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20 Dec 1999

Volume 75, Issue 25, pp. 3905-4030

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Ohmic contact to p-type GaAs using Cu3Ge

M. O. Aboelfotoh, M. A. Borek, and J. Narayan

Appl. Phys. Lett. 75, 3953 (1999); http://dx.doi.org/10.1063/1.125505 (3 pages) | Cited 10 times

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We have investigated ε1−Cu3Ge as an ohmic contact to p-type GaAs, and found that the ε1−Cu3Ge contact has a specific contact resistivity of 5×10−6 Ω cm2 on p-type GaAs with doping concentrations of ∼ 7×1018 cm−3. The ε1−Cu3Ge contact exhibits a planar and structurally abrupt interface with the GaAs, and no reaction between the contact metal and the GaAs is required for contact formation. The contact is electrically stable during annealing at temperatures up to 400 °C. It is suggested that Ge is incorporated into the GaAs as a p-type impurity resulting in a low contact resistivity. Furthermore, the addition of Ge to Cu to form ε1−Cu3Ge is found to impede the diffusion of Cu into the p-type GaAs. Along with the results reported for n-type GaAs, the present results indicate that ε1−Cu3Ge is an attractive candidate for ohmic contact formation on both n- and p-type GaAs. © 1999 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
85.40.Ls Metallization, contacts, interconnects; device isolation
73.40.Cg Contact resistance, contact potential
68.35.Ct Interface structure and roughness
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing

Tantalum carbide ohmic contacts to n-type silicon carbide

T. Jang, L. M. Porter, G. W. M. Rutsch, and B. Odekirk

Appl. Phys. Lett. 75, 3956 (1999); http://dx.doi.org/10.1063/1.125506 (3 pages) | Cited 13 times

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Tantalum carbide contacts with and without Au, Pt, and W/WC overlayers on n-type 6H–SiC (0001) were ohmic after annealing at temperatures between 800 and 1075 °C. Specific contact resistivities (SCRs) were calculated from current–voltage measurements of transmission line model patterns at temperatures ranging from 20 to 400 °C in air. The minimum SCRs at room temperature on SiC (2.3×1019 cm−3) for TaC and for TaC with Pt and Au overlayers were 2.1×10−5, 7.4×10−6, and 1.4×10−6 Ω cm2, respectively. The SCRs for both the Au/TaC/SiC (5.3×10−7Ω cm2) and the Pt/TaC/SiC (7.5×10−7 Ω cm2) samples decreased with measurement temperature to 200 and 400 °C, respectively, while the latter samples showed reversibility after heating to 400 °C. W/WC/TaC/SiC samples showed the best stability after annealing at 400 °C for 144 h in vacuum. Changes in the electrical characteristics were correlated with increases in O incorporation in the contacts as a result of annealing. Investigation of the TaC/SiC interface by transmission electron microscopy indicated that there was little or no reaction between the materials. © 1999 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.Ct Interface structure and roughness
61.72.Cc Kinetics of defect formation and annealing
68.60.Dv Thermal stability; thermal effects

THz emission from coherently controlled photocurrents in GaAs

D. Côté, J. M. Fraser, M. DeCamp, P. H. Bucksbaum, and H. M. van Driel

Appl. Phys. Lett. 75, 3959 (1999); http://dx.doi.org/10.1063/1.125531 (3 pages) | Cited 21 times

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We report broadband terahertz radiation from ballistic photocurrents generated via quantum interference of one- and two-photon absorption in low-temperature-grown and semi-insulating GaAs at 295 K. For 90 fs, 1550 and 775 nm optical pulses, we obtain phase-controllable near-single cycle 4 THz radiation. Higher frequency THz emission should be achievable with shorter pulses. At a 250 kHz repetition rate and average powers of 10 mW (1550 nm) and 400 μW (775 nm), we measure 3 nW of THz power, limited mainly by phase walkoff of the optical beams within the 1.5-μm-thick sample and collection efficiency. © 1999 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
72.80.Ey III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
72.20.Ht High-field and nonlinear effects
73.23.-b Electronic transport in mesoscopic systems

Diminished photoluminescence polarization due to exciton ionization in strained Si1−xGex/Si(001) quantum wells

T. Miyazaki and S. Fukatsu

Appl. Phys. Lett. 75, 3962 (1999); http://dx.doi.org/10.1063/1.125507 (3 pages) | Cited 2 times

