The Experts below are selected from a list of 1983 Experts worldwide ranked by ideXlab platform

Manijeh Razeghi - One of the best experts on this subject based on the ideXlab platform.

  • reliability in room temperature negative differential resistance characteristics of low aluminum content algan gan double barrier Resonant Tunneling Diodes
    2010
    Co-Authors: Can Bayram, Z Vashaei, Manijeh Razeghi
    Abstract:

    AlGaN/GaN Resonant Tunneling Diodes (RTDs), consisting of 20% (10%) aluminum-content in double-barrier (DB) active layer, were grown by metal-organic chemical vapor deposition on freestanding polar (c-plane) and nonpolar (m-plane) GaN substrates. RTDs were fabricated into 35-μm-diameter devices for electrical characterization. Lower aluminum content in the DB active layer and minimization of dislocations and polarization fields increased the reliability and reproducibility of room-temperature negative differential resistance (NDR). Polar RTDs showed decaying NDR behavior, whereas nonpolar ones did not significantly. Averaging over 50 measurements, nonpolar RTDs demonstrated a NDR of 67 Ω, a current-peak-to-valley ratio of 1.08, and an average oscillator output power of 0.52 mW.

  • room temperature negative differential resistance characteristics of polar iii nitride Resonant Tunneling Diodes
    2010
    Co-Authors: Can Bayram, Z Vashaei, Manijeh Razeghi
    Abstract:

    III-nitride Resonant Tunneling Diodes (RTDs), consisting Al0.2Ga0.8N/GaN double-barrier (DB) active layers, were grown on c-plane lateral epitaxial overgrowth (LEO) GaN/sapphire and c-plane freestanding (FS) GaN. RTDs on both templates, fabricated into mesa diameters ranging from 5 to 35 μm, showed negative differential resistance (NDR) at room temperature. NDR characteristics (voltage and current density at NDR onset and current-peak-to-valley ratio) were analyzed and reported as a function of device size and substrate choice. Our results show that LEO RTDs perform as well as FS ones and DB active layer design and quality have been the bottlenecks in III-nitride RTDs.

  • demonstration of negative differential resistance in gan aln Resonant Tunneling Diodes at room temperature
    2010
    Co-Authors: Z Vashaei, Can Bayram, Manijeh Razeghi
    Abstract:

    GaN/AlN Resonant Tunneling Diodes (RTD) were grown by metal-organic chemical vapor deposition (MOCVD) and negative differential resistance with peak-to-valley ratios as high as 2.15 at room temperature was demonstrated. Effect of material quality on RTDs’ performance was investigated by growing RTD structures on AlN, GaN, and lateral epitaxial overgrowth GaN templates. Our results reveal that negative differential resistance characteristics of RTDs are very sensitive to material quality (such as surface roughness) and MOCVD is a suitable technique for III-nitride-based quantum devices.

  • aln gan double barrier Resonant Tunneling Diodes grown by metal organic chemical vapor deposition
    2010
    Co-Authors: Can Bayram, Z Vashaei, Manijeh Razeghi
    Abstract:

    AlN/GaN double-barrier Resonant Tunneling Diodes (RTDs) were grown by metal-organic chemical vapor deposition on sapphire. RTDs were fabricated via standard processing steps. RTDs demonstrate a clear negative differential resistance (NDR) at room temperature (RT). The NDR was observed around 4.7 V with a peak current density of 59 kA/cm2 and a peak-to-valley ratio of 1.6 at RT. Dislocation-free material is shown to be the key for the performance of GaN RTDs.

E R Brown - One of the best experts on this subject based on the ideXlab platform.

  • superior growth yield repeatability and switching performance in gan based Resonant Tunneling Diodes
    2020
    Co-Authors: Tyler A Growden, E R Brown, D F Storm, Weidong Zhang, Evan M Cornuelle, Brian P Downey, J A Roussos, Nicholas Cronk, Laura B Ruppalt, James G Champlain
    Abstract:

    We report the direct measurement of record fast switching speeds in GaN/AlN Resonant Tunneling Diodes (RTDs). The devices, grown by plasma-assisted molecular-beam epitaxy, displayed three repeatable negative differential resistance (NDR) regions below a bias of +6 V. A room temperature peak-to-valley current ratio (PVCR) > 2 was observed, which represents a marked improvement over recent reports. Measurements carried out on hundreds of devices, of varying sizes, revealed a yield of ∼90%. Repeatability measurements consisting of 3000 sweeps resulted in a standard deviation, relative to the mean, of < 0.1%. Temperature dependent measurements combined with non-equilibrium Green's function based quantum transport simulations suggest the presence of both three-dimensional (3D) and two-dimensional (2D) emitters, giving rise to three NDR regions. Finally, a valley current density vs perimeter-to-area-ratio study indicates the presence of a surface leakage current mechanism, which reduces the PVCR.

