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24 Jul 2006

Volume 89, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 041105 (2006); http://dx.doi.org/10.1063/1.2234591 (3 pages)

Alireza Khalili, Hopil Bae, and James S. Harris
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Low-resistance Ohmic contacts for high-power GaN field-effect transistors obtained by selective area growth using plasma-assisted molecular beam epitaxy

Seung Jae Hong and Kyekyoon (Kevin) Kim

Appl. Phys. Lett. 89, 042101 (2006); http://dx.doi.org/10.1063/1.2234566 (3 pages) | Cited 10 times

Online Publication Date: 24 July 2006

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Selective area growth (SAG) has been demonstrated using plasma-assisted molecular beam epitaxy (PAMBE) resulting in vastly improved Ohmic contacts for GaN-based high-power field-effect transistors (FETs). A heavily doped n-GaN layer was grown only in the Ohmic contact region and the resulting nonalloyed Ti/Al/Ti/Au metal contacts exhibited linear Ohmic behavior. Through rapid thermal annealing, very low specific contact resistivity (1.8×10−8 Ω cm2) was obtained at 850 °C. Furthermore, contact resistances below 0.8 Ω mm were obtained by annealing at a wide range of temperatures (750–950 °C). GaN metal-semiconductor FETs were fabricated to investigate the effect of the PAMBE-SAG on device performance, producing great improvement in the dc characteristics.
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85.30.Tv Field effect devices

Metal precipitation at grain boundaries in silicon: Dependence on grain boundary character and dislocation decoration

T. Buonassisi, A. A. Istratov, M. D. Pickett, M. A. Marcus, T. F. Ciszek, and E. R. Weber

Appl. Phys. Lett. 89, 042102 (2006); http://dx.doi.org/10.1063/1.2234570 (3 pages) | Cited 30 times

Online Publication Date: 24 July 2006

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Synchrotron-based analytical microprobe techniques, electron backscatter diffraction, and defect etching are combined to determine the dependence of metal silicide precipitate formation on grain boundary character and microstructure in multicrystalline silicon (mc-Si). Metal silicide precipitate decoration is observed to increase with decreasing atomic coincidence within the grain boundary plane (increasing Σ values). A few low-Σ boundaries contain anomalously high metal precipitate concentrations, concomitant with heavy dislocation decoration. These results provide direct experimental evidence that the degree of interaction between metals and structural defects in mc-Si can vary as a function of microstructure, with implications for mc-Si device performance and processing.
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81.05.Bx Metals, semimetals, and alloys
81.05.Cy Elemental semiconductors
81.30.Mh Solid-phase precipitation
61.72.Mm Grain and twin boundaries
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.65.Cf Surface cleaning, etching, patterning

Valence band structure and band offset of 3C- and 4H-SiC studied by ballistic hole emission microscopy

K.-B. Park, Y. Ding, J. P. Pelz, P. G. Neudeck, and A. J. Trunek

Appl. Phys. Lett. 89, 042103 (2006); http://dx.doi.org/10.1063/1.2218302 (3 pages) | Cited 3 times

Online Publication Date: 24 July 2006

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p-type Schottky barriers in Pt/3C-SiC contacts have been measured using ballistic hole emission microscopy (BHEM) and estimated to be ∼ 0.06 eV higher than identically prepared Pt/p-type 4H-SiC contacts. This indicates the 3C-SiC valence band maximum (VBM) is ∼ 0.06 eV below the 4H-SiC VBM, consistent with the calculated ∼ 0.05 eV type-II valence band offset between these polytypes. We also observe no evidence of an additional VBM in 3C-SiC, which supports the proposal that the second VBM observed in BHEM spectra on 4H-SiC is a crystal-field split VBM located ∼ 110 meV below the highest VBM.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
71.20.Nr Semiconductor compounds

Evidence of electron and hole inversion in GaAs metal-oxide-semiconductor capacitors with HfO2 gate dielectrics and α-Si/SiO2 interlayers

S. J. Koester, E. W. Kiewra, Yanning Sun, D. A. Neumayer, J. A. Ott, M. Copel, D. K. Sadana, D. J. Webb, J. Fompeyrine, J.-P. Locquet, C. Marchiori, M. Sousa, and R. Germann

Appl. Phys. Lett. 89, 042104 (2006); http://dx.doi.org/10.1063/1.2235862 (3 pages) | Cited 25 times

