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10 May 1999

Volume 74, Issue 19, pp. 2737-2895

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Critical built-in electric field for an optimum carrier collection in multiquantum well p-i-n diodes

I. Serdiukova, C. Monier, M. F. Vilela, and A. Freundlich

Appl. Phys. Lett. 74, 2812 (1999); http://dx.doi.org/10.1063/1.124022 (3 pages) | Cited 10 times

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The collection efficiency of carrier photogenerated in the intrinsic region of strained InAsxP1−x/InP multiquantum well p-i-n structures is analyzed. The existence of a critical threshold built-in electric field value above which total carrier collection becomes possible is demonstrated. Maximized carrier collection and high output voltage are systematically reached for built-in electric field exceeding the critical value while similar structures operating with a substantially lower built-in electric field (e.g., identical well characteristics but thicker i region) yields nonoptimized collection of carrier in this area and altered voltage output. The slight dependence of the critical electric field with the carrier confinement level is revealed, stressing out the importance of thermally activated escape energy. Finally, the results are discussed in the context of photovoltaic devices showing substantial efficiency improvement for devices designed with built-in electric fields in excess of the threshold value. © 1999 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.61.Ey III-V semiconductors
85.60.Dw Photodiodes; phototransistors; photoresistors
84.60.Jt Photoelectric conversion
73.50.Pz Photoconduction and photovoltaic effects

InAs/InGaAs quantum dot structures on GaAs substrates emitting at 1.3 μm

V. M. Ustinov, N. A. Maleev, A. E. Zhukov, A. R. Kovsh, A. Yu. Egorov, A. V. Lunev, B. V. Volovik, I. L. Krestnikov, Yu. G. Musikhin, N. A. Bert, P. S. Kop’ev, Zh. I. Alferov, N. N. Ledentsov, and D. Bimberg

Appl. Phys. Lett. 74, 2815 (1999); http://dx.doi.org/10.1063/1.124023 (3 pages) | Cited 164 times

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InAs self-organized quantum dots inserted in InGaAs quantum well have been grown on GaAs substrates by molecular beam epitaxy. The lateral size of the InAs islands has been found to be approximately 1.5 times larger as compared to the InAs/GaAs case, whereas the island heights and surface densities were close in both cases. The quantum dot emission wavelength can be controllably changed from 1.1 to 1.3 μm by varying the composition of the InGaAs quantum well matrix. Photoluminescence at 1.33 μm from vertical optical microcavities containing the InAs/InGaAs quantum dot array was demonstrated. © 1999 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Phonon-assisted capture and intradot Auger relaxation in quantum dots

R. Ferreira and G. Bastard

Appl. Phys. Lett. 74, 2818 (1999); http://dx.doi.org/10.1063/1.124024 (3 pages) | Cited 93 times

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We report on calculations of capture and relaxation of carriers in quantum dots, specifically, InAs/GaAs self-assembled dots. We point out that the phonon-assisted carrier capture presents strong resonances versus the dot size and that the intradot Auger relaxation is extremely fast in these structures. This shows that energy relaxation in InAs/GaAs self-organized quantum dots is dominated by capture effects. © 1999 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.55.Eq III-V semiconductors
63.20.K- Phonon interactions
71.38.-k Polarons and electron-phonon interactions

Nature and elimination of yellow-band luminescence and donor–acceptor emission of undoped GaN

G. Li, S. J. Chua, S. J. Xu, W. Wang, P. Li, B. Beaumont, and P. Gibart

Appl. Phys. Lett. 74, 2821 (1999); http://dx.doi.org/10.1063/1.124025 (3 pages) | Cited 36 times