  • investigation of switching time in gan aln Resonant Tunneling Diodes by experiments and p spice models
    2020
    Co-Authors: Wd Zhang, Tyler A Growden, Paul R Berger, D F Storm, David J Meyer, E R Brown
    Abstract:

    The experimental and simulated switching behavior across the negative differential resistance (NDR) region of GaN/AlN double-barrier Resonant Tunneling Diodes (RTDs) is presented. The shortest 10%–90% experimental switching time was ~55 ps. The experimental results are also studied with P-SPICE circuit models, which show that the relatively low peak-to-valley current ratio (~1.5), relatively high specific contact resistance ( $\geq \textsf {1}\times \textsf {10}^{-\textsf {6}}\,\,\Omega $ -cm2), and relatively large specific capacitance limit the switching time.

  • fabrication and characterization of gan aln Resonant Tunneling Diodes
    2020
    Co-Authors: Wd Zhang, E R Brown, Tyler A Growden, Paul R Berger, D F Storm, David J Meyer
    Abstract:

    This chapter reviews our recent efforts on growth, fabrication, and characterization of GaN/AlN Resonant Tunneling Diodes (RTDs). Working GaN/AlN RTDs were successfully demonstrated, and they could function well under the flux of very high current densities (e.g., ∼431 kA/cm2) without thermal breakdown. The high-speed nature of these devices was confirmed through switching experiments, achieving a 10–90% switching time of ≈55 ps. A fmax calculation shows a small-signal oscillation with frequency up to 164 GHz is possible. Unlike InGaAs/AlAs RTDs, the peak-to-valley current ratios (PVCRs) of GaN/AlN RTDs remain ∼1.5. Through computer modeling, temperature measurements, and material diagnosis, we reveal that there could be stronger inelastic scattering processes contributing to the valley current other than the coherent Tunneling in the GaN/AlN RTDs. The possible inelastic mechanisms include optical phonons, interface roughness, and dislocations. Thus, the growth of high-quality GaN/AlN heterostructures and the evolution of bulk GaN substrates are critical for getting better performance devices. Finally, unipolar electroluminescence, without the presence of p-type doping, was observed in GaN/AlN RTDs. The interband Tunneling process, which generates holes for the optical recombination, is likely due to the strong electric fields originating from the polarization effects native to wurtzite heterostructures.

  • 930 ka cm 2 peak Tunneling current density in gan aln Resonant Tunneling Diodes grown on mocvd gan on sapphire template
    2019
    Co-Authors: Tyler A Growden, E R Brown, D F Storm, David J Meyer, Weidong Zhang, Evan M Cornuelle, Logan M Whitaker, Jeffrey W Daulton, R J Molnar, Paul R Berger
    Abstract:

    We report on the design and fabrication of ultrahigh current density GaN/AlN double barrier Resonant Tunneling Diodes grown via rf-plasma assisted molecular-beam epitaxy. The device structure was grown on a metal-organic chemical vapor deposition GaN-on-sapphire template. The devices displayed repeatable room temperature negative differential resistance with peak Tunneling current densities (Jp) between 637 and 930 kA/cm2. Analysis of temperature dependent measurements revealed the presence of severe self-heating effects, which allow strong phonon scattering that deteriorates the electron quantum transport. Finally, a qualitative comparison to the same structure grown on a low dislocation density freestanding GaN substrate has shown that sapphire-based templates are a feasible alternative.We report on the design and fabrication of ultrahigh current density GaN/AlN double barrier Resonant Tunneling Diodes grown via rf-plasma assisted molecular-beam epitaxy. The device structure was grown on a metal-organic chemical vapor deposition GaN-on-sapphire template. The devices displayed repeatable room temperature negative differential resistance with peak Tunneling current densities (Jp) between 637 and 930 kA/cm2. Analysis of temperature dependent measurements revealed the presence of severe self-heating effects, which allow strong phonon scattering that deteriorates the electron quantum transport. Finally, a qualitative comparison to the same structure grown on a low dislocation density freestanding GaN substrate has shown that sapphire-based templates are a feasible alternative.

