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4 Oct 2004

Volume 85, Issue 14, pp. 2679-2983

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 2860 (2004); http://dx.doi.org/10.1063/1.1799245 (3 pages)

Priya Mahadevan and Alex Zunger
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Control of flatband voltage of Si-based metal–oxide–semiconductor diodes by inclusion of cesium ions in silicon dioxide

Takuya Kobayashi, Kazuki Tanaka, Osamu Maida, and Hikaru Kobayashi

Appl. Phys. Lett. 85, 2806 (2004); http://dx.doi.org/10.1063/1.1799232 (3 pages) | Cited 1 time

Online Publication Date: 14 October 2004

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The flatband voltage of Si-based metal–oxide–semiconductor diodes can be controlled by the inclusion of cesium (Cs) in SiO2 layers. The inclusion of Cs can be achieved by two methods: (1) spin-on of cesium chloride aqueous solutions, and (2) evaporation of Cs. The maximum flatband voltage shift of ∼0.8 V is achieved by the Cs evaporation method and, in this case, the Cs concentration is estimated to be ∼1013 atoms∕cm2 from total reflection x-ray fluorospectroscopy measurements. Even when the Cs concentration is as low as ∼1010 atoms∕cm2, ∼0.1 V flatband voltage shift can be achieved. The net positive charge of Cs decreases with the Cs concentration.
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85.30.Kk Junction diodes
61.72.S- Impurities in crystals
78.70.En X-ray emission spectra and fluorescence

Enhanced current densities in Au∕molecule∕GaAs devices

Saurabh Lodha and David B. Janes

Appl. Phys. Lett. 85, 2809 (2004); http://dx.doi.org/10.1063/1.1799235 (3 pages) | Cited 14 times

Online Publication Date: 14 October 2004

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Metal–molecule–semiconductor heterostructures have been studied in a Au∕molecule∕p-type GaAs configuration. Stable monolayers of alkane and aromatic thiols were self-assembled from solution on heavily doped p-type (p+) GaAs surfaces. A low-energy, indirect path technique was used to evaporate Au on the molecular layer to minimize damage or penetration of the layer. Electrical characteristics of the devices were evaluated by current–voltage (I–V) measurements. In comparison to Au∕p+-GaAs control samples, which show rectifying behavior expected for Schottky barriers, the Au∕molecule∕p+-GaAs structures exhibit higher conductances and less rectification. The results indicate strong molecular coupling to the contacts with a significant density of molecular states near the Fermi level. A simple electrostatic model, which considers the dielectric constant and dipole charge of the molecular layer as well as the GaAs depletion region, has been developed to explain the observed characteristics. Variable temperature I–V measurements exhibit very little temperature dependence, consistent with tunneling-based transport through the molecular layer.
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85.30.De Semiconductor-device characterization, design, and modeling
73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
77.22.Ch Permittivity (dielectric function)

Evaluation of the gauge factor for membranes assembled by single-walled carbon nanotubes

A. Reale, P. Regoliosi, L. Tocca, P. Lugli, S. Orlanducci, M. L. Terranova, and G. Bruni

Appl. Phys. Lett. 85, 2812 (2004); http://dx.doi.org/10.1063/1.1783018 (3 pages) | Cited 2 times

Online Publication Date: 14 October 2004

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Samples of single-walled carbon nanotubes (SWCNTs) organized in the form of thin membranes have been investigated in order to correlate the mechanical deformation and conductivity behavior of such nanosized material. The nanotubes gauge factor of piezoresistivity has been evaluated by comparing the electrical responses induced by the deformation in SWCNT membranes and in Si substrates with the same electrical characteristics. The gauge factor of the SWCNT–Si systems was found to be a factor 2.3–2.5 larger than that of the Si substrates. We have also observed that temperature slightly enhances the piezoresistive response of the SWCNT.
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72.20.Fr Low-field transport and mobility; piezoresistance
61.46.-w Structure of nanoscale materials
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep

Effects of hydrogen annealing on heteroepitaxial-Ge layers on Si: Surface roughness and electrical quality

Ammar Nayfeh, Chi On Chui, Krishna C. Saraswat, and Takao Yonehara

Appl. Phys. Lett. 85, 2815 (2004); http://dx.doi.org/10.1063/1.1802381 (3 pages) | Cited 37 times

Online Publication Date: 14 October 2004

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We have studied the effect of hydrogen annealing on the surface roughness of germanium (Ge) layers grown by chemical vapor deposition on silicon using atomic force microscopy and cross-sectional high resolution scanning electron microscopy (HR-SEM). Our results indicate a strong reduction of roughness that approaches 90% at 825 °C. The smoother Ge surface allowed for the fabrication of metal-oxide-semiconductor capacitors using germanium oxynitride (GeOxNy) as the gate dielectric. Electrical quality was studied using high frequency capacitance–voltage characteristic of epi-Ge showing negligible hysteresis. We discuss the results in terms of Ge–H cluster formation, which lowers the diffusion barrier, allowing for higher diffusivity and surface mobility. The temperature dependence shows tapering off for temperatures exceeding 800 °C, indicating a barrier reduction of ∼92 meV.
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81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
68.37.Ps Atomic force microscopy (AFM)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
68.35.Fx Diffusion; interface formation
73.61.Cw Elemental semiconductors

