase in the Raman LO/TO vibrational mode intensity ratio, large PL emission with an exponential decay tail on the high energy side, promoting tunnel-assisted current conduction in ensemble NWs and significant photocurrent enhancement in the single nanowire. A Schottky barrier photodetector using Te-doped ensemble NWs with broad spectral range and a longer wavelength cutoff at ~ 1.2 µm was demonstrated. These photodetectors exhibited responsivity in the range of 580 – 620 A/W and detectivity of 1.2 – 3.8 × 1012 Jones. The doped GaAsSb NWs have the potential for further improvement, paving the path for high-performance near-infrared (NIR) photodetection applications. 

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5. A Study of Dopant Incorporation in Te - doped GaAsSb Nanowires using a Combination of XPS/UPS, and C-AFM/SKPM

   https://doi.org/https://doi.org/10.1038/s41598-021-87825-4  

   Ramaswamy, Priyanka; Devkota, Shisir; Pokharel, Rabin; Nalamati, Surya; Stevie, Fred; Jones, Keith; Reynolds, Lew; and Iyer, Shanthi. (April 2021, Scientific report)

   null (Ed.)

   We report the first study on doping assessment in Te-doped GaAsSb nanowires (NWs) with variation in Gallium Telluride (GaTe) cell temperature, using X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), conductive-atomic force microscopy (C-AFM), and scanning Kelvin probe microscopy (SKPM). The NWs were grown using Ga-assisted molecular beam epitaxy with a GaTe captive source as the dopant cell. Te-incorporation in the NWs was associated with a positive shift in the binding energy of the 3d shells of the core constituent elements in doped NWs in the XPS spectra, a lowering of the work function in doped NWs relative to undoped ones from UPS spectra, a significantly higher photoresponse in C-AFM and an increase in surface potential of doped NWs observed in SKPM relative to undoped ones. The carrier concentration of Te-doped GaAsSb NWs determined from UPS spectra are found to be consistent with the values obtained from simulated I-V characteristics. Thus, these surface analytical tools, XPS/UPS and C-AFM/SKPM, that do not require any sample preparation are found to be powerful characterization techniques to analyze the dopant incorporation and carrier density in homogeneously doped NWs. 

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