  • 431 ka cm 2 peak Tunneling current density in gan aln Resonant Tunneling Diodes
    2018
    Co-Authors: Tyler A Growden, E R Brown, D F Storm, David J Meyer, Weidong Zhang, Katurah Hansen, Parastou Fakhimi, Paul R Berger
    Abstract:

    We report on the design and fabrication of high current density GaN/AlN double barrier Resonant Tunneling Diodes grown via plasma assisted molecular-beam epitaxy on bulk GaN substrates. A quantum-transport solver was used to model and optimize designs with high levels of doping and ultra-thin AlN barriers. The devices displayed repeatable room temperature negative differential resistance with peak-to-valley current ratios ranging from 1.20 to 1.60. A maximum peak Tunneling current density (Jp) of 431 kA/cm2 was observed. Cross-gap near-UV (370–385 nm) electroluminescence (EL) was observed above +6 V when holes, generated from a polarization induced Zener Tunneling effect, recombine with electrons in the emitter region. Analysis of temperature dependent measurements, thermal resistance, and the measured EL spectra revealed the presence of severe self-heating effects.

Paul R Berger - One of the best experts on this subject based on the ideXlab platform.

  • investigation of switching time in gan aln Resonant Tunneling Diodes by experiments and p spice models
    2020
    Co-Authors: Wd Zhang, Tyler A Growden, Paul R Berger, D F Storm, David J Meyer, E R Brown
    Abstract:

    The experimental and simulated switching behavior across the negative differential resistance (NDR) region of GaN/AlN double-barrier Resonant Tunneling Diodes (RTDs) is presented. The shortest 10%–90% experimental switching time was ~55 ps. The experimental results are also studied with P-SPICE circuit models, which show that the relatively low peak-to-valley current ratio (~1.5), relatively high specific contact resistance ( $\geq \textsf {1}\times \textsf {10}^{-\textsf {6}}\,\,\Omega $ -cm2), and relatively large specific capacitance limit the switching time.

  • fabrication and characterization of gan aln Resonant Tunneling Diodes
    2020
    Co-Authors: Wd Zhang, E R Brown, Tyler A Growden, Paul R Berger, D F Storm, David J Meyer
    Abstract:

    This chapter reviews our recent efforts on growth, fabrication, and characterization of GaN/AlN Resonant Tunneling Diodes (RTDs). Working GaN/AlN RTDs were successfully demonstrated, and they could function well under the flux of very high current densities (e.g., ∼431 kA/cm2) without thermal breakdown. The high-speed nature of these devices was confirmed through switching experiments, achieving a 10–90% switching time of ≈55 ps. A fmax calculation shows a small-signal oscillation with frequency up to 164 GHz is possible. Unlike InGaAs/AlAs RTDs, the peak-to-valley current ratios (PVCRs) of GaN/AlN RTDs remain ∼1.5. Through computer modeling, temperature measurements, and material diagnosis, we reveal that there could be stronger inelastic scattering processes contributing to the valley current other than the coherent Tunneling in the GaN/AlN RTDs. The possible inelastic mechanisms include optical phonons, interface roughness, and dislocations. Thus, the growth of high-quality GaN/AlN heterostructures and the evolution of bulk GaN substrates are critical for getting better performance devices. Finally, unipolar electroluminescence, without the presence of p-type doping, was observed in GaN/AlN RTDs. The interband Tunneling process, which generates holes for the optical recombination, is likely due to the strong electric fields originating from the polarization effects native to wurtzite heterostructures.

