The Experts below are selected from a list of 6345 Experts worldwide ranked by ideXlab platform
U. K. Mishra - One of the best experts on this subject based on the ideXlab platform.
-
investigation of nitrogen polar p type doped gan alxga 1 x n superlattices for applications in wide bandgap p type field effect transistors
Applied Physics Letters, 2019Co-Authors: Athith Krishna, Aditya Raj, Nirupam Hatui, Stacia Keller, U. K. MishraAbstract:In this study, the metal-organic chemical vapor deposition growth and electrical properties of N-polar Modulation doped p-AlGaN/GaN superlattices (SLs) were investigated. Hole sheet charge density and mobility were studied as a function of the concentration of the p-type dopant Mg in the SL and the number of SL periods. Room temperature Hall measurements were carried out to determine the hole mobility and the sheet charge density. While the hole density increased with the increasing number of SL periods, the hole mobility was largely unaffected. Hole mobilities as high as 18 cm2/V s at a simultaneously high hole density of 6.5 × 1013 cm−2 were observed for N-polar SLs with a Mg Modulation Doping of 7.5 × 1018 cm−3. For comparable uniformly doped Ga-polar SL samples, a mobility of 11 cm2/V s was measured. These results confirm the presence of abrupt Mg Doping profiles in N-polar p-type GaN/AlxGa(1−x)N SL, allowing the demonstration of SLs with properties comparable to those of state-of-the-art Ga-polar Modulation doped AlGaN/GaN SLs grown using molecular beam epitaxy. The lowest sheet resistance in the GaN/AlGaN material system of 5 kΩ/◻ is also reported. Test-structure transistors were also fabricated to investigate the applicability of these SL structures, with the planar device resulting in a current of 5 mA/mm and a FinFET structure resulting in a current of over 100 mA/mm.In this study, the metal-organic chemical vapor deposition growth and electrical properties of N-polar Modulation doped p-AlGaN/GaN superlattices (SLs) were investigated. Hole sheet charge density and mobility were studied as a function of the concentration of the p-type dopant Mg in the SL and the number of SL periods. Room temperature Hall measurements were carried out to determine the hole mobility and the sheet charge density. While the hole density increased with the increasing number of SL periods, the hole mobility was largely unaffected. Hole mobilities as high as 18 cm2/V s at a simultaneously high hole density of 6.5 × 1013 cm−2 were observed for N-polar SLs with a Mg Modulation Doping of 7.5 × 1018 cm−3. For comparable uniformly doped Ga-polar SL samples, a mobility of 11 cm2/V s was measured. These results confirm the presence of abrupt Mg Doping profiles in N-polar p-type GaN/AlxGa(1−x)N SL, allowing the demonstration of SLs with properties comparable to those of state-of-the-art Ga-polar mod...
-
investigation of nitrogen polar p type doped gan alxga 1 x n superlattices for applications in wide bandgap p type field effect transistors
arXiv: Applied Physics, 2019Co-Authors: Athith Krishna, Aditya Raj, Nirupam Hatui, Stacia Keller, U. K. MishraAbstract:In this study the MOCVD growth and electrical properties of N-polar Modulation doped p-AlGaN/GaN superlattices (SLs) were investigated. Hole sheet charge density and mobility were studied as a function of the concentration of the p-type dopant Mg in the SL and the number of SL periods. Room temperature Hall measurements were carried out to determine the hole mobility and the sheet charge density. While the hole density increased with increasing number of SL periods, the hole mobility was largely unaffected.Hole mobilities as high as 18cm2/Vs at a simultaneous high hole density of 6.5e13 cm-2 were observed for N-polar SLs with a Mg Modulation Doping of 7.5e18 cm-3. For comparable uniformly doped Ga-polar SL samples, a mobility of 11cm2/Vs was measured. Lowest sheet resistance in the GaN/AlGaN materials system of 5kOhm/sq is also reported. Test-structure transistors were also fabricated to investigate the applicability of these SL structures, with planar device resulting in a current of 5mA/mm, and a FinFET structure resulting in a current of over 100mA/mm.