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The nature of yellow-band luminescence (YL) and donor–acceptor (DA) emissions of undoped GaN grown on sapphire or laterally overgrown on patterned Si3N4 was investigated using low-temperature photoluminescence and spatially resolved photoluminescence. The states, producing the levels responsible for the YL and DA emissions, arise from complexes of extended defects and native-point defects (most likely Ga vacancies) or impurities (such as carbon). For GaN directly grown on a low-temperature-grown GaN buffer layer, the YL and DA emissions can be eliminated by simply increasing the buffer-layer growth temperature as the result of enlarging hexagonal crystallites, and consequently, reducing the density of extended defects. For laterally overgrown GaN, a much lower density of extended defects substantially suppresses the YL emission. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors
61.72.Nn Stacking faults and other planar or extended defects
61.72.J- Point defects and defect clusters

Nanometer-scale studies of vertical organization and evolution of stacked self-assembled InAs/GaAs quantum dots

B. Lita, R. S. Goldman, J. D. Phillips, and P. K. Bhattacharya

Appl. Phys. Lett. 74, 2824 (1999); http://dx.doi.org/10.1063/1.124026 (3 pages) | Cited 48 times

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We have investigated the vertical organization and evolution of 1-, 5-, 10-, and 20-layer stacks of molecular beam epitaxially grown self-assembled InAs/GaAs quantum dots using high resolution and large-scale cross-sectional scanning tunneling microscopy. We report results regarding the evolution of the dot sizes and shapes, and the assembly of vertically organized columns of stacked dots. As the number of dot layers within a stack is increased, the average spacing between vertically organized columns decreases, and the corresponding dots become more uniform in size. The data also suggest that the coalescence of neighboring stacks of dots has not occurred and therefore coalescence is not the mechanism leading to the observed uniform distribution of dot sizes and column spacings. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Stability investigation of cubic GaN films grown by metalorganic chemical vapor deposition on GaAs (001)

X. L. Sun, Hui Yang, L. X. Zheng, D. P. Xu, J. B. Li, Y. T. Wang, G. H. Li, and Z. G. Wang

Appl. Phys. Lett. 74, 2827 (1999); http://dx.doi.org/10.1063/1.124027 (3 pages) | Cited 14 times

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The thermal stability of cubic-phase GaN (c-GaN) films are investigated by photoluminescence (PL) and Raman scattering spectroscopy. C-GaN films are grown on GaAs (001) substrates by metalorganic chemical vapor deposition. PL measurements show that the near-band-edge emissions in the as-grown GaN layers and thermally treated samples are mainly from c-GaN. No degradation of the optical qualities is observed after thermal annealing. Raman scattering spectroscopy shows that the intensity of the E2 peak from hexagonal GaN grains increases with annealing temperature for the samples with poor crystal quality, while thermal annealing up to 1000 °C has no obvious effect on the samples with high crystal quality. © 1999 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Cc Kinetics of defect formation and annealing
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Deep levels in p-type InGaAsN lattice matched to GaAs

D. Kwon, R. J. Kaplar, S. A. Ringel, A. A. Allerman, Steven R. Kurtz, and E. D. Jones

Appl. Phys. Lett. 74, 2830 (1999); http://dx.doi.org/10.1063/1.124028 (3 pages) | Cited 45 times

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Deep-level transient spectroscopy measurements were utilized to investigate deep-level defects in metal–organic chemical vapor deposition-grown, unintentionally doped p-type InGaAsN films lattice matched to GaAs. The as-grown material displayed a high concentration of deep levels distributed within the band gap, with a dominant hole trap at Ev+0.10 eV. Postgrowth annealing simplified the deep-level spectra, enabling the identification of three distinct hole traps at 0.10, 0.23, and 0.48 eV above the valence-band edge, with concentrations of 3.5×1014, 3.8×1014, and 8.2×1014 cm−3, respectively. A direct comparison between the as-grown and annealed spectra revealed the presence of an additional midgap hole trap, with a concentration of 4×1014 cm−3 in the as-grown material. The concentration of this trap is sharply reduced by annealing, which correlates with improved material quality and minority-carrier properties after annealing. Of the four hole traps detected, only the 0.48 eV level is not influenced by annealing, suggesting this level may be important for processed InGaAsN devices in the future. © 1999 American Institute of Physics.
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71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.72.Cc Kinetics of defect formation and annealing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors

