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21 May 2001

Volume 78, Issue 21, pp. 3163-3363

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Measurement of ballistic phonon conduction near hotspots in silicon

P. G. Sverdrup, S. Sinha, M. Asheghi, S. Uma, and K. E. Goodson

Appl. Phys. Lett. 78, 3331 (2001); http://dx.doi.org/10.1063/1.1371536 (3 pages) | Cited 20 times

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The Fourier law for lattice heat conduction fails when the source of heat is small compared to the phonon mean free path. We provide experimental evidence for this effect using heating and electrical-resistance thermometry along a doped region in a suspended silicon membrane. The data are consistent with a closed-form two-fluid phonon conduction model, which accounts for the severe departure from equilibrium at the hotspot. The temperature rise exceeds predictions based on the Fourier law by 60% when the phonon mean free path is a factor of 30 larger than the resistor thickness. This work is improving the constitutive modeling of heat flow in deep-submicron transistors. © 2001 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.20.-e Phonons in crystal lattices

Vertical p-type high-mobility heterojunction metal–oxide–semiconductor field-effect transistors

Xiangdong Chen, Qiqing Ouyang, Sankaran Kartik Jayanarayanan, Freek E. Prins, and Sanjay Banerjee

Appl. Phys. Lett. 78, 3334 (2001); http://dx.doi.org/10.1063/1.1375004 (3 pages) | Cited 1 time

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We have fabricated a vertical p-channel metal–oxide–semiconductor field-effect transistor called high-mobility heterojunction transistor (HMHJT). Compared with a Si control device, reduced short channel effects, reduced floating body effect, and high drive current have been achieved with this device structure. A SiGe/Si heterojunction barrier at the source/bulk junction suppresses drain induced barrier lowering and bulk punchthrough, which are significant problems for sub-100 nm devices. A SiGe source also helps to reduce the charge built-up in the floating body. The higher mobility in a strained SiGe channel and the absence of a hetero-barrier between the source and channel result in higher drive current. The fabricated HMHJT has a 60% higher drive current at VDS = VGS−VT = −1.6 V, and a 70× lower off-state leakage current at VDS = −1.6 V and VGS = 0.0 V, compared with the Si control device. © 2001 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Current crowding and optical saturation effects in GaInN/GaN light-emitting diodes grown on insulating substrates

X. Guo and E. F. Schubert

Appl. Phys. Lett. 78, 3337 (2001); http://dx.doi.org/10.1063/1.1372359 (3 pages) | Cited 65 times

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Current crowding in mesa-structure GaInN/GaN light emitting diodes (LEDs) grown on insulating substrates is analyzed. A model developed reveals an exponential decrease of the current density with distance from the mesa edge. Devices with stripe-shaped mesa geometry display current crowding and a saturation of the optical output power at high injection currents. It is shown that the optical power saturation depends on the device geometry. It is also shown that saturation is less pronounced in LEDs employing a ring-shaped mesa geometry, which reduces current crowding, as compared to the conventional square-shaped mesa geometry. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.60.Bt Optoelectronic device characterization, design, and modeling

Low-noise photodetectors based on heterojunctions of AlGaN–GaN

V. V. Kuryatkov, H. Temkin, J. C. Campbell, and R. D. Dupuis

Appl. Phys. Lett. 78, 3340 (2001); http://dx.doi.org/10.1063/1.1351852 (3 pages) | Cited 20 times

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We describe detailed current–voltage and noise measurements carried out on AlGaN–GaN heterojunction photodetectors. Dark current densities below 1×10−10 A/cm2 are measured at a bias level of −5 V, at room temperature. In diodes with a diameter of 50 μm, low leakage currents result in the zero-bias noise spectral density as low as 3.6×10−32 A2/Hz. Based on the combined electrical and noise measurements, we calculate room-temperature thermally limited specific detectivity greater than 2.4×1014 cm Hz1/2 W−1. Background-limited specific detectivity exceeds 3.5×1013 cm Hz1/2 W−1. © 2001 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
72.80.Ey III-V and II-VI semiconductors
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.40.+w Photoconduction and photovoltaic effects