  • 930 ka cm 2 peak Tunneling current density in gan aln Resonant Tunneling Diodes grown on mocvd gan on sapphire template
    2019
    Co-Authors: Tyler A Growden, E R Brown, D F Storm, David J Meyer, Weidong Zhang, Evan M Cornuelle, Logan M Whitaker, Jeffrey W Daulton, R J Molnar, Paul R Berger
    Abstract:

    We report on the design and fabrication of ultrahigh current density GaN/AlN double barrier Resonant Tunneling Diodes grown via rf-plasma assisted molecular-beam epitaxy. The device structure was grown on a metal-organic chemical vapor deposition GaN-on-sapphire template. The devices displayed repeatable room temperature negative differential resistance with peak Tunneling current densities (Jp) between 637 and 930 kA/cm2. Analysis of temperature dependent measurements revealed the presence of severe self-heating effects, which allow strong phonon scattering that deteriorates the electron quantum transport. Finally, a qualitative comparison to the same structure grown on a low dislocation density freestanding GaN substrate has shown that sapphire-based templates are a feasible alternative.We report on the design and fabrication of ultrahigh current density GaN/AlN double barrier Resonant Tunneling Diodes grown via rf-plasma assisted molecular-beam epitaxy. The device structure was grown on a metal-organic chemical vapor deposition GaN-on-sapphire template. The devices displayed repeatable room temperature negative differential resistance with peak Tunneling current densities (Jp) between 637 and 930 kA/cm2. Analysis of temperature dependent measurements revealed the presence of severe self-heating effects, which allow strong phonon scattering that deteriorates the electron quantum transport. Finally, a qualitative comparison to the same structure grown on a low dislocation density freestanding GaN substrate has shown that sapphire-based templates are a feasible alternative.

  • 431 ka cm 2 peak Tunneling current density in gan aln Resonant Tunneling Diodes
    2018
    Co-Authors: Tyler A Growden, E R Brown, D F Storm, David J Meyer, Weidong Zhang, Katurah Hansen, Parastou Fakhimi, Paul R Berger
    Abstract:

    We report on the design and fabrication of high current density GaN/AlN double barrier Resonant Tunneling Diodes grown via plasma assisted molecular-beam epitaxy on bulk GaN substrates. A quantum-transport solver was used to model and optimize designs with high levels of doping and ultra-thin AlN barriers. The devices displayed repeatable room temperature negative differential resistance with peak-to-valley current ratios ranging from 1.20 to 1.60. A maximum peak Tunneling current density (Jp) of 431 kA/cm2 was observed. Cross-gap near-UV (370–385 nm) electroluminescence (EL) was observed above +6 V when holes, generated from a polarization induced Zener Tunneling effect, recombine with electrons in the emitter region. Analysis of temperature dependent measurements, thermal resistance, and the measured EL spectra revealed the presence of severe self-heating effects.

  • a nonlinear circuit simulation of switching process in Resonant Tunneling Diodes
    2016
    Co-Authors: Wd Zhang, E R Brown, Tyler A Growden, Paul R Berger, R Droopad
    Abstract:

    A large-signal circuit model is used to compute the switching time for double-barrier Resonant-Tunneling Diodes. The model consists of linear circuit elements plus a nonlinear $I$ – $V$ characteristic. The linear elements include a series resistor, a capacitor, and an inductor. The capacitance considers the charge accumulation, depletion in spacer layers, as well as charging-discharging of the quantum-well (QW) region. The inductance accounts for the delay of the current with respect to the voltage across the QW during the abrupt switching transition through the negative differential resistance region. A second-order Runge–Kutta method is used to solve for the switching transient, and then fit to experimental data for a high-quality InGaAs/AlAs Resonant Tunneling diode (RTD) using the QW inductance as a fitting parameter. Excellent agreement is found for the 10%–90% switching time with a calculated capacitance of 98 fF and a fitted inductance of 1300 pH. This large-signal inductance is approximately $7\times $ greater than the small-signal inductance that has been successfully used to predict the fmax of RTDs such as the one tested here.

Tyler A Growden - One of the best experts on this subject based on the ideXlab platform.