Deposition of passivated gold nanoclusters onto prepatterned substrates

A. J. Parker, P. A. Childs, R. E. Palmer, and M. Brust

Appl. Phys. Lett. 74, 2833 (1999); http://dx.doi.org/10.1063/1.124029 (3 pages) | Cited 13 times

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Gold nanoclusters, chemically passivated with decanethiol, have been deposited from solution onto silicon dioxide surfaces prepatterned by photolithography. After lift-off of the photoresist, preferential cluster accumulation is observed along the edges of the resist structures. Elsewhere on the hydrophilic surface, islands of clusters are observed. By contrast, HF treatment, creating a hydrophobic surface, leads to wetting of the unmasked regions of the substrate by the passivated clusters. © 1999 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Bx Metals, semimetals, and alloys
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.-a Thin film structure and morphology
85.40.Hp Lithography, masks and pattern transfer
81.65.Rv Passivation

Epitaxial lateral overgrowth of GaN over AlOx surface formed on Si substrate

Nobuhiko P. Kobayashi, Junko T. Kobayashi, Xingang Zhang, P. Daniel Dapkus, and Daniel H. Rich

Appl. Phys. Lett. 74, 2836 (1999); http://dx.doi.org/10.1063/1.124030 (3 pages) | Cited 26 times

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An approach by which single crystal α-GaN can be grown laterally over oxidized AlAs (AlOx) formed on Si substrates is demonstrated. Regular α-Ga2-O3 stripe templates, spatially separated by AlOx, on which subsequent GaN growth is selectively seeded are formed. Since the boundary between the stripe template and AlOx is nominally planar, two pyramidal planes on separated GaN can merge by growing laterally over the AlOx (referred to as planar epitaxial lateral overgrowth). Transmission electron microscopy reveals that the number of structural defects in GaN laterally grown over the AlOx is remarkably reduced compared to that in GaN grown on the stripe templates, and accordingly cathodoluminescence reveals a strong band edge emission from GaN laterally grown over the AlOx, suggesting that this approach allows us to grow GaN on Si substrates with fewer defects. © 1999 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.60.Hk Cathodoluminescence, ionoluminescence
81.05.Ea III-V semiconductors
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Strain and oxygenation effects on superconductivity of La1.85Sr0.15CuO4 thin films

Weidong Si, Hong-Cheng Li, and X. X. Xi

Appl. Phys. Lett. 74, 2839 (1999); http://dx.doi.org/10.1063/1.124031 (3 pages) | Cited 28 times

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We have measured normal-state and superconducting properties of La1.85Sr0.15CuO4 thin films as a function of lattice strain and oxygen content. Strain was controlled by depositing SrLaAlO4 buffer layers of different thickness on SrTiO3 substrates, and an ozone/molecular oxygen mixture was used during cooling to achieve better oxygen uptake. We found that both full oxygenation and compressive in-plane strain are critical for the properties of the La1.85Sr0.15CuO4 thin films, and they are closely correlated. © 1999 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
61.66.Bi Elemental solids
61.66.Dk Alloys
68.60.Bs Mechanical and acoustical properties

Preparation of rare-earth manganite-oxide thin films by metalorganic aerosol deposition technique

V. Moshnyaga, I. Khoroshun, A. Sidorenko, P. Petrenko, A. Weidinger, M. Zeitler, B. Rauschenbach, R. Tidecks, and K. Samwer

Appl. Phys. Lett. 74, 2842 (1999); http://dx.doi.org/10.1063/1.124032 (3 pages) | Cited 35 times