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The photoluminescence (PL) of strained Si1−xGex/Si(001) quantum wells was measured in an edge-emitting configuration. The no-phonon PL was found to be polarized largely along the quantum-well plane at low temperature, whereas such in-plane polarization was diminished as the sample temperature was increased. Exciton dissociation occurring at higher temperature is responsible for the diminution of PL polarization, which is consistent with an analogous reduction of in-plane polarization due to field ionization of excitons. © 1999 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Li Other semiconductors
71.35.Gg Exciton-mediated interactions
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Shear piezoelectric coefficients of gallium nitride and aluminum nitride

S. Muensit, E. M. Goldys, and I. L. Guy

Appl. Phys. Lett. 75, 3965 (1999); http://dx.doi.org/10.1063/1.125508 (3 pages) | Cited 24 times

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We have developed a direct method of measuring the shear strain using a laser-based interferometer. The method was applied to the measurement of the d15 coefficient for wurtzite GaN and AlN. A value for d15 of 3.6±0.2 pm V−1 for AlN has been obtained, in good agreement with values quoted in the literature. The value of d15 for GaN has also been measured to be 3.1±0.2 pm V−1. © 1999 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.65.Bn Piezoelectric and electrostrictive constants
07.60.Ly Interferometers
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Influence of a thin AlAs cap layer on optical properties of self-assembled InAs/GaAs quantum dots

M. Arzberger, U. Käsberger, G. Böhm, and G. Abstreiter

Appl. Phys. Lett. 75, 3968 (1999); http://dx.doi.org/10.1063/1.125509 (3 pages) | Cited 46 times

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The influence of an AlAs cap layer with a thickness of a few monolayers on the optical properties of molecular beam epitaxy-grown InAs/GaAs self-assembled quantum dots is investigated. The capping of the InAs islands with a thin AlAs layer before the overgrowth by GaAs leads to a blueshift of the photoluminescence at a substrate temperature TS = 480 °C, but to a significant redshift at TS = 530 °C. This indicates that the InAs/GaAs intermixing caused by In segregation at TS = 530 °C can be considerably reduced by a thin AlAs capping layer. This leads to deeper potential wells due to the higher In content in the quantum dots which results in a room-temperature photoluminescence at about 1.3 μm. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Fx Diffusion; interface formation
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors

Defect-related local-electric-field impact on p–n junction parameters

A. Czerwinski

Appl. Phys. Lett. 75, 3971 (1999); http://dx.doi.org/10.1063/1.125510 (3 pages) | Cited 7 times

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A method is proposed to accurately determine the electric-field impact on a p–n junction. The generation current component is separated from the total leakage current, with correction for the reverse-bias-dependent diffusion current. The sources of the electric-field enhancement are considered. The type of the dominant center, its distribution and energy, the local electric field due to imperfections, and the mechanical stress are determined. © 1999 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.55.Cn Elemental semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Biexciton photoluminescence in cubic ZnS single crystals

Nguyen Quang Liem, Vu Xuan Quang, Do Xuan Thanh, Joo In Lee, Annamraju Kasi Viswanath, and Dongho Kim

Appl. Phys. Lett. 75, 3974 (1999); http://dx.doi.org/10.1063/1.125511 (3 pages) | Cited 2 times

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The near-band-edge emission of cubic zinc sulfide single crystals has been studied in detail by steady-state photoluminescence (PL) and time-resolved photoluminescence. Based on the peak energy positions, excitation power density and temperature dependencies of the PL spectra, we interpret the emission as recombination of the free and bound excitons and of the biexcitons. We observed the biexciton emission at 3.791 eV in cubic ZnS single crystals with very low excitation power density. Its binding energy and radiative lifetime were determined to be about 9 meV and 52 ps at 12 K, respectively. © 1999 American Institute of Physics.
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78.55.Et II-VI semiconductors
71.35.-y Excitons and related phenomena
78.47.-p Spectroscopy of solid state dynamics

Growth of Si/3C–SiC/Si(100) heterostructures by pulsed supersonic free jets

Y. Ikoma, T. Endo, F. Watanabe, and T. Motooka

Appl. Phys. Lett. 75, 3977 (1999); http://dx.doi.org/10.1063/1.125512 (3 pages) | Cited 11 times

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We have investigated the epitaxial growth of multilayer structures of Si/3C–SiC/Si(100) by pulsed supersonic free jets of methylsilane (CH3SiH3) for SiC growth and trisilane (Si3H8) for Si growth. Epitaxial Si layers were obtained only on very thin ( ≈ 3 nm) 3C–SiC epitaxial layers, while polycrystalline Si was grown on thicker 3C–SiC layers. It was also found that the transition regions with a thickness of ≈ 1 nm existed at the interface between epitaxial 3C–SiC and Si layers by high-resolution transmission electron microscopy observation. These results suggest that the surface roughness and thickness of the 3C–SiC layer play an important role for epitaxial growth of Si. © 1999 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
68.35.Ct Interface structure and roughness
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Cy Elemental semiconductors
81.05.Hd Other semiconductors