  • superior growth yield repeatability and switching performance in gan based Resonant Tunneling Diodes
    2020
    Co-Authors: Tyler A Growden, E R Brown, D F Storm, Weidong Zhang, Evan M Cornuelle, Brian P Downey, J A Roussos, Nicholas Cronk, Laura B Ruppalt, James G Champlain
    Abstract:

    We report the direct measurement of record fast switching speeds in GaN/AlN Resonant Tunneling Diodes (RTDs). The devices, grown by plasma-assisted molecular-beam epitaxy, displayed three repeatable negative differential resistance (NDR) regions below a bias of +6 V. A room temperature peak-to-valley current ratio (PVCR) > 2 was observed, which represents a marked improvement over recent reports. Measurements carried out on hundreds of devices, of varying sizes, revealed a yield of ∼90%. Repeatability measurements consisting of 3000 sweeps resulted in a standard deviation, relative to the mean, of < 0.1%. Temperature dependent measurements combined with non-equilibrium Green's function based quantum transport simulations suggest the presence of both three-dimensional (3D) and two-dimensional (2D) emitters, giving rise to three NDR regions. Finally, a valley current density vs perimeter-to-area-ratio study indicates the presence of a surface leakage current mechanism, which reduces the PVCR.

  • investigation of switching time in gan aln Resonant Tunneling Diodes by experiments and p spice models
    2020
    Co-Authors: Wd Zhang, Tyler A Growden, Paul R Berger, D F Storm, David J Meyer, E R Brown
    Abstract:

    The experimental and simulated switching behavior across the negative differential resistance (NDR) region of GaN/AlN double-barrier Resonant Tunneling Diodes (RTDs) is presented. The shortest 10%–90% experimental switching time was ~55 ps. The experimental results are also studied with P-SPICE circuit models, which show that the relatively low peak-to-valley current ratio (~1.5), relatively high specific contact resistance ( $\geq \textsf {1}\times \textsf {10}^{-\textsf {6}}\,\,\Omega $ -cm2), and relatively large specific capacitance limit the switching time.

  • fabrication and characterization of gan aln Resonant Tunneling Diodes
    2020
    Co-Authors: Wd Zhang, E R Brown, Tyler A Growden, Paul R Berger, D F Storm, David J Meyer
    Abstract:

    This chapter reviews our recent efforts on growth, fabrication, and characterization of GaN/AlN Resonant Tunneling Diodes (RTDs). Working GaN/AlN RTDs were successfully demonstrated, and they could function well under the flux of very high current densities (e.g., ∼431 kA/cm2) without thermal breakdown. The high-speed nature of these devices was confirmed through switching experiments, achieving a 10–90% switching time of ≈55 ps. A fmax calculation shows a small-signal oscillation with frequency up to 164 GHz is possible. Unlike InGaAs/AlAs RTDs, the peak-to-valley current ratios (PVCRs) of GaN/AlN RTDs remain ∼1.5. Through computer modeling, temperature measurements, and material diagnosis, we reveal that there could be stronger inelastic scattering processes contributing to the valley current other than the coherent Tunneling in the GaN/AlN RTDs. The possible inelastic mechanisms include optical phonons, interface roughness, and dislocations. Thus, the growth of high-quality GaN/AlN heterostructures and the evolution of bulk GaN substrates are critical for getting better performance devices. Finally, unipolar electroluminescence, without the presence of p-type doping, was observed in GaN/AlN RTDs. The interband Tunneling process, which generates holes for the optical recombination, is likely due to the strong electric fields originating from the polarization effects native to wurtzite heterostructures.

  • 930 ka cm 2 peak Tunneling current density in gan aln Resonant Tunneling Diodes grown on mocvd gan on sapphire template
    2019
    Co-Authors: Tyler A Growden, E R Brown, D F Storm, David J Meyer, Weidong Zhang, Evan M Cornuelle, Logan M Whitaker, Jeffrey W Daulton, R J Molnar, Paul R Berger
    Abstract:

    We report on the design and fabrication of ultrahigh current density GaN/AlN double barrier Resonant Tunneling Diodes grown via rf-plasma assisted molecular-beam epitaxy. The device structure was grown on a metal-organic chemical vapor deposition GaN-on-sapphire template. The devices displayed repeatable room temperature negative differential resistance with peak Tunneling current densities (Jp) between 637 and 930 kA/cm2. Analysis of temperature dependent measurements revealed the presence of severe self-heating effects, which allow strong phonon scattering that deteriorates the electron quantum transport. Finally, a qualitative comparison to the same structure grown on a low dislocation density freestanding GaN substrate has shown that sapphire-based templates are a feasible alternative.We report on the design and fabrication of ultrahigh current density GaN/AlN double barrier Resonant Tunneling Diodes grown via rf-plasma assisted molecular-beam epitaxy. The device structure was grown on a metal-organic chemical vapor deposition GaN-on-sapphire template. The devices displayed repeatable room temperature negative differential resistance with peak Tunneling current densities (Jp) between 637 and 930 kA/cm2. Analysis of temperature dependent measurements revealed the presence of severe self-heating effects, which allow strong phonon scattering that deteriorates the electron quantum transport. Finally, a qualitative comparison to the same structure grown on a low dislocation density freestanding GaN substrate has shown that sapphire-based templates are a feasible alternative.