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A chemical deposition technique based on the use of solutions of metal-chelate coordination compounds has been applied to prepare rare-earth–manganite-oxide thin films. La0.67Ca0.33MnO3 and La0.67Sr0.33MnO3 thin films have been grown epitaxially on MgO(100) substrates and characterized by structural (x-ray diffraction analysis, atomic force microscopy) and magnetotransport (T = 4.2–300 K, and B = 0–5 T) measurements. © 1999 American Institute of Physics.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
75.70.Ak Magnetic properties of monolayers and thin films
75.47.Gk Colossal magnetoresistance
68.55.-a Thin film structure and morphology
72.60.+g Mixed conductivity and conductivity transitions
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ng Insulators
75.50.Dd Nonmetallic ferromagnetic materials

Spin-polarized current in semimagnetic semiconductor heterostructures

V. A. Chitta, M. Z. Maialle, S. A. Leão, and M. H. Degani

Appl. Phys. Lett. 74, 2845 (1999); http://dx.doi.org/10.1063/1.124033 (3 pages) | Cited 9 times

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A semimagnetic semiconductor tunneling device is proposed as a spin filter. This device, which gives spin-polarized electron current, is obtained by choosing different layers of II-VI compounds, with magnetic moments of substitutional ions of Mn2+ in some of the layers. We present a theoretical calculation of the tunneling current for the device, in which electron spin-flip scattering produced by the thermal fluctuations of the magnetic moments is accounted for and found to be inefficient in depolarizing the current. A different system is also investigated to show more clearly the effects of spin-flip scattering on the tunneling current. © 1999 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Pp Magnetic semiconductors
75.45.+j Macroscopic quantum phenomena in magnetic systems
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
75.20.Hr Local moment in compounds and alloys; Kondo effect, valence fluctuations, heavy fermions
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In situ x-ray diffraction study of an electric field induced phase transition in the single crystal relaxor ferroelectric, 92% Pb(Zn1/3Nb2/3)O3–8% PbTiO3

M. K. Durbin, E. W. Jacobs, J. C. Hicks, and S.-E. Park

Appl. Phys. Lett. 74, 2848 (1999); http://dx.doi.org/10.1063/1.124034 (3 pages) | Cited 77 times

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We have used in situ x-ray diffraction to measure strain curves of single crystals of 92% Pb(Zn1/3Nb2/3)O3–8% PbTiO3 poled in the 〈001〉 direction. We observed shifts in the (002) and (330) peaks as functions of applied voltage (in the 〈001〉 direction), thereby measuring the crystallographic strain. Our measurements confirm that the high strains observed using macroscopic methods reflect microscopic strains in the crystal lattice. By watching the disappearance of a rhombohedral splitting in the (330) peak, we also find direct evidence that the field-induced phase transition reported by S.-E. Park and T. R. Shrout [J. Appl. Phys. 82, 1804 (1997)] occurs between a pseudorhombohedral and tetragonal crystal structure. © 1999 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
62.20.-x Mechanical properties of solids

Abrupt PbTiO3/SrTiO3 superlattices grown by reactive molecular beam epitaxy

J. C. Jiang, X. Q. Pan, W. Tian, C. D. Theis, and D. G. Schlom

Appl. Phys. Lett. 74, 2851 (1999); http://dx.doi.org/10.1063/1.124035 (3 pages) | Cited 63 times

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PbTiO3/SrTiO3 superlattices were grown on (001) SrTiO3 substrates by reactive molecular beam epitaxy (MBE). Sharp superlattice reflections were observed by x-ray diffraction. High-resolution transmission electron microscopy of a [(PbTiO3)10/(SrTiO3)10]15 superlattice revealed that the PbTiO3/SrTiO3 interface structure is atomically sharp. The superlattice interfaces are fully coherent; no misfit dislocations or other crystal defects were observed in the superlattice by transmission electron microscopy. Selected area electron diffraction patterns indicated that the PbTiO3 layers are oriented with the c axis parallel to the growth direction. The dimensional control and interface abruptness achieved in this model system indicate that MBE is a viable method for constructing oxide multilayers on a scale where enhanced dielectric effects are expected. © 1999 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Ct Interface structure and roughness
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity

