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19 Apr 2010

Volume 96, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 96, 163101 (2010); http://dx.doi.org/10.1063/1.3327831 (3 pages)

Ramesh Nath, Seungbum Hong, Jeffrey A. Klug, Alexandra Imre, Michael J. Bedzyk, Ram S. Katiyar, and Orlando Auciello
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The transport and quantum capacitance properties of epitaxial graphene

J. L. Xia, Fang Chen, J. L. Tedesco, D. K. Gaskill, R. L. Myers-Ward, C. R. Eddy, D. K. Ferry, and N. J. Tao

Appl. Phys. Lett. 96, 162101 (2010); http://dx.doi.org/10.1063/1.3396982 (3 pages) | Cited 7 times

Online Publication Date: 19 April 2010

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Epitaxial graphene field effect transistors were fabricated, characterized, and studied. Both the capacitance and transport measurements were performed on the same devices using an electrochemical gate. The quantum capacitance of the epitaxial graphene was extracted, which was similar to that of exfoliated graphene near the Dirac point, but it exhibits a large sublinear behavior at high carrier densities. The recently developed self-consistent theory for charged impurities in graphene is found to provide a reasonable description of the transport data, but a more complete theory is needed to explain both the transport and quantum capacitance data for the epitaxial graphene devices.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Geminate electron-hole recombination in organic solids in the presence of a donor-acceptor heterojunction

Mariusz Wojcik, Przemyslaw Michalak, and M. Tachiya

Appl. Phys. Lett. 96, 162102 (2010); http://dx.doi.org/10.1063/1.3397992 (3 pages) | Cited 6 times

Online Publication Date: 19 April 2010

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Geminate electron-hole recombination is one of the main factors limiting the efficiency of organic solar cells. We present a systematic study of this process based on both analytical and simulation models. We determine how the charge-pair separation probability is affected by the hopping length of charge carriers, the presence of a donor-acceptor heterojunction, electron and hole mobilities, and other factors. We show that the charge-pair separation probability of an electron and a hole which are initially at the contact distance is maximized when the electron and hole mobilities are equal to each other.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.Ee Mobility edges; hopping transport
72.20.Fr Low-field transport and mobility; piezoresistance

Long range resonant tunneling in quantum cascade structures

A. Buffaz, M. Carras, L. Doyennette, V. Trinité, X. Marcadet, and V. Berger

Appl. Phys. Lett. 96, 162103 (2010); http://dx.doi.org/10.1063/1.3399768 (3 pages) | Cited 5 times

Online Publication Date: 19 April 2010

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Tunneling transport in a quantum cascade detector is investigated. With regard to coherent transport in quantum cascade lasers, a Kazarinov–Suris approach R. F. Kazarinov and R. A. Suris, [Sov. Phys. Semicond. 6, 120 (1972)] needs to be modified through the introduction of an additional Fermi–Dirac factor in order to properly model the experimental data at low temperature. Electronic current is completely dominated by tunneling transport; the model here presented should help to suppress it in the future design of efficient quantum cascade detectors.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Effect of atomically controlled interfaces on Fermi-level pinning at metal/Ge interfaces

K. Yamane, K. Hamaya, Y. Ando, Y. Enomoto, K. Yamamoto, T. Sadoh, and M. Miyao

Appl. Phys. Lett. 96, 162104 (2010); http://dx.doi.org/10.1063/1.3368701 (3 pages) | Cited 14 times

Online Publication Date: 19 April 2010

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We study electrical properties of metal/Ge contacts with an atomically controlled interface, and compare them with those with a disordered one, where atomically controlled interfaces can be demonstrated by using Fe3Si/Ge(111) contacts. We find that the Schottky barrier height of Fe3Si/n-Ge(111) contacts is unexpectedly lower than those induced by the strong Fermi-level pinning at other metal/n-Ge contacts. For Fe3Si/p-Ge(111) contacts, we identify clear rectifying behavior in I-V characteristics at low temperatures, which is also different from I-V features due to the strong Fermi-level pinning at other metal/p-Ge contacts. These results indicate that there is an extrinsic contribution such as dangling bonds to the Fermi-level pinning effect at the directly connected metal/Ge contacts.
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73.40.Ns Metal-nonmetal contacts
73.20.At Surface states, band structure, electron density of states
71.55.-i Impurity and defect levels
73.30.+y Surface double layers, Schottky barriers, and work functions