  • 431 ka cm 2 peak Tunneling current density in gan aln Resonant Tunneling Diodes
    2018
    Co-Authors: Tyler A Growden, E R Brown, D F Storm, David J Meyer, Weidong Zhang, Katurah Hansen, Parastou Fakhimi, Paul R Berger
    Abstract:

    We report on the design and fabrication of high current density GaN/AlN double barrier Resonant Tunneling Diodes grown via plasma assisted molecular-beam epitaxy on bulk GaN substrates. A quantum-transport solver was used to model and optimize designs with high levels of doping and ultra-thin AlN barriers. The devices displayed repeatable room temperature negative differential resistance with peak-to-valley current ratios ranging from 1.20 to 1.60. A maximum peak Tunneling current density (Jp) of 431 kA/cm2 was observed. Cross-gap near-UV (370–385 nm) electroluminescence (EL) was observed above +6 V when holes, generated from a polarization induced Zener Tunneling effect, recombine with electrons in the emitter region. Analysis of temperature dependent measurements, thermal resistance, and the measured EL spectra revealed the presence of severe self-heating effects.

Huili Grace Xing - One of the best experts on this subject based on the ideXlab platform.

  • molecular beam epitaxy of polar iii nitride Resonant Tunneling Diodes
    2021
    Co-Authors: Jimy Encomendero, Debdeep Jena, S M Islam, Huili Grace Xing
    Abstract:

    Advances in molecular beam epitaxy (MBE) have been crucial for the engineering of heterostructures in which the wave nature of electrons dictates carrier transport dynamics. These advances led to the first demonstration of negative differential conductance (NDC) in arsenide-based Resonant Tunneling Diodes (RTDs) in 1974. In contrast to the 17 years elapsed between the initial MBE growth of arsenide semiconductors and the first demonstration of room-temperature GaAs/AlAs RTDs, the development of polar III-nitride RTDs has been remarkably different. After pioneering growths of nitride materials by MBE in 1973, it would take 43 years—until 2016—to demonstrate the first GaN/AlN RTD that exhibits repeatable NDC at room temperature. Here, we discuss, from the crystal growth point of view, the key developments in the epitaxy of III-nitride heterostructures that have led us to the demonstration of robust Resonant Tunneling transport and reliable NDC in III-nitride semiconductors. We show that in situ tracking of the crystal electron diffraction allows us to deterministically control the number of monolayers incorporated into the Tunneling barriers of the active region. Employing this technique, we fabricate various GaN/AlN RTD designs showing the exponential enhancement of the Resonant Tunneling current as a function of barrier thickness. In addition, we experimentally demonstrate that Tunneling transport in nitride RTDs is sensitive to epitaxial parameters such as the substrate growth temperature and threading dislocation density. This new insight into the MBE growth of nitride Resonant Tunneling devices represents a significant step forward in the engineering of new functionalities within the family of III-nitride semiconductors, allowing to harness quantum interference effects for the new generation of electronic and photonic devices.

  • n polar gan aln Resonant Tunneling Diodes
    2020
    Co-Authors: Yongjin Cho, Jimy Encomendero, Huili Grace Xing, Debdeep Jena
    Abstract:

    N-polar GaN/AlN Resonant Tunneling Diodes are realized on single-crystal N-polar GaN bulk substrate by plasma-assisted molecular beam epitaxy growth. The room-temperature current-voltage characteristics reveal a negative differential conductance (NDC) region with a peak Tunneling current of 6.8$\pm$ 0.8 kA/cm$^2$ at a forward bias of ~8 V. Under reverse bias, the polarization-induced threshold voltage is measured at ~$-$4 V. These Resonant and threshold voltages are well explained with the polarization field which is opposite to that of the metal-polar counterpart, confirming the N-polarity of the RTDs. When the device is biased in the NDC-region, electronic oscillations are generated in the external circuit, attesting to the robustness of the Resonant Tunneling phenomenon. In contrast to metal-polar RTDs, N-polar structures have the emitter on the top of the Resonant Tunneling cavity. As a consequence, this device architecture opens up the possibility of seamlessly interfacing$-$via Resonant Tunneling injection$-$a wide range of exotic materials with III-nitride semiconductors, providing a route to explore new device physics.