Electrical properties of hafnium silicate gate dielectrics deposited directly on silicon

G. D. Wilk and R. M. Wallace

Appl. Phys. Lett. 74, 2854 (1999); http://dx.doi.org/10.1063/1.124036 (3 pages) | Cited 17 times

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Hafnium silicate (HfSixOy) gate dielectric films with ∼6 at. % Hf exhibit significantly improved leakage properties over SiO2 in the ultrathin regime while remaining thermally stable in direct contact with Si. Capacitance–voltage measurements show an equivalent oxide thickness (tox) of less than 18 Å for a 50 Å HfSixOy film deposited directly on a Si substrate, with no significant dispersion of the capacitance for frequencies ranging from 10 kHz to 1 MHz. Current–voltage measurements show for the same film a leakage current of 1.2×10−6 A/cm2 at 1 V bias. Hysteresis in these films is measured to be less than 20 mV, the breakdown field is measured to be EBD ∼ 10 MV/cm, and the midgap interface state density is Dit ∼ 1011 cm−2 eV−1. Cross-sectional transmission electron microscopy shows no signs of reaction or crystallization in HfSixOy films on Si after being annealed at 800 °C for 30 min. © 1999 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.55.-g Dielectric thin films
77.22.Jp Dielectric breakdown and space-charge effects
73.20.At Surface states, band structure, electron density of states
61.72.Cc Kinetics of defect formation and annealing

Improved properties of La2/3Ca1/3MnO3 thin films by addition of silver

R. Shreekala, M. Rajeswari, S. P. Pai, S. E. Lofland, V. Smolyaninova, K. Ghosh, S. B. Ogale, S. M. Bhagat, M. J. Downes, R. L. Greene, R. Ramesh, and T. Venkatesan

Appl. Phys. Lett. 74, 2857 (1999); http://dx.doi.org/10.1063/1.124037 (3 pages) | Cited 48 times

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Thin films of Ag-added La2/3Ca1/3MnO3 exhibit enhancement of several desirable characteristics over the pristine counterparts. We find that the addition of Ag results in a pronounced increase in the insulator–metal transition temperature (Tp) and ferromagnetic transition temperature (Tc). There is also a remarkable improvement in the magnetic and electrical homogeneity of the samples as indicated by narrower ferromagnetic resonance linewidths and narrower resistive transitions, respectively. The observed improvement in properties is inferred to be largely associated with improved oxygen stoichiometry of the films although microstructural effects are not ruled out. © 1999 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
72.60.+g Mixed conductivity and conductivity transitions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
61.66.Bi Elemental solids
61.66.Dk Alloys
75.47.Gk Colossal magnetoresistance
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
73.61.Ng Insulators
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Multilayer stacked electroluminescent devices

W. Park, T. C. Jones, B. K. Wagner, and C. J. Summers

Appl. Phys. Lett. 74, 2860 (1999); http://dx.doi.org/10.1063/1.124038 (3 pages)

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A device concept, the multilayer stacked electroluminescent device is presented. This device consists of a series of double insulating-layer electroluminescent units stacked up on top of one another, separated by transparent electrodes and alternately biased in opposite directions. This unique design allows independent control of the drive voltage and the total phosphor thickness. The drive voltage depends only on the individual phosphor layer thickness while the total phosphor thickness, and thus the total brightness, can be increased by increasing the number of layers. The anticipated enhancement in brightness was predicted by equivalent circuit analysis and demonstrated by prototype devices fabricated by atomic layer epitaxy. © 1999 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems
78.60.Fi Electroluminescence
78.66.Nk Insulators

Magnetic detection of photogenerated currents in semiconductor wafers using superconducting quantum interference devices

J. Beyer, H. Matz, D. Drung, and Th. Schurig

Appl. Phys. Lett. 74, 2863 (1999); http://dx.doi.org/10.1063/1.124039 (3 pages) | Cited 13 times