Modeling of porous silicon junction field effect transistor gas sensors: Insight into NO2 interaction

G. Barillaro, G. M. Lazzerini, and L. M. Strambini

Appl. Phys. Lett. 96, 162105 (2010); http://dx.doi.org/10.1063/1.3391620 (3 pages) | Cited 2 times

Online Publication Date: 20 April 2010

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In this paper a lumped parameter electrical model for porous silicon junction field effect transistor (PSJFET) gas sensors is presented and experimentally validated. The PSJFET is an integrated p-channel JFET device modified with a porous silicon layer, the latter acting as sensing element. The model is described by using an analytical closed-form expression, which quantitatively links the sensor current to the analyte concentration in the environment, and validated by using experimental data of PSJFETs exposed to both synthetic air and NO2 with concentration of 300 ppb. Best fitting of experimental data with the proposed model allows one to get quantitative information on the effect of NO2 adsorption/desorption at the PS surface on electrical PS parameters, such as its conductance and surface charge density.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Electronic channels for acoustic transport in semiconductor heterostructures

K. Biermann, O. D. D. Couto, W. Seidel, R. Hey, and P. V. Santos

Appl. Phys. Lett. 96, 162106 (2010); http://dx.doi.org/10.1063/1.3407672 (3 pages) | Cited 3 times

Online Publication Date: 21 April 2010

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We demonstrate electronic waveguides for the ambipolar transport of electrons and holes by surface acoustic waves (SAWs) in buried (Al,Ga)As quantum well (QW) structures, which do not require deep-etching for their fabrication. They are defined by tailoring the SAW-induced piezoelectric potential in the QW plane using thin metal stripes deposited onto the piezoelectric cap layer of the QW sample. Acoustic transport experiments show the enhanced capture and acoustic transport of photoexcited carriers underneath the metallic surface stripes.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
43.20.Mv Waveguides, wave propagation in tubes and ducts
85.35.Ds Quantum interference devices
73.23.-b Electronic transport in mesoscopic systems
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Gate-defined double quantum dot with integrated charge sensors realized in InGaAs/InP by incorporating a high-κ dielectric

Jie Sun, Marcus Larsson, Ivan Maximov, and H. Q. Xu

Appl. Phys. Lett. 96, 162107 (2010); http://dx.doi.org/10.1063/1.3409223 (3 pages) | Cited 3 times

Online Publication Date: 21 April 2010

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A gate-defined double quantum dot with two integrated quantum point contact charge sensors is realized in an InGaAs/InP heterostructure by employing a high-κ HfO2 thin film as gate dielectric and a polymer bridge technique. Clear honeycomb patterns are observed in the measured charge stability diagram of the double quantum dot and charge sensing signals of the quantum point contacts. It is also found that the quantum point contact charge sensors can detect the charge states in the double quantum dot even in the condition that the direct transport signal is not visible.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Thermoelectric properties of polycrystalline In4Se3 and In4Te3

Xun Shi, Jung Y. Cho, James R. Salvador, Jihui Yang, and Hsin Wang

Appl. Phys. Lett. 96, 162108 (2010); http://dx.doi.org/10.1063/1.3389494 (3 pages) | Cited 16 times

Online Publication Date: 21 April 2010

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High thermoelectric performance of a single crystal layered compound In4Se3 was reported recently. We present here an electrical and thermal transport property study over a wide temperature range for polycrystalline samples of In4Se3 and In4Te3. Our data demonstrate that these materials are lightly doped semiconductors, leading to large thermopower and resistivity. Very low thermal conductivity, below 1 W/m K, is observed. The power factors for In4Se3 and In4Te3 are much smaller when compared with state-of-the-art thermoelectric materials. This combined with the very low thermal conductivity results in the maximum ZT value of less than 0.6 at 700 K for In4Se3.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
66.70.Df Metals, alloys, and semiconductors

Effect of surface passivation on generation and recombination lifetimes in silicon wafer studied by impedance spectroscopy

Sanjai Kumar, P. K. Singh, and S. R. Dhariwal

Appl. Phys. Lett. 96, 162109 (2010); http://dx.doi.org/10.1063/1.3385779 (3 pages) | Cited 2 times