Online Publication Date: 25 July 2006

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Evidence of inversion in GaAs metal-oxide-semiconductor capacitors with HfO2 gate dielectrics and α-Si/SiO2 interlayers is reported. Capacitors formed on n-GaAs with atomic layer-deposited HfO2 displayed C-V characteristics with minimum Dit of 7×1011 cm−2/eV, while capacitors with molecular beam epitaxy-deposited HfO2 on p-GaAs had Dit = 3×1012 cm−2/eV. Lateral charge transport was confirmed using illuminated C-V measurements on capacitors fabricated with thick Al electrodes. Under these conditions, capacitors on n-GaAs (p-GaAs) showed “low-frequency” C-V behavior, indicated by a sharp capacitance increase and saturation at negative (positive) gate bias, confirming the presence of mobile charge at the semiconductor/dielectric interface.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors

Electric readout of magnetization dynamics in a ferromagnet-semiconductor system

Ł. Cywiński, H. Dery, and L. J. Sham

Appl. Phys. Lett. 89, 042105 (2006); http://dx.doi.org/10.1063/1.2235881 (3 pages) | Cited 5 times

Online Publication Date: 25 July 2006

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We apply an analysis of time-dependent spin-polarized current in a semiconductor channel at room temperature to establish how the magnetization configuration and dynamics of three ferromagnetic terminals, two of them biased and third connected to a capacitor, affect the currents and voltages. In a steady state, the voltage on the capacitor is related to spin accumulation in the channel. When the magnetization of one of the terminals is rotated, a transient current is triggered. This effect can be used for electrical detection of magnetization reversal dynamics of an electrode or for dynamical readout of the alignment of two magnetic contacts.
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73.40.Ns Metal-nonmetal contacts
75.60.Jk Magnetization reversal mechanisms
72.25.-b Spin polarized transport
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Identification of acceptor states in Li-doped p-type ZnO thin films

Y. J. Zeng, Z. Z. Ye, J. G. Lu, W. Z. Xu, L. P. Zhu, B. H. Zhao, and Sukit Limpijumnong

Appl. Phys. Lett. 89, 042106 (2006); http://dx.doi.org/10.1063/1.2236225 (3 pages) | Cited 47 times

Online Publication Date: 25 July 2006

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We investigate photoluminescence from reproducible Li-doped p-type ZnO thin films prepared by dc reactive magnetron sputtering. The LiZn acceptor state, with an energy level located at 150 meV above the valence band maximum, is identified from free-to-neutral-acceptor transitions. Another deeper acceptor state located at 250 meV emerges with the increased Li concentration. A broad emission centered at 2.96 eV is attributed to a donor-acceptor pair recombination involving zinc vacancy. In addition, two chemical bonding states of Li, evident in x-ray photoelectron spectroscopy, are probably associated with the two acceptor states observed.
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71.55.Gs II-VI semiconductors
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors

Low resistance nonalloyed Ni/Au Ohmic contacts to p-GaN irradiated by KrF excimer laser

Min-Suk Oh, Dae-Kue Hwang, Jae-Hong Lim, Chang-Goo Kang, and Seong-Ju Park

Appl. Phys. Lett. 89, 042107 (2006); http://dx.doi.org/10.1063/1.2236656 (3 pages) | Cited 3 times

Online Publication Date: 26 July 2006

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A specific contact resistance of 8.9×10−5 Ω cm2 was obtained for a Ni/Au Ohmic layer on the KrF laser-irradiated p-GaN. It was found that laser irradiation increases the hole concentration from 4.1×1017 to 9.7×1017 cm−3 by removing hydrogen atoms from p-GaN layer. The native oxide was also removed as evidenced by the Ga 2p peak shift and the decrease in the intensity of O 1s peak in the x-ray photoelectron spectra. The formation of a low resistance is attributed to the increase in the hole concentration and the removal of native oxide from p-GaN by laser irradiation.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.60.Jv Interfaces; heterostructures; nanostructures

Temperature effect on geminate recombination

J. Boch, F. Saigne, L. Dusseau, and R. D. Schrimpf

Appl. Phys. Lett. 89, 042108 (2006); http://dx.doi.org/10.1063/1.2236707 (3 pages) | Cited 2 times

Online Publication Date: 26 July 2006

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In this work, the Onsager equation has been numerically solved to investigate the temperature dependence of the initial recombination of electron-hole pairs in silicon dioxide at low electric field. In the 1980s, the temperature effect of the initial recombination was investigated on gate oxides in metal oxide semiconductor (MOS) devices at high electric field. The temperature dependence was shown to be negligible. In the investigation of total-dose effects on bipolar devices, the temperature dependence of the initial recombination has not been considered even though the electric field in the field oxide is much lower than for MOS gate oxides. The influence of the temperature on the initial separation distance between parent carriers in the geminate recombination case and its effect on the initial recombination have not been evaluated. Both last two points are studied in this work, showing a strong temperature dependence of the initial recombination at low electric field, representative of typical operating conditions in bipolar field oxides. This temperature dependence can have a significant effect on bipolar-device characterization.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Sk Insulators
77.22.Ch Permittivity (dielectric function)