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A completely noninvasive method is presented for the investigation of semiconductor wafers with high spatial resolution utilizing a superconducting quantum interference device (SQUID) magnetometer system. The method is based on the detection of the magnetic field caused by photocurrents generated in the semiconductor sample using a sensitive SQUID magnetometer. The photocurrents arise when laser light with a photon energy exceeding the band gap of the semiconductor is focused onto the sample surface in a region of a doping gradient. The spatial resolution of this detection method is mainly determined by the size of the excitation focus of about 20 μm. We report on measurements of silicon wafers with small growth-related doping fluctuations. © 1999 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
07.55.Ge Magnetometers for magnetic field measurements
81.70.Jb Chemical composition analysis, chemical depth and dopant profiling
81.05.Cy Elemental semiconductors
72.40.+w Photoconduction and photovoltaic effects

Application of nonalloyed PdGe ohmic contact to self-aligned gate AlGaAs/InGaAs pseudomorphic high-electron-mobility transistor

Jung-Woo Oh and Jong-Lam Lee

Appl. Phys. Lett. 74, 2866 (1999); http://dx.doi.org/10.1063/1.124040 (3 pages)

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A self-aligned gate pseudomorphic high-electron-mobility transistor (PHEMT) was developed through nonalloyed PdGe ohmic contact on an n+-GaAs cap layer. The lowest contact resistivity obtained was 1.2×10−7 Ω cm2 at 300 °C. This allows us to change the sequence on the formation of source/drain and gate electrodes in the process of PHEMT fabrication, namely self-aligned gate PHEMT. Performance of the self-aligned gate PHEMT was remarkably pronounced with annealing temperature or the decrease of contact resistivity. This is due to the solid-phase regrowth of highly Ge-doped GaAs below the PdGe contact, which acts to reduce barrier height for electron tunneling. © 1999 American Institute of Physics.
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85.30.Tv Field effect devices
73.40.Ns Metal-nonmetal contacts
85.40.Ls Metallization, contacts, interconnects; device isolation
61.72.Cc Kinetics of defect formation and annealing
73.40.Cg Contact resistance, contact potential

An ohmic nanocontact to GaAs

Takhee Lee, Jia Liu, D. B. Janes, V. R. Kolagunta, J. Dicke, R. P. Andres, J. Lauterbach, M. R. Melloch, D. McInturff, J. M. Woodall, and R. Reifenberger

Appl. Phys. Lett. 74, 2869 (1999); http://dx.doi.org/10.1063/1.124041 (3 pages) | Cited 14 times

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The formation and characterization of nanometer-size, ohmic contacts to n-type GaAs substrates are described. The nanocontacts are formed between a single-crystalline, nanometer-size Au cluster and a GaAs structure capped with layer of low-temperature-grown GaAs (LTG:GaAs). An organic monolayer of xylyl dithiol (p-xylene-α,α′- dithiol; C8H10S2) provides mechanical and electronic tethering of the Au cluster to the LTG:GaAs surface. The I(V) data of the Au cluster/xylyl dithiol/GaAs show ohmic contact behavior with good repeatability between various clusters distributed across the surface. The specific contact resistance is determined to be 1×10−6 Ω cm2. Current densities above 1×106 A/cm2 have been observed. © 1999 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

A traveling-wave THz photomixer based on angle-tuned phase matching

Shuji Matsuura, Geoffrey A. Blake, Rolf A. Wyss, J. C. Pearson, Christoph Kadow, Andrew W. Jackson, and Arthur C. Gossard

Appl. Phys. Lett. 74, 2872 (1999); http://dx.doi.org/10.1063/1.124042 (3 pages) | Cited 41 times