Online Publication Date: 22 April 2010

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Impedance spectroscopy is used to study the effect of surface passivation on minority carrier lifetimes. The technique allows measurement of generation and recombination lifetimes separately. Induced p+-p-n structures are prepared by depositing semitransparent layers of high and low work function metals (Pd and Al, respectively) on the two sides of silicon wafers. Hydrogen adsorption property of Pd surface has been utilized for passivation. The generation lifetimes remain almost unaffected but recombination lifetimes enhance many folds after passivations which are in agreement with values obtained by microwave photoconductive decay technique after chemical passivation. Variations are analyzed for estimation of bulk recombination lifetime.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Cg Contact resistance, contact potential
68.43.Mn Adsorption kinetics

Band alignment at the BaCuSeF/ZnTe interface

Andriy Zakutayev, Janet Tate, Heather A. S. Platt, Douglas A. Keszler, Alireza Barati, Andreas Klein, and Wolfram Jaegermann

Appl. Phys. Lett. 96, 162110 (2010); http://dx.doi.org/10.1063/1.3405757 (3 pages) | Cited 2 times

Online Publication Date: 22 April 2010

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In situ photoemission spectroscopy experiments are used to characterize the interface between ZnTe and the wide band gap p-type semiconductor BaCuSeF. The contact is characterized by a null valence-band offset, a large conduction-band offset, and a chemically graded interface. By applying the transitivity rule for band offset and on the basis of similarities in chemical composition, BaCuSeF contact to chalcogenide photovoltaic absorber materials would be expected to have similar properties. By extension, BaCuChF (Ch = S,Se,Te) materials are suitable as p-layers in p-i-n double-heterojunction solar cells fabricated with CdTe, Cu(InGa)Se2, and Cu2ZnSnS4 absorbers.
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73.20.At Surface states, band structure, electron density of states
71.20.Nr Semiconductor compounds
79.60.Jv Interfaces; heterostructures; nanostructures
88.40.J- Types of solar cells

Depth-dependence of electrical conductivity of diamondlike carbon films

A. Sikora, P. Paolino, H. Ftouni, C. Guerret-Piécourt, J.-L. Garden, A.-S. Loir, F. Garrelie, C. Donnet, and O. Bourgeois

Appl. Phys. Lett. 96, 162111 (2010); http://dx.doi.org/10.1063/1.3407671 (3 pages) | Cited 1 time

Online Publication Date: 23 April 2010

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The electrical behavior of diamondlike carbon (DLC) has been measured as a function of depth. The amorphous carbon (a-C) films are deposited by pulsed laser deposition using two complementary setups: a femtosecond (fs) and a nanosecond (ns) pulse lasers. It is demonstrated through four probe resistance measurements and contact resistance mapping that the fs DLC are electrically heterogeneous in thickness. The presence of a thick sp2 rich layer on top is evidenced for fs a-C and is apparently away in the sp3 rich ns a-C. It is attributed to different subplantation processes between ns and fs a-C films.
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73.61.Wp Fullerenes and related materials
81.15.Fg Pulsed laser ablation deposition
73.40.Cg Contact resistance, contact potential

Scattering mechanism in modulation-doped shallow two-dimensional electron gases

D. Laroche, S. Das Sarma, G. Gervais, M. P. Lilly, and J. L. Reno

Appl. Phys. Lett. 96, 162112 (2010); http://dx.doi.org/10.1063/1.3402765 (3 pages) | Cited 4 times

Online Publication Date: 23 April 2010

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We report on a systematic investigation of the dominant scattering mechanism in shallow two-dimensional electron gases (2DEGs) formed in modulation-doped GaAs/AlxGa1−xAs heterostructures. The power-law exponent of the electron mobility versus density, μ∝nα, is extracted as a function of the 2DEG’s depth. When shallower than 130 nm from the surface, the power-law exponent of the 2DEG, as well as the mobility, drops from α ≃ 1.65 (130 nm deep) to α ≃ 1.3 (60 nm deep). Our results for shallow 2DEGs are consistent with theoretical expectations for scattering by remote dopants, in contrast to the mobility-limiting background charged impurities of deeper heterostructures.
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73.20.At Surface states, band structure, electron density of states
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