Near-field optical microscopy and scanning Kelvin microscopy studies of V-defects on AlGaN∕GaN films

C. S. Ku, J. M. Peng, W. C. Ke, H. Y. Huang, N. E. Tang, W. K. Chen, W. H. Chen, and M. C. Lee

Appl. Phys. Lett. 85, 2818 (2004); http://dx.doi.org/10.1063/1.1799248 (3 pages) | Cited 2 times

Online Publication Date: 14 October 2004

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AlxGa1−xN thin film was grown on undoped GaN∕sapphire (0001) substrate by metalorganic chemical vapor deposition. V-defects were directly observed by atomic force microscopy (AFM) with various size of 0.5–2 μm in diameter. In a previous study, the microphotoluminescence spectra showed an extra peak (Iv=350 nm) inside the V-defect besides the near-band-edge emission (Inbe=335 nm). To achieve better spatial resolution, we used near-field scanning optical microscopy (NSOM) and scanning Kelvin-force microscopy (SKM) to probe the V-defect in detail. The NSOM spectra showed that the intensity of the Iv band increased gradually from V-defect edges to its center, while Inbe remained unchanged. Besides, the SKM measurements revealed that the Fermi level decreased from the flat region to V-defect center by about 0.2 eV. These results suggest that the Iv band could be related to shallow acceptor levels, likely resulting from VGa defects.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
71.20.Nr Semiconductor compounds
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.37.Ps Atomic force microscopy (AFM)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Rashba effect on the plasma oscillations in a coupled bilayer of electrons and holes

Godfrey Gumbs

Appl. Phys. Lett. 85, 2821 (2004); http://dx.doi.org/10.1063/1.1800276 (3 pages) | Cited 3 times

Online Publication Date: 14 October 2004

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We consider the effect of spin-orbit (SO) coupling on the plasma oscillations for a coupled system of two-dimensional electron or heavy hole (HH) gases. The Rashba effect lifts the degeneracy of the energy spectrum and produces a linear term for electrons but a cubic term for HH states in wave vector space. The SO coupling gives rise to two plasmon branches for a single layer due to transitions within a subband and between subbands. The interlayer coupling splits each of these branches. We present numerical results for the frequency of the collective excitations as a function of wave vector and the Rashba parameter. The application to optical characterization studies is discussed.
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.21.Fg Quantum wells

Quantum cascade photodetector

L. Gendron, M. Carras, A. Huynh, V. Ortiz, C. Koeniguer, and V. Berger

Appl. Phys. Lett. 85, 2824 (2004); http://dx.doi.org/10.1063/1.1781731 (3 pages) | Cited 50 times

Online Publication Date: 14 October 2004

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A photovoltaic intersubband detector based on electron transfer on a cascade of quantum levels is presented: A quantum cascade detector (QCD). The highest photoresponse of intersubband transition-based photovoltaic detectors is demonstrated: 35 mA∕W at null bias. The deduced absorption is of the same order of magnitude as that of a classical quantum-well infrared photodetector, i.e., 20%. Because they work with no dark current, QCDs are very promising for small-pixel large focal plane array applications.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
78.67.De Quantum wells
78.30.Fs III-V and II-VI semiconductors
73.21.Fg Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.66.Fd III-V semiconductors
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Formation of Ga interstitials in (Al,In)yGa1−yNxP1−x alloys and their role in carrier recombination

N. Q. Thinh, I. P. Vorona, M. Izadifard, I. A. Buyanova, W. M. Chen, Y. G. Hong, H. P. Xin, and C. W. Tu

Appl. Phys. Lett. 85, 2827 (2004); http://dx.doi.org/10.1063/1.1803918 (3 pages) | Cited 9 times

Online Publication Date: 14 October 2004

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Formation of complex defects involving a Ga interstitial (Gai) in (Al,In)yGa1−yNxP1−x alloys and their effects on optical quality are studied by photoluminescence (PL) and optically detected magnetic resonance spectroscopies. Introduction of these defects is shown to be largely promoted by incorporation of N. In quaternary alloys, concentrations of the defects are found to critically depend on the group III atoms that replace Ga, i.e., it is largely enhanced by the presence of Al in alloys, but is only marginally affected by In incorporation. The effect is attributed to differences in surface adatom mobilities of the group III atoms involved and their bonding strength with N. The revealed Gai complexes are shown to act as efficient nonradiative recombination centers degrading the PL efficiency. The defects exhibit high thermal stability and can only be partially removed by postgrowth rapid thermal annealing.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
78.55.Cr III-V semiconductors
61.72.J- Point defects and defect clusters
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.66.Fd III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Near-band edge light emission from silicon semiconductor on insulator diodes