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A traveling-wave THz photomixer based on a free-space optical-THz phase-matching scheme is proposed. A dc-biased coplanar strip line fabricated on low-temperature-grown GaAs serves as the active area of the device, and is illuminated by two noncollinear laser beams which generate interference fringes that are accompanied by THz waves. The device with the laser-power-handling capability over 300 mW and a 3-dB bandwidth of 1.8 THz was experimentally demonstrated. The results show that traveling-wave photomixers have the potential to surpass small-area designs. © 1999 American Institute of Physics.
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85.60.-q Optoelectronic devices
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
84.40.Az Waveguides, transmission lines, striplines
42.79.Nv Optical frequency converters
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.25.Hz Interference

Experimental demonstration of a binary wire for quantum-dot cellular automata

A. O. Orlov, I. Amlani, G. Toth, C. S. Lent, G. H. Bernstein, and G. L. Snider

Appl. Phys. Lett. 74, 2875 (1999); http://dx.doi.org/10.1063/1.124043 (3 pages) | Cited 30 times

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Experimental studies are presented of a binary wire based on the quantum-dot cellular automata computational paradigm. The binary wire consists of capacitively coupled double-dot cells charged with single electrons. The polarization switch caused by an applied input signal in one cell leads to the change in polarization of the adjacent cell and so on down the line, as in falling dominos. Wire polarization was measured using single islands as electrometers. Experimental results are in very good agreement with the theory and confirm there are no metastable states in the wire. © 1999 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.61.At Metal and metallic alloys
03.67.Lx Quantum computation architectures and implementations

A magnetostatic forward volume wave oscillator-based magneto-optic Bragg cell modulator

Jun Su and Chen S. Tsai

Appl. Phys. Lett. 74, 2878 (1999); http://dx.doi.org/10.1063/1.124044 (3 pages) | Cited 3 times

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A guided-wave magneto-optic (MO) Bragg cell modulator that utilizes a magnetostatic forward volume wave (MSFVW) oscillator through a feedback loop is reported. The carrier frequency of the MSFVW signals involved in the MO interaction is tuned linearly from 2.112 to 3.274 GHz by increasing an external bias magnetic field from 2350 to 2900 Oe. Compared with a conventional delay line-based MO Bragg cell modulator, the oscillator-based MO modulator can provide higher diffraction efficiency by twofold to fourfold owing to reduction of insertion losses in the MSFVW oscillator. Furthermore, such oscillator-type MO modulator can be more easily integrated with other monolithic microwave integrated circuit components. © 1999 American Institute of Physics.
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85.70.Sq Magnetooptical devices
42.79.Hp Optical processors, correlators, and modulators
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices

Towards background-limited, room-temperature, infrared photon detectors in the 3–13 μm wavelength range

C. T. Elliott, N. T. Gordon, and A. M. White

Appl. Phys. Lett. 74, 2881 (1999); http://dx.doi.org/10.1063/1.124045 (3 pages) | Cited 19 times

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We have analyzed the various noise processes occurring in photon infrared detectors operating at room temperature and show that background-limited performance for photon detectors is potentially achievable at room temperature over the 3–13 μm band even in restricted fields of view. We discuss practical embodiments in which this might be realized and give quantitative estimates of the material properties required to achieve this performance. A critical feature to achieve the highest performance is that devices within an array should not be radiatively coupled to each other. © 1999 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

A cryogenic amplifier for direct measurement of high-frequency signals from a single-electron transistor

S. L. Pohlen, R. J. Fitzgerald, J. M. Hergenrother, and M. Tinkham

Appl. Phys. Lett. 74, 2884 (1999); http://dx.doi.org/10.1063/1.124046 (3 pages) | Cited 4 times

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We have developed a cryogenic voltage amplifier using GaAs metal semiconductor field effect transistors and coupled it to a superconducting single-electron transistor (SET) inside a dilution refrigerator. With this amplifier, we could extend the maximum output frequency of the SET, normally less than a kilohertz, up to 1 MHz. By placing this amplifier off-chip, we could maintain the low SET temperature required for proper SET operation. © 1999 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
85.30.Tv Field effect devices
84.30.Le Amplifiers
07.68.+m Photography, photographic instruments; xerography
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
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