-
high performance n face gan microwave mis hemts with 70 power added efficiency
IEEE Electron Device Letters, 2009Co-Authors: Man Hoi Wong, Yi Pei, David F. Brown, James S. Speck, S Keller, U. K. MishraAbstract:A high-performance N-face GaN metal-insulator-semiconductor high-electron-mobility transistor was fabricated. A dual-AlN back-barrier scheme was developed using polarization engineering to provide a large total dipole moment, which allowed enhanced Modulation Doping for a higher 2-D electron gas density without parallel conduction. Devices with 0.6-mum gate length showed an fT and f max of 17 and 58 GHz, respectively. A highest power-added efficiency (PAE) of 71% at 4 GHz was measured in these devices with 20-V drain bias. At 28 V, an output power density of 6.4 W/mm with 67% PAE was achieved.
-
properties of n polar algan gan heterostructures and field effect transistors grown by metalorganic chemical vapor deposition
Journal of Applied Physics, 2008Co-Authors: S Keller, James S. Speck, Siddharth Rajan, C S Suh, Z Chen, Rongming Chu, N A Fichtenbaum, Motoko Furukawa, Steven P Denbaars, U. K. MishraAbstract:Smooth N-polar GaN/AlxGa1−xN/GaN heterostructures with a different Al mole fraction were grown by metalorganic chemical vapor deposition on (0001) sapphire substrates with a misorientation angle of 4° toward the a-sapphire plane. The sheet electron density of the two-dimensional electron gas (2DEG), which formed at the upper GaN/AlxGa1−xN interface increased with an increasing Al-mole fraction in the AlxGa1−xN layer and increasing silicon Modulation Doping, similar to the observations for Ga-polar heterostructures. The transport properties of the 2DEG, however, were anisotropic. The growth on vicinal substrates led to the formation of well ordered multiatomic steps during AlxGa1−xN growth and the sheet resistance of the 2DEG parallel to the steps was about 25% lower than the resistance measured in the perpendicular direction. The fabricated devices exhibited a drain-source current, IDS, of 0.9 A/mm at a gate-source voltage +1 V. At a drain-source voltage of 10 V and IDS=300 mA/mm, current-gain and maximum...
John E Bowers - One of the best experts on this subject based on the ideXlab platform.
-
on quantum dot lasing at gain peak with linewidth enhancement factor α h 0
APL Photonics (Web), 2020Co-Authors: Weng W Chow, Zeyu Zhang, Justin Norman, Songtao Liu, John E BowersAbstract:This paper describes an investigation of the linewidth enhancement factor αH in a semiconductor quantum-dot laser. Results are presented for active region parameters and laser configurations important for minimizing αH. In particular, the feasibility of lasing at the gain peak with αH = 0 is explored. The study uses a many-body theory with dephasing effects from carrier scattering treated at the level of quantum-kinetic equations. InAs quantum-dot lasers with different p-Modulation Doping densities are fabricated and measured to verify the calculated criteria on laser cavity design and epitaxial growth conditions.This paper describes an investigation of the linewidth enhancement factor αH in a semiconductor quantum-dot laser. Results are presented for active region parameters and laser configurations important for minimizing αH. In particular, the feasibility of lasing at the gain peak with αH = 0 is explored. The study uses a many-body theory with dephasing effects from carrier scattering treated at the level of quantum-kinetic equations. InAs quantum-dot lasers with different p-Modulation Doping densities are fabricated and measured to verify the calculated criteria on laser cavity design and epitaxial growth conditions.
-
high performance continuous wave 1 3 μm quantum dot lasers on silicon
Applied Physics Letters, 2014Co-Authors: Chong Zhang, Justin Norman, Andrew Snyder, D Lubyshev, J M Fastenau, Arthur C Gossard, John E BowersAbstract:We demonstrate record performance 1.3 μm InAs quantum dot lasers grown on silicon by molecular beam epitaxy. Ridge waveguide lasers fabricated from the as-grown material achieve room temperature continuous wave thresholds as low as 16 mA, output powers exceeding 176 mW, and lasing up to 119 °C. P-Modulation Doping of the active region improves T0 to the range of 100–200 K while maintaining low thresholds and high output powers. Device yield is presented showing repeatable performance across different dies and wafers.
T J Badcock - One of the best experts on this subject based on the ideXlab platform.