J. Zhao, G. Zhang, T. Trupke, A. Wang, F. Hudert, and M. A. Green

Appl. Phys. Lett. 85, 2830 (2004); http://dx.doi.org/10.1063/1.1800286 (3 pages) | Cited 8 times

Online Publication Date: 14 October 2004

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Light-emitting diodes have been designed and fabricated on commercial crystalline silicon semiconductor on insulator wafers. Strong infrared light emission has been observed from these diodes under forward bias conditions with an external quantum efficiency of 2×10−6. The band edge phonon-assisted photoluminescence from the top single-crystalline silicon layer is responsible for such emission with a spectrum peaked at 1.135 μm wavelength. Due to negligible reabsorption of spontaneously emitted photons within the extremely thin silicon layer, the short wavelength emission is significantly stronger in relative terms compared to emission from bulk-silicon light-emitting devices.
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85.60.Jb Light-emitting devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
78.60.Fi Electroluminescence
78.55.-m Photoluminescence, properties and materials

Tailored conductivity behavior in nanocrystalline nickel ferrite

Babita Baruwati, K. Madhusudan Reddy, Sunkara V. Manorama, Rajnish K. Singh, and Om Parkash

Appl. Phys. Lett. 85, 2833 (2004); http://dx.doi.org/10.1063/1.1801685 (3 pages) | Cited 19 times

Online Publication Date: 14 October 2004

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In this letter, we report an important issue in nanoparticle synthesis by the “bottom up” approach. By controlling the pH of the starting mixture of the salts we have been successful in obtaining the desired conductivity of nanosized nickel ferrite. X-ray diffraction and transmission electron microscopy confirmed the size, structure, and morphology of the nanoferrites. All the materials are typical semiconducting oxides whose conductivity depends on the pH of the starting salt solution. Direct current and alternating current conductivity studies coupled with thermoelectric measurements and the resultant activation energies help us to propose the mechanism of conductivity in these ferrites. X-ray photoelectron spectroscopy studies are indicative of Ni3+ presence in p-type ferrite. The n- and p-type conductivity in these materials is attributed to the hopping due to the presence of Fe3+ and Ni3+ ions, respectively.
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75.50.Gg Ferrimagnetics
75.50.Pp Magnetic semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.-w Structure of nanoscale materials
72.20.Ee Mobility edges; hopping transport
72.20.Pa Thermoelectric and thermomagnetic effects
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Lp Transmission electron microscopy (TEM)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Positional control of self-assembled quantum dots by patterning nanoscale SiN islands

H. Gotoh, H. Kamada, T. Saitoh, S. Shigemori, and J. Temmyo

Appl. Phys. Lett. 85, 2836 (2004); http://dx.doi.org/10.1063/1.1804251 (3 pages) | Cited 1 time

Online Publication Date: 14 October 2004

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We propose a method for obtaining position-controlled self-assembled quantum dots. The self-assembled InGaAs quantum dots are grown on a GaAs (311) B substrate on which SiN islands have been patterned using a nanolithographic technique. The SiN pattern determines the position of the quantum dots as well as their optical properties. The positional uniformity and photoluminescence spectrum strongly depend on the pitch of the SiN pattern. At an optimum pitch, uniformly arranged quantum dots and intense photoluminescence spectra with sharp peaks are obtained.
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81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials
81.07.Ta Quantum dots
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
78.55.Cr III-V semiconductors
81.16.Dn Self-assembly
78.67.Hc Quantum dots
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Structure adjustment during high-deposition-rate growth of microcrystalline silicon solar cells

Y. Mai, S. Klein, X. Geng, and F. Finger

Appl. Phys. Lett. 85, 2839 (2004); http://dx.doi.org/10.1063/1.1801676 (3 pages) | Cited 18 times

Online Publication Date: 14 October 2004

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Preparation of microcrystalline silicon for solar cell applications is investigated under high-pressure, high-power conditions with plasma-enhanced chemical vapor deposition at 95 MHz. It is found that the deposition rate depends mainly on the amount of silane in the reaction zone. Changes in the discharge power affect the deposition rate very little. This points to silane depletion under these process conditions. The amount of H radicals, on the other hand, increases with increasing discharge power and leads to structure changes of the material. Making use of this effect, optimum phase mixture material at the transition from highly crystalline to amorphous growth can be deposited at considerably higher deposition rates without loss in solar cell performance.
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84.60.Jt Photoelectric conversion
81.05.Cy Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
62.50.-p High-pressure effects in solids and liquids
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