Transparent organic light-emitting diodes using metal acethylacetonate complexes as an electron injective buffer layer

Asuka Yamamori, Sachiko Hayashi, Toshiki Koyama, and Yoshio Taniguchi

Appl. Phys. Lett. 78, 3343 (2001); http://dx.doi.org/10.1063/1.1359485 (3 pages) | Cited 37 times

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We studied transparent organic light-emitting diodes, which had a transparent top electrode deposited by sputtering, for possible application to a transparent light-emitting display. In the fabrication of a transparent electrode on an organic layer, steps must be taken to reduce the damage incurred by the organic layer during the sputter deposition process. We report the results of our study where we found that we could reduce the damage to the organic layer by suppressing the temperature rise of substrate resulting from the intermittent plasma irradiation. We also found that a thin film of metal acethylacetonate complexes [Mt(acac)2] is useful as a buffer layer to prevent an underlying emission layer from incurring damage in the sputter process. In previous reports, a thin film of copper phthalocyanine (CuPc) was used as an electron injective buffer layer. However, the absorption of the CuPc Q bands at λ = 620 and 665 nm decreased the total optical transmission of the device. Transmittance in the visible region of our device reached ∼ 90%, because Mt(acac)2 has no absorption properties that reduce the transmittance of visible light. The device using Ni(acac)2 as a buffer layer showed better electron injection properties and luminance of 1500 cd/m2 than the one using CuPc. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
81.15.Cd Deposition by sputtering
78.40.Me Organic compounds and polymers

Negative differential photoconductivity in quantum-dot infrared photodetectors

V. Ryzhii

Appl. Phys. Lett. 78, 3346 (2001); http://dx.doi.org/10.1063/1.1373414 (3 pages) | Cited 13 times

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We present a simple model for quantum-dot infrared photodetectors (QDIPs) describing nontrivial (decreasing) dependences of the photocurrent on the QD density and the applied voltage. It is shown that recent experiments demonstrating a negative differential photoconductivity in QDIPs can be interpreted in terms of this model. The effects under consideration can be attributed to the repulsive potential of charged quantum dots and heating of mobile electrons influencing the rate of the electron capture. Qualitative distinctions between the QDIP photocurrent–voltage and dark current–voltage characteristics are explained as well. © 2001 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.63.Kv Quantum dots
73.50.Pz Photoconduction and photovoltaic effects
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.La Quantum dots

Band alignment at a ZnO/GaN (0001) heterointerface

Soon-Ku Hong, Takashi Hanada, Hisao Makino, Yefan Chen, Hang-Ju Ko, Takafumi Yao, Akinori Tanaka, Hiroyuki Sasaki, and Shigeru Sato

Appl. Phys. Lett. 78, 3349 (2001); http://dx.doi.org/10.1063/1.1372339 (3 pages) | Cited 55 times

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We report the experimental results of the valence band offset at a ZnO/GaN (0001) heterointerface. The ZnO/GaN (0001) heterointerface is prepared by growing a ZnO layer on (0001) GaN/Al2O3, in which the ZnO layer is epitaxially deposited by plasma-assisted molecular-beam epitaxy, while the GaN template is prepared by metalorganic chemical-vapor deposition. Ex situ ultraviolet and x-ray photoelectron spectroscopy have been used to measure the valence band offset ΔEV. The photoelectron spectroscopy measurements are done before and after Ar+ ion cleaning of the surfaces. Type-II band alignments with band offsets of ΔEV = 1.0 eV (before cleaning) and 0.8 eV (after cleaning) with the valence band maximum of GaN being placed above that of ZnO are obtained. © 2001 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
79.60.Jv Interfaces; heterostructures; nanostructures
81.65.Cf Surface cleaning, etching, patterning
81.05.Dz II-VI semiconductors
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