-
low threshold current density and negative characteristic temperature 1 3 μm inas self assembled quantum dot lasers
Applied Physics Letters, 2007Co-Authors: T J Badcock, K M Groom, M Hopkinson, D J Mowbray, M S Skolnick, Huiyun Liu, R J Royce, Q JiangAbstract:By combining optimized growth of the GaAs spacer layers and p-type Modulation Doping of the quantum dots, a 1.3μm emitting self-assembled quantum dot laser exhibiting both a low threshold current density and negative-T0 temperature behavior at room temperature is achieved. Spontaneous emission measurements provide no evidence for enhanced Auger recombination in doped devices. The negative T0 exhibited by the doped device is consistent with a delayed thermalization of carriers within the quantum dot ensemble.
-
observation and modeling of a room temperature negative characteristic temperature 1 3 mu m p type Modulation doped quantum dot laser
IEEE Journal of Quantum Electronics, 2006Co-Authors: Chaoyuan Jin, T J Badcock, K M Groom, D J Mowbray, Huiyun Liu, R J Royce, M HopkinsonAbstract:A room-temperature negative characteristic temperature (T0 ) and ultralow threshold current density (Jth) of 48 Amiddotcm-2 are demonstrated for a 1.3-mum InAs quantum dot laser. These characteristics are obtained by combining a high-growth-temperature GaAs spacer layer with p-type Modulation Doping of the quantum dots in multiple layer dot-in-a-well structures. Through a comparison of p-doped and undoped devices, a photon coupling mechanism is proposed to account for the different temperature dependences of Jth for the two devices. Numerical simulations based on a rate equation model, which includes photon coupling between ground and excited quantum dot states, are performed. The simulations are able to account for the very different temperature-dependent Jth behavior of the doped and undoped device
-
1 3 micro sign m inas gaas quantum dot laser with low threshold current density and negative characteristic temperature above room temperature
Electronics Letters, 2006Co-Authors: T J Badcock, H Y Liu, K M Groom, Chaoyuan Jin, M Gutierrez, M Hopkinson, D J Mowbray, M S SkolnickAbstract:The combination of a high-growth-temperature GaAs spacer layer and p-type Modulation Doping has been utilised to obtain a low-threshold-current-density, high-temperature-stability 1.3 µm InAs/GaAs quantum-dot laser. A room-temperature threshold current density of 48 A/cm2 and a negative characteristic temperature over the temperature range from −50 to 40°C is achieved for a five-layer device with as-cleaved facets.
M Hopkinson - One of the best experts on this subject based on the ideXlab platform.
-
low threshold current density and negative characteristic temperature 1 3 μm inas self assembled quantum dot lasers
Applied Physics Letters, 2007Co-Authors: T J Badcock, K M Groom, M Hopkinson, D J Mowbray, M S Skolnick, Huiyun Liu, R J Royce, Q JiangAbstract:By combining optimized growth of the GaAs spacer layers and p-type Modulation Doping of the quantum dots, a 1.3μm emitting self-assembled quantum dot laser exhibiting both a low threshold current density and negative-T0 temperature behavior at room temperature is achieved. Spontaneous emission measurements provide no evidence for enhanced Auger recombination in doped devices. The negative T0 exhibited by the doped device is consistent with a delayed thermalization of carriers within the quantum dot ensemble.
-
observation and modeling of a room temperature negative characteristic temperature 1 3 mu m p type Modulation doped quantum dot laser
IEEE Journal of Quantum Electronics, 2006Co-Authors: Chaoyuan Jin, T J Badcock, K M Groom, D J Mowbray, Huiyun Liu, R J Royce, M HopkinsonAbstract:A room-temperature negative characteristic temperature (T0 ) and ultralow threshold current density (Jth) of 48 Amiddotcm-2 are demonstrated for a 1.3-mum InAs quantum dot laser. These characteristics are obtained by combining a high-growth-temperature GaAs spacer layer with p-type Modulation Doping of the quantum dots in multiple layer dot-in-a-well structures. Through a comparison of p-doped and undoped devices, a photon coupling mechanism is proposed to account for the different temperature dependences of Jth for the two devices. Numerical simulations based on a rate equation model, which includes photon coupling between ground and excited quantum dot states, are performed. The simulations are able to account for the very different temperature-dependent Jth behavior of the doped and undoped device
-
1 3 micro sign m inas gaas quantum dot laser with low threshold current density and negative characteristic temperature above room temperature
Electronics Letters, 2006Co-Authors: T J Badcock, H Y Liu, K M Groom, Chaoyuan Jin, M Gutierrez, M Hopkinson, D J Mowbray, M S SkolnickAbstract:The combination of a high-growth-temperature GaAs spacer layer and p-type Modulation Doping has been utilised to obtain a low-threshold-current-density, high-temperature-stability 1.3 µm InAs/GaAs quantum-dot laser. A room-temperature threshold current density of 48 A/cm2 and a negative characteristic temperature over the temperature range from −50 to 40°C is achieved for a five-layer device with as-cleaved facets.