Propagation of edge magnetoplasmons in semiconductor quantum-well structures

S. A. Mikhailov

Appl. Phys. Lett. 89, 042109 (2006); http://dx.doi.org/10.1063/1.2236866 (3 pages) | Cited 2 times

Online Publication Date: 26 July 2006

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The wavelength and the propagation length of the edge magnetoplasmons, running along the edge of a two-dimensional electron layer in a semiconductor quantum-well structure, are theoretically studied as a function of frequency, magnetic field, electron density, mobility, and geometry of the structure. The results are intended to be used for analysis and optimization of operation of recently invented quantum-well microwave spectrometers operating at liquid-nitrogen temperatures [ I. V. Kukushkin et al., Appl. Phys. Lett. 86, 044101 (2005) ].
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73.21.Fg Quantum wells
73.63.Hs Quantum wells
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Ee Mobility edges; hopping transport

Room temperature SiO2/SiO2 covalent bonding

Q.-Y. Tong, G. Fountain, and P. Enquist

Appl. Phys. Lett. 89, 042110 (2006); http://dx.doi.org/10.1063/1.2240232 (3 pages) | Cited 16 times

Online Publication Date: 26 July 2006

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Room temperature covalent bonds between bonded silicon oxide layers can be realized by forming surface and subsurface absorption layers followed by terminating outmost bonding surfaces with desired bonding groups prior to bonding. For example, by introducing fluorine into bonding oxide layers and NH2 groups onto surfaces of bonding oxide layers before bonding, bonding energy equivalent to silicon fracture energy (2500 mJ/m2) has been realized at room temperature after storage in air. Fluorine incorporation causes Si–O–Si ring breaking leading to fluorinated oxide formation with lower density, thus facilitating a higher diffusion rate of polymerization by-products and enhanced moisture absorptivity. Results indicate that by-products of the polymerization reaction between NH2 groups on mating surfaces appear to be more easily diffused and dispersed away from the bonding interface by the low density fluorinated oxide than are polymerization by-products of OH groups. This enhanced by-product removal results in covalent bonding at room temperature.
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82.35.-x Polymers: properties; reactions; polymerization
85.30.-z Semiconductor devices

Diffusion and activation of ultrashallow B implants in silicon on insulator: End-of-range defect dissolution and the buried Si/SiO2 interface

J. J. Hamilton, N. E. B. Cowern, J. A. Sharp, K. J. Kirkby, E. J. H. Collart, B. Colombeau, M. Bersani, D. Giubertoni, and A. Parisini

Appl. Phys. Lett. 89, 042111 (2006); http://dx.doi.org/10.1063/1.2240257 (3 pages) | Cited 10 times

Online Publication Date: 26 July 2006

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The fabrication of preamorphized p-type ultrashallow junctions in silicon-on-insulator (SOI) has been investigated. Electrical and structural measurements after annealing show that boron deactivation and transient enhanced diffusion are reduced in SOI compared to bulk wafers. The reduction is strongest when the end-of-range defects of the preamorphizing implant are located deep within the silicon overlayer of the SOI silicon substrate. Results reveal a very substantial increase in the dissolution rate of the end-of-range defect band. A key player in this effect is the buried Si/SiO2 interface, which acts as an efficient sink for interstitials competing with the silicon surface.
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66.30.J- Diffusion of impurities
71.55.-i Impurity and defect levels
61.72.up Other materials
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Ultralow surface recombination of c-Si substrates passivated by plasma-assisted atomic layer deposited Al2O3

B. Hoex, S. B. S. Heil, E. Langereis, M. C. M. van de Sanden, and W. M. M. Kessels

Appl. Phys. Lett. 89, 042112 (2006); http://dx.doi.org/10.1063/1.2240736 (3 pages) | Cited 79 times

Online Publication Date: 27 July 2006

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Excellent surface passivation of c-Si has been achieved by Al2O3 films prepared by plasma-assisted atomic layer deposition, yielding effective surface recombination velocities of 2 and 13 cm/s on low resistivity n- and p-type c-Si, respectively. These results obtained for ∼ 30 nm thick Al2O3 films are comparable to state-of-the-art results when employing thermal oxide as used in record-efficiency c-Si solar cells. A 7 nm thin Al2O3 film still yields an effective surface recombination velocity of 5 cm/s on n-type silicon.
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81.65.Rv Passivation
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.25.+i Surface conductivity and carrier phenomena
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Cw Elemental semiconductors

Measurement of the mean electron-hole pair ionization energy in 4H SiC

M. V. S. Chandrashekhar, Christopher I. Thomas, and Michael G. Spencer

Appl. Phys. Lett. 89, 042113 (2006); http://dx.doi.org/10.1063/1.2243799 (3 pages) | Cited 7 times

