-
Berardi Sensale-Rodriguez,
Jia Guo,
Ronghua Wang,
Jai Verma, Guowang Li,
Tian Fang,
Edward Beam,
Andrew Ketterson,
Michael Schuette,
Paul Saunier,
Xiang Gao,
Shiping Guo,
Gregory Snider,
Patrick Fay,
Debdeep Jena,
Huili Grace Xing
Solid-State Electronics 01/2013; 80:67 - 71. · 1.40 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Monolayer of hexagonal boron nitride (h-BN), commonly known as "white
graphene" is a promising wide bandgap semiconducting material for
deep-ultaviolet optoelectronic devices. In this report, the light absorption of
a single layer hexagonal boron nitride is calculated using a tight-binding
Hamiltonian. The absorption is found to be monotonically decreasing function of
photon energy compared to graphene where absorption coefficient is independent
of photon energy and characterized by the effective fine-structure constant.
09/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: Lattice-matched depletion-mode InAlN/AlN/GaN high-electron mobility transistors (HEMTs) on a SiC substrate were fabricated, for the first time, with a dielectric-free passivation (DFP) process in which the device access region was treated by O<sub>2</sub>/Ar plasma. Similar to dielectric passivation using SiN and Al<sub>2</sub>O<sub>3</sub>, the plasma treatment can effectively shorten the gate-length extension. As a result, the current gain cutoff frequency fT of a 60-nm rectangular-gate HEMT increased from 125 to 210 GHz after the plasma DFP; this RF performance is among the highest reported fT for GaN-based HEMTs. The device showed a dc drain current density of 2.1 A/mm and a peak extrinsic transconductance of 487 mS/mm after DFP. The Lg-fTproduct of 12.6 GHz ·μm is among the highest reported for a gate-physical-length-to-barrier-thickness aspect ratio of 5.6. Small gate lag and drain lag are observed in pulsed I-V measurements with a 300-ns pulsewidth.
IEEE Electron Device Letters 08/2011; · 2.85 Impact Factor
-
Physica Status Solidi (A) Applications and Materials 06/2011; 208(7):1620 - 1622. · 1.46 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report high-electron mobility nitride heterostructures with >70% Al composition AlGaN alloy barriers grown by molecular beam epitaxy. Direct growth of such AlGaN layers on GaN resulted in hexagonal trenches and a low mobility polarization-induced charge. By applying growth interruption at the heterojunction, the surface morphology improved dramatically and the room temperature two-dimensional electron gas (2DEG) mobility increased by an order of magnitude, exceeding 1300 cm2/V s. The 2DEG density was tunable at 0.4–3.7×1013/cm2 by varying the total barrier thickness (t). Surface barrier heights of the heterostructures were extracted and exhibited dependence on t.
Applied Physics Letters 11/2010; 97(22):222110-222110-3. · 3.84 Impact Factor
-
Debdeep Jena,
John Simon,
Albert,
Wang,
Yu Cao,
Kevin Goodman,
Jai Verma,
Satyaki Ganguly, Guowang Li,
Kamal Karda,
Vladimir Protasenko,
Chuanxin Lian,
Thomas Kosel,
Patrick Fay,
Huili Xing
[show abstract]
[hide abstract]
ABSTRACT: The role of spontaneous and piezoelectric polarization in III-V nitride heterostructure devices is discussed. Problems as well as opportunities in incorporating polarization in abrupt and graded heterojunctions composed of binary, ternary, and quaternary nitrides are outlined. Comment: 7 pages, 5 figures
10/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: The first demonstration of high-Al-composition (> 70%) AlGaN high electron mobility transistors (HEMTs) is reported. High electron mobility (~1300 cm<sup>2</sup>/Vs at room temperature) was achieved in novel high-Al-composition AlGaN 2-D electron gas structures. The threshold voltages (V<sub>th</sub>) of Al<sub>0.72</sub>Ga<sub>0.28</sub>N/AlN/GaN HEMTs were shifted from -1.0 to -0.13 V by employing different gate metal stacks, Al/Au and Ni/Au, respectively. With a 4-nm Al<sub>2</sub>O<sub>3</sub> gate dielectric on top of the nitride heterostructures, the ~0.9-eV work-function difference between Al and Ni induced ~0.9-V V<sub>th</sub> shift in the pairs of the Al/Au and Ni/Au gate HEMTs, which indicates that the Fermi level is unpinned at the ALD Al<sub>2</sub>O<sub>3</sub>/AlGaN interface. The results were reproducible for HEMTs of various gate lengths. The results suggest that it is possible to obtain enhancement- and depletion-mode AlGaN HEMTs using work-function engineering which can enable integrated monolithic digital circuits without postgrowth recess etching or ion implantation.
IEEE Electron Device Letters 10/2010; · 2.85 Impact Factor
-
Ronghua Wang,
Xiu Xing,
Tian Fang,
T. Zimmermann,
Chuanxin Lian, Guowang Li,
P. Saunier,
Xiang Gao,
Shiping Guo,
G. Snider,
P. Fay,
D. Jena,
Huili Xing
[show abstract]
[hide abstract]
ABSTRACT: Due to the high two-dimensional electron gas (2DEG) concentration and high temperature stability, lattice matched InAlN/AlN/GaN high electron mobility transistors (HEMTs) have attracted tremendous amount of interest for high-power and high-frequency electronics. Employing the gate recess technology, a popular way to develop enhancement-mode (E-mode) devices for digital and mixed signal applications, record high performance (output current density of 2 A/mm, extrinsic transconductance of 890 mS/mm, and f<sub>t</sub>/f<sub>max</sub> of 95/135 GHz for 150-nm gate length) have been very recently reported on E-mode InAIN HEMTs. Temperature dependent characterization of the subthreshold slope (SS) can provide valuable information on the interface states and their distribution near the band edges. In this paper, we have performed the field-effect measurements on these gate-recessed E-mod InAIN HEMTs, and extracted the interface states from the temperature dependent SS from 80 to 300 K.
Device Research Conference (DRC), 2010; 07/2010
-
[show abstract]
[hide abstract]
ABSTRACT: Graphene nanoribbons (GNRs) were fabricated by metal mask lithography and plasma etching. GNRs with width ∼ 20 nm show field-effect conductance modulation of ∼ 12 at room temperature and >106 at 4.2 K. Conductance quantization due to quantum confinement in low field transport was observed. Landauer formula was utilized to fit the experimental data and excellent agreement was obtained. The extracted subband energy separation was found to deviate from the predicted values of perfect armchair GNRs. Transmission probability is much smaller than unity due to scattering by GNR edge/bulk disorder and impurities, indicating a mean free path ∼ 40 nm. High field family I-Vs exhibited current saturation tendency and current density as high as 2 A/mm has been measured at low temperature.
Applied Physics Letters 03/2010; 96(10):103109-103109-3. · 3.84 Impact Factor