Temperature- and oxygen partial pressure-dependent electrical conductivity in nanoporous rutile and anatase

Th. Dittrich, J. Weidmann, F. Koch, I. Uhlendorf, and I. Lauermann

Appl. Phys. Lett. 75, 3980 (1999); http://dx.doi.org/10.1063/1.125513 (3 pages) | Cited 30 times

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The dependence of the electrical conductivity (σ) of sintered nanoporous TiO2 (rutile and anatase) layers on temperature (T) and partial pressure of oxygen (pO2) has been studied by impedance spectroscopy for T up to 450 °C and pO2 up to 10−5 mbar. The diameter of the TiO2 nanoparticles was changed between 5 and 60 nm. σ is thermally activated with EA = 0.85 eV independent of the absolute value of σ and depends on pO2 by power law for pO2<1–10 mbar. The electrical properties of reduced nanoporous TiO2 are determined by surface chemical reactions which lead to the formation of shallow donor and deep trap states. © 1999 American Institute of Physics.
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72.20.-i Conductivity phenomena in semiconductors and insulators
72.80.Ga Transition-metal compounds
71.55.Ht Other nonmetals
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Detection of Cr impurities in GaN by room temperature cathodoluminescence spectroscopy

M. Toth and M. R. Phillips

Appl. Phys. Lett. 75, 3983 (1999); http://dx.doi.org/10.1063/1.125528 (3 pages) | Cited 7 times

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Trace levels of Cr impurities in epitaxial GaN grown on sapphire substrates were investigated using cathodoluminescence (CL) spectroscopy. CL emissions characteristic of Cr in an octahedral crystal field were observed from β−Ga2O3 overlayers produced on GaN by post-growth thermal annealing in dry O2. Cr luminescence was also observed from the sapphire substrates, a likely source of the Cr contaminant. The presented results illustrate the use of β−Ga2O3 overlayers as high sensitivity indicators of the presence of Cr in GaN. © 1999 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
78.60.Hk Cathodoluminescence, ionoluminescence
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
78.66.Fd III-V semiconductors
71.70.Ch Crystal and ligand fields
61.72.Cc Kinetics of defect formation and annealing

Air-bridge-structured silicon nanowire and anomalous conductivity

Hideo Fujii, Seigo Kanemaru, Takashi Matsukawa, and Junji Itoh

Appl. Phys. Lett. 75, 3986 (1999); http://dx.doi.org/10.1063/1.125514 (3 pages) | Cited 16 times

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An air-bridge-structured silicon nanowire was made by micromachining a silicon-on-insulator (SOI) substrate and electrically characterized. The nanowire was isolated from the substrate by an air gap and typically 20–100 nm in diameter and 300–600 nm in length. Current–voltage characteristics of these wires were anomalous electric conductivity such as negative resistance and hysteresis at room temperature. Charge accumulation into surface states is considered a dominant characteristic. © 1999 American Institute of Physics.
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73.61.Cw Elemental semiconductors
73.50.Fq High-field and nonlinear effects
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Cy Elemental semiconductors
73.20.At Surface states, band structure, electron density of states

Room-temperature electroluminescence from erbium-doped porous silicon

Herman A. Lopez and Philippe M. Fauchet

Appl. Phys. Lett. 75, 3989 (1999); http://dx.doi.org/10.1063/1.125515 (3 pages) | Cited 17 times

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We demonstrate stable room-temperature electroluminescence (EL) at 1.54 μm from erbium-doped porous silicon devices under both forward- and reverse-bias conditions. Erbium was infiltrated in the pores ( ⩽ 1019 cm−3) by cathodic electrochemical migration of the ions followed by high-temperature annealing (950–1100 °C) in an oxygen and nitrogen environment. The devices exhibit an exponential EL dependence in both bias conditions as a function of input power. In reverse bias, the external quantum efficiency reaches 0.01%. The EL intensity decreases by a factor of 24 for reverse bias and 2.6 for forward bias when the temperature increases from 240 to 300 K. The different device characteristics in forward and reverse biases suggest that different excitation mechanisms are responsible for EL. © 1999 American Institute of Physics.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
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