  • n polar gan aln Resonant Tunneling Diodes
    2020
    Co-Authors: Yongjin Cho, Jimy Encomendero, Huili Grace Xing, Debdeep Jena
    Abstract:

    N-polar GaN/AlN Resonant Tunneling Diodes are realized on a single-crystal N-polar GaN bulk substrate by plasma-assisted molecular beam epitaxy growth. The room-temperature current–voltage characteristics reveal a negative differential conductance (NDC) region with a peak Tunneling current of 6.8 ± 0.8 kA/cm2 at a forward bias of ∼8 V. Under reverse bias, the polarization-induced threshold voltage is measured at ∼ − 4 V. These Resonant and threshold voltages are well explained with the polarization field, which is opposite to that of the metal-polar counterpart, confirming the N-polarity of the Resonant Tunneling Diodes (RTDs). When the device is biased in the NDC-region, electronic oscillations are generated in the external circuit, attesting to the robustness of the Resonant Tunneling phenomenon. In contrast to metal-polar RTDs, N-polar structures have the emitter on the top of the Resonant Tunneling cavity. As a consequence, this device architecture opens up the possibility of seamlessly interfacing—via Resonant Tunneling injection—a wide range of exotic materials with III-nitride semiconductors, providing a route towards unexplored device physics.

  • fighting broken symmetry with doping toward polar Resonant Tunneling Diodes with symmetric characteristics
    2020
    Co-Authors: Jimy Encomendero, Debdeep Jena, Vladimir Protasenko, Farhan Rana, Huili Grace Xing
    Abstract:

    The recent demonstration of Resonant Tunneling transport in nitride semiconductors has led to an invigorated effort to harness this quantum transport regime for practical applications. In polar semiconductors, however, the interplay between fixed polarization charges and mobile free carriers leads to asymmetric transport characteristics. Here, we investigate the possibility of using degenerately doped contact layers to screen the built-in polarization fields and recover symmetric Resonant injection. Thanks to a high doping density, negative differential conductance is observed under both bias polarities of $\mathrm{Ga}\mathrm{N}$/$\mathrm{Al}\mathrm{N}$ Resonant Tunneling Diodes (RTDs). Moreover, our analytical model reveals a lower bound for the minimum Resonant-Tunneling voltage achieved via uniform doping, owing to the dopant solubility limit. Charge storage dynamics is also studied by impedance measurements, showing that at close-to-equilibrium conditions, polar RTDs behave effectively as parallel-plate capacitors. These mechanisms are completely reproduced by our analytical model, providing a theoretical framework useful in the design and analysis of polar Resonant-Tunneling devices.

  • room temperature microwave oscillations in gan aln Resonant Tunneling Diodes with peak current densities up to 220 ka cm2
    2018
    Co-Authors: Jimy Encomendero, Debdeep Jena, S M Islam, Vladimir Protasenko, Sergei Rouvimov, Patrick Fay, Rusen Yan, Amit Verma, Huili Grace Xing
    Abstract:

    We report the generation of room temperature microwave oscillations from GaN/AlN Resonant Tunneling Diodes, which exhibit record-high peak current densities. The Tunneling heterostructure grown by molecular beam epitaxy on freestanding GaN substrates comprises a thin GaN quantum well embedded between two AlN Tunneling barriers. The room temperature current-voltage characteristics exhibit a record-high maximum peak current density of ∼220 kA/cm2. When biased within the negative differential conductance region, microwave oscillations are measured with a fundamental frequency of ∼0.94 GHz, generating an output power of ∼3.0 μW. Both the fundamental frequency and the output power of the oscillator are limited by the external biasing circuit. Using a small-signal equivalent circuit model, the maximum intrinsic frequency of oscillation for these Diodes is predicted to be ∼200 GHz. This work represents a significant step towards microwave power generation enabled by Resonant Tunneling transport, an ultra-fast pr...