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5 Mar 2012

Volume 100, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 100, 101903 (2012); http://dx.doi.org/10.1063/1.3673327 (3 pages)

Michael Ian Lapsley, Anaram Shahravan, Qingzhen Hao, Bala Krishna Juluri, Stephen Giardinelli, Mengqian Lu, Yanhui Zhao, I-Kao Chiang, Themis Matsoukas, and Tony Jun Huang
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Contact length scaling in graphene field-effect transistors

Haitao Xu, Sheng Wang, Zhiyong Zhang, Zhenxing Wang, Huilong Xu, and Lian-Mao Peng

Appl. Phys. Lett. 100, 103501 (2012); http://dx.doi.org/10.1063/1.3691629 (4 pages) | Cited 4 times

Online Publication Date: 5 March 2012

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A study is performed on the contact length scaling in graphene field effect transistors. When the contact length (LC) is below the transfer length (LT), both transconductance and on-current increase rapidly with LC due to the strengthened carrier injection. Over the transfer length, the transconductance keeps increasing prominently before coming to a saturation. A possible explanation is that larger contact length would induce deeper doping in graphene, and the nonlinear screening of metal-induced charge could modify the potential barrier, which subsequently adjusts the contact resistance and transconductance. In principle, the electron-hole asymmetry can be tuned via altering the contact lengths.
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85.30.Tv Field effect devices

Effects of interface disorder on valley splitting in SiGe/Si/SiGe quantum wells

Zhengping Jiang, Neerav Kharche, Timothy Boykin, and Gerhard Klimeck

Appl. Phys. Lett. 100, 103502 (2012); http://dx.doi.org/10.1063/1.3692174 (4 pages)

Online Publication Date: 6 March 2012

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A sharp potential barrier at the Si/SiGe interface introduces valley splitting (VS), which lifts the 2-fold valley degeneracy in strained SiGe/Si/SiGe quantum wells (QWs). This work examines in detail the effects of Si/SiGe interface disorder on the VS in an atomistic tight binding approach based on statistical sampling. VS is analyzed as a function of electric field, QW thickness, and simulation domain size. Strong electric fields push the electron wavefunctions into the SiGe buffer and introduce significant VS variations from device to device. A Gedankenexperiment with ordered alloys sheds light on the importance of different bonding configurations on VS. We conclude that a single SiGe band offset and effective mass cannot comprehend the complex Si/SiGe interface interactions that dominate VS.
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73.21.Fg Quantum wells
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.20.Nr Semiconductor compounds

Carrier dynamics and design optimization of electrolyte-induced inversion layer carbon nanotube-silicon Schottky junction solar cell

Wenchao Chen, Gyungseon Seol, Andrew G. Rinzler, and Jing Guo

Appl. Phys. Lett. 100, 103503 (2012); http://dx.doi.org/10.1063/1.3693377 (4 pages) | Cited 3 times

Online Publication Date: 6 March 2012

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Carrier dynamics of the electrolyte-induced inversion layer carbon nanotube-silicon Schottky junction solar cells is explored by numerical simulations. Operation mechanisms of the solar cells with and without the electrolyte-induced inversion layer are presented and compared, which clarifies the current flow mechanisms in a solar cell with an induced inversion layer. A heavily doped back contact layer can behave as a hole block layer. In addition to lowering contact resistance and surface recombination, it is particularly useful for improving carrier separation in an electrolyte-induced inversion layer solar cell or a metal-insulator-semiconductor grating solar cell.
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88.40.jp Multijunction solar cells

Near infrared electroluminescence from n-InN/p-GaN light-emitting diodes

Guo-Guang Wu, Wan-Cheng Li, Chun-Sheng Shen, Fu-Bin Gao, Hong-Wei Liang, Hui Wang, Li-Jun Song, and Guo-Tong Du

Appl. Phys. Lett. 100, 103504 (2012); http://dx.doi.org/10.1063/1.3693150 (3 pages) | Cited 2 times

Online Publication Date: 7 March 2012

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Undoped InN thin film was grown on p-GaN/Al2O3 (0001) template by molecular beam epitaxy. Near-infrared (NIR) electroluminescence (EL) that overlapped the optical communication wavelength range was realized using the n-InN/p-GaN heterojunction structure. The light emitting diode showed typical rectification characteristics with a turn-on voltage of around 0.8 V. A dominant narrow NIR emission peak was achieved from the InN side under applied forward bias. By comparing with the photoluminescence spectrum, the EL emission peak at 1573 nm was attributed to the band-edge emission of the InN film.
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85.60.Jb Light-emitting devices

Plasmonic quantum dot solar cells for enhanced infrared response

Hao Feng Lu, Sudha Mokkapati, Lan Fu, Greg Jolley, Hark Hoe Tan, and Chennupati Jagadish

Appl. Phys. Lett. 100, 103505 (2012); http://dx.doi.org/10.1063/1.3691917 (4 pages) | Cited 2 times

Online Publication Date: 7 March 2012

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Enhanced near infrared photoresponse in plasmonic InGaAs/GaAs quantum dot solar cells (QDSC) is demonstrated. Long wavelength light absorption in the wetting-layer and quantum-dot region of the quantum dot solar cell is enhanced through scattering of light by silver nanoparticles deposited on the solar cell surface. Plasmonic light trapping results in simultaneous increase in short-circuit current density by 5.3% and open circuit voltage by 0.9% in the QDSC, leading to an overall efficiency enhancement of 7.6%.
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88.40.hj Efficiency and performance of solar cells
73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Bz Metals and metallic alloys
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors

Ultra-broadband microwave metamaterial absorber

Fei Ding, Yanxia Cui, Xiaochen Ge, Yi Jin, and Sailing He

Appl. Phys. Lett. 100, 103506 (2012); http://dx.doi.org/10.1063/1.3692178 (4 pages) | Cited 11 times

Online Publication Date: 9 March 2012

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A microwave ultra-broadband polarization-independent metamaterial absorber is demonstrated. It is composed of a periodic array of metal-dielectric multilayered quadrangular frustum pyramids. These pyramids possess resonant absorption modes at multi-frequencies, of which the overlapping leads to the total absorption of the incident wave over an ultra-wide spectral band. The experimental absorption at normal incidence is above 90% in the frequency range of 7.8–14.7 GHz, and the absorption is kept large when the incident angle is smaller than 60°. The experimental results agree well with the numerical simulation.
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42.70.-a Optical materials

A tunable acoustic diode made by a metal plate with periodical structure

Hong-xiang Sun, Shu-yi Zhang, and Xiu-ji Shui

Appl. Phys. Lett. 100, 103507 (2012); http://dx.doi.org/10.1063/1.3693374 (4 pages) | Cited 5 times

Online Publication Date: 9 March 2012

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A model of acoustic diodes is realized by a thin brass plate with single-sided periodical grating structure immersed in water and studied both numerically and experimentally. The unidirectional transmission of acoustic waves is identified in two different frequency ranges, which can be systematically controlled by adjusting the sizes of the structural units. The results indicate that the acoustic diodes have the advantages of tunable frequency range, broader bandwidth, and simple structure as well as being easy to be achieved. The remarkable unidirectional transmission effect has great potential applications in ultrasonic devices, such as acoustic rectifiers, acoustic diodes, and related fields.
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43.38.-p Transduction; acoustical devices for the generation and reproduction of sound
43.30.-k Underwater sound
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