Online Publication Date: 27 July 2006

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A measurement of the mean e-h pair creation energy 〈Ee-h〉 in SiC using a scanning electron microscope is presented. Uncertainties stemming from backscattering from high Z metal contacts, as well as from the semiconductor surface, are removed by explicit measurement through direct electron bombardment of the bare semiconductor surface. A reduced value of 〈Ee-h〉 = 5.05 eV for 4H SiC is reported, which is significantly lower than previously reported values. Good correspondence with Monte Carlo simulations of impact ionization in 4H SiC was obtained.
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72.20.Ht High-field and nonlinear effects
61.82.Fk Semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Isotopic effect in deuterium-induced semiconductor surface metallization: D/3C–SiC(100) 3×2

J. Roy, V. Yu. Aristov, C. Radtke, P. Jaffrennou, H. Enriquez, P. Soukiassian, P. Moras, C. Spezzani, C. Crotti, and P. Perfetti

Appl. Phys. Lett. 89, 042114 (2006); http://dx.doi.org/10.1063/1.2243801 (3 pages) | Cited 7 times

Online Publication Date: 27 July 2006

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Atomic deuterium (D) interaction with the polar 3C–SiC(100) 3×2 surface is investigated by synchrotron radiation-based valence band and core level photoemission. D is found to induce metallization of the surface. The D atoms lead to a charge transfer into the topmost Si and C planes, with D atoms terminating top surface dangling bond and an asymmetric attack in the third Si plane. However, a significant isotopic effect is observed when compared to the H-induced metallization with amazingly smaller charge transfer suggesting dynamical effects.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.Hb Impurity and defect levels; energy states of adsorbed species
85.40.Ls Metallization, contacts, interconnects; device isolation
71.55.Ht Other nonmetals
81.65.-b Surface treatments

SiGe amorphization during Ge condensation in silicon germanium on insulator

S. Balakumar, G. Q. Lo, C. H. Tung, R. Kumar, N. Balasubramanian, D. L. Kwong, C. S. Ong, and M. F. Li

Appl. Phys. Lett. 89, 042115 (2006); http://dx.doi.org/10.1063/1.2222341 (3 pages) | Cited 9 times

Online Publication Date: 28 July 2006

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High temperature oxidation and annealing are found to be desirable to achieve a uniform germanium (Ge) profile in silicon germanium on insulator (SGOI) layers formed using germanium condensation technique. This work investigates the amorphization mechanism, which was considered as an undesirable consequence of lowering the temperature during Ge condensation when oxidations are conducted at 900 or 950 °C. A dual layer SGOI stack, composed of an amorphous layer above a crystalline layer, was obtained at low temperature condensation as characterized using transmission electron microscope and Auger analysis. A possible mechanism is presented. Si0.4Ge0.6OI and Si0.25Ge0.75OI layers can be achieved without amorphization through oxidation/annealing at 1050 °C and two oxidations at 1050 and 1000 °C, respectively.
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81.05.Hd Other semiconductors
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing
64.70.F- Liquid-vapor transitions
79.20.Fv Electron impact: Auger emission

Control of the spin Hall current in two dimensional electronic gas

T. O. Cheche and E. Barna

Appl. Phys. Lett. 89, 042116 (2006); http://dx.doi.org/10.1063/1.2234742 (3 pages) | Cited 3 times

Online Publication Date: 28 July 2006

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The intrinsic spin Hall conductivity is obtained for a two-dimensional electronic gas (2DEG) in the presence of strain, Rashba coupling, and an external in-plane applied magnetic field. The conduction electrons of [001] oriented quantum well are used to model the 2DEG. The spin current value is dependent on the stress applied in direction [111].
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72.25.Dc Spin polarized transport in semiconductors
73.21.Fg Quantum wells

Femtosecond pulse excited two-photon photoluminescence and second harmonic generation in ZnO nanowires

C. F. Zhang, Z. W. Dong, G. J. You, R. Y. Zhu, S. X. Qian, H. Deng, H. Cheng, and J. C. Wang

Appl. Phys. Lett. 89, 042117 (2006); http://dx.doi.org/10.1063/1.2236276 (3 pages) | Cited 34 times

Online Publication Date: 28 July 2006

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With femtosecond pulse excitation at the wavelength near 800 nm, we observed three upconverted emission peaks from ZnO nanowires. The ultraviolet peak at about 385 nm and the green emission band centered at about 515 nm were attributed to the near band edge emission and defect level emission, respectively, while the intermediate peak was assigned to the second harmonic generation. From the quadratic dependence of the emission intensity on the excitation pulse energy, it is confirmed that the 385 nm photoluminescence was mainly generated via two-photon absorption in ZnO nanowires under very intense light-matter interaction.
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78.67.Lt Quantum wires
78.47.-p Spectroscopy of solid state dynamics
78.55.Et II-VI semiconductors
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