Zhifeng Ren - One of the best experts on this subject based on the ideXlab platform.
-
fabrication of low cost thermoelectric materials with improved properties using Modulation Doping strategy
ASME 2012 Heat Transfer Summer Conference collocated with the ASME 2012 Fluids Engineering Division Summer Meeting and the ASME 2012 10th Internationa, 2012Co-Authors: Mona Zebarjadi, Mildred S Dresselhaus, Gang Chen, Zhifeng RenAbstract:We introduce the Modulation-Doping strategy in bulk SiGe nanostructures to improve the thermoelectric power factor. By separating charge carriers from their parent atoms via embedding heavily doped nanoparticles inside an intrinsic host matrix, the ionized impurity scattering rate could be largely reduced, resulting in enhanced mobility. By band engineering, the carriers can spill over from nanoparticles into the host matrix, resulting in similar carrier concentrations, Fermi levels and consequently Seebeck coefficients as those of the uniform nanocomposites. In addition, nanoparticles with low thermal conductivities can further reduce the overall thermal conductivity of the sample. Combining the enhanced electrical conductivity, the reduced thermal conductivity and the unaffected Seebeck coefficient, we were able to enhance the thermoelectric properties of Si-rich Si95Ge5. And therefore were able to fabricate a low-cost sample with a competitive performance as those of the state of the art Si80Ge20.Copyright © 2012 by ASME
-
fabrication of low cost thermoelectric materials with improved properties using Modulation Doping strategy
ASME, 2012Co-Authors: Mona Zebarjadi, Mildred S Dresselhaus, Gang Chen, Zhifeng RenAbstract:Solid-State Solar-Thermal Energy Conversion Center (United States. Department of Energy. Office of Basic Energy Sciences award number DESC0001299/DE-FG02-09ER46577)
-
enhancement of thermoelectric properties by Modulation Doping in silicon germanium alloy nanocomposites
Nano Letters, 2012Co-Authors: Mona Zebarjadi, Mildred S Dresselhaus, Gang Chen, Hui Wang, Kevin Lukas, Hengzhi Wang, Dezhi Wang, Cyril Opeil, Zhifeng RenAbstract:Modulation-Doping was theoretically proposed and experimentally proved to be effective in increasing the power factor of nanocomposites (Si80Ge20)70(Si100B5)30 by increasing the carrier mobility but not the figure-of-merit (ZT) due to the increased thermal conductivity. Here we report an alternative materials design, using alloy Si70Ge30 instead of Si as the nanoparticles and Si95Ge5 as the matrix, to increase the power factor but not the thermal conductivity, leading to a ZT of 1.3 ± 0.1 at 900 °C.
-
power factor enhancement by Modulation Doping in bulk nanocomposites
Nano Letters, 2011Co-Authors: Mona Zebarjadi, Giri Joshi, Gaohua Zhu, Austin J Minnich, Yucheng Lan, Xiaowei Wang, Mildred S Dresselhaus, Zhifeng Ren, Gang ChenAbstract:We introduce the concept of Modulation Doping in three-dimensional nanostructured bulk materials to increase the thermoelectric figure of merit. Modulation-doped samples are made of two types of nanograins (a two-phase composite), where dopants are incorporated only into one type. By band engineering, charge carriers could be separated from their parent grains and moved into undoped grains, which would result in enhanced mobility of the carriers in comparison to uniform Doping due to a reduction of ionized impurity scattering. The electrical conductivity of the two-phase composite can exceed that of the individual components, leading to a higher power factor. We here demonstrate the concept via experiment using composites made of doped silicon nanograins and intrinsic silicon germanium grains.