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17 Nov 2003

Volume 83, Issue 20, pp. 4083-4258

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Appl. Phys. Lett. 83, 4238 (2003); http://dx.doi.org/10.1063/1.1627935 (3 pages)

H. B. Peng, T. G. Ristroph, G. M. Schurmann, G. M. King, J. Yoon, V. Narayanamurti, and J. A. Golovchenko
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Effects of surface treatments on isolation currents in AlGaN/GaN high-electron-mobility transistors

N. A. Moser, J. K. Gillespie, G. D. Via, A. Crespo, M. J. Yannuzzi, G. H. Jessen, R. C. Fitch, B. Luo, F. Ren, B. P. Gila, A. H. Onstine, C. R. Abernathy, and S. J. Pearton

Appl. Phys. Lett. 83, 4178 (2003); http://dx.doi.org/10.1063/1.1628394 (3 pages) | Cited 8 times

Online Publication Date: 12 November 2003

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Interdevice isolation currents in mesa-isolated AlGaN/GaN high-electron-mobility transistors are found to exhibit thermally activated behavior, with an activation energy of ∼ 1.5 eV. This value is largely independent of surface cleaning processes or the type of passivation film (SiNX, Sc2O3, MgO) used to reduce the current collapse phenomena in the devices. However, the magnitude of the isolation current is a strong function of the surface treatment employed. The lowest isolation currents for conditions under which current collapse is mitigated are obtained using Sc2O3 passivation layers. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
68.47.Fg Semiconductor surfaces
81.65.Rv Passivation
81.65.Cf Surface cleaning, etching, patterning
73.20.At Surface states, band structure, electron density of states

Temperature dependence of the c-axis mobility in 6H-SiC Schottky diodes

F. Roccaforte, F. La Via, V. Raineri, F. Mangano, and L. Calcagno

Appl. Phys. Lett. 83, 4181 (2003); http://dx.doi.org/10.1063/1.1628390 (3 pages) | Cited 10 times

Online Publication Date: 12 November 2003

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In this work, the temperature dependence of the mobility along the c axis in silicon carbide (6H-SiC) was determined from the I–V characteristics of Schottky diodes. This procedure used series resistance measurements with Norde’s method in Schottky diodes for extracting the mobility values in the epitaxial layer. For a dopant concentration of 3×1015 cm−3, at room temperature a value of 61 cm2 V−1 s−1 was found, which decreased to 24 cm2 V−1 s−1 at 448 K. In the temperature range 298–448 K, a dependence of the mobility as T−2.1 was determined. This result suggests that the lattice scattering, together with other mechanisms such as scattering with defects in the material, rule the carrier transport in this temperature range. © 2003 American Institute of Physics.
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85.30.Hi Surface barrier, boundary, and point contact devices
73.30.+y Surface double layers, Schottky barriers, and work functions
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Le Other inorganic semiconductors
85.30.Kk Junction diodes

Thermal conductivity in strain symmetrized Si/Ge superlattices on Si(111)

S. Chakraborty, C. A. Kleint, A. Heinrich, C. M. Schneider, J. Schumann, M. Falke, and S. Teichert

Appl. Phys. Lett. 83, 4184 (2003); http://dx.doi.org/10.1063/1.1628819 (3 pages) | Cited 16 times

Online Publication Date: 12 November 2003

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We have presented systematic cross-plane thermal conductivity (λ) data for the undoped strain-symmetrized Si/Ge superlattices grown on Si(111) with superlattice (SL) period thickness varying from 3.6 to 16 nm. In thin SL period (L ⩽ 7 nm) samples, the data have shown considerable reductions of λ, by more than 50% and 30% compared to the SiGe alloy and to the earlier reported values in (100)-oriented Si/Ge superlattice structures (SLS), respectively. For the thick SL period samples (L>10 nm), λ has shown a tendency to saturate at the SiGe alloy value. This is understood as, with increasing L, the SLS breaks and the SiGe alloying starts to grow. This structural behavior is clearly observed in the cross-plane transmission electron microscope images as well. In addition to these, for the thin SL period (L ⩽ 7 nm) samples, the data have shown a shallow minimum which is attributed to the competing behavior of the wave nature and the classical particle nature of the localized phonons. Nevertheless, the present study of thermal conductivity on undoped strain-symmetrized Si/Ge SLs in (111) orientation suggests that an enhancement of thermoelectric figure-of-merit Z is possible. © 2003 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
73.50.Lw Thermoelectric effects
72.20.Pa Thermoelectric and thermomagnetic effects
68.65.Cd Superlattices
68.60.Dv Thermal stability; thermal effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Low and anisotropic barrier energy for adatom migration on a GaAs (110) surface studied by first-principles calculations

Akira Ishii, Tsuyoshi Aisaka, Ji-Won Oh, Masahiro Yoshita, and Hidefumi Akiyama

Appl. Phys. Lett. 83, 4187 (2003); http://dx.doi.org/10.1063/1.1627945 (3 pages) | Cited 14 times

Online Publication Date: 12 November 2003

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We determined potential-energy surfaces for Ga and As adatoms on a GaAs (110) surface by first-principles calculations in order to understand the epitaxial growth mechanism. We found small migration barrier energies for Ga and As, which explain the long atom-migration length suggested by experiments. We also found that Ga migration is one dimensional and As migration is two dimensional, and that, for both Ga and As adatoms, the sites near As of the topmost layer are stable while those near Ga are unstable. © 2003 American Institute of Physics.
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68.43.Bc Ab initio calculations of adsorbate structure and reactions
68.47.Fg Semiconductor surfaces
68.55.A- Nucleation and growth

Long coherence times at 300 K for nitrogen-vacancy center spins in diamond grown by chemical vapor deposition

T. A. Kennedy, J. S. Colton, J. E. Butler, R. C. Linares, and P. J. Doering

Appl. Phys. Lett. 83, 4190 (2003); http://dx.doi.org/10.1063/1.1626791 (3 pages) | Cited 60 times

Online Publication Date: 12 November 2003

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Electron-spin-echo experiments reveal phase-memory times as long as 58 μs at 300 K for nitrogen-vacancy centers in chemical vapor deposition (CVD) single crystals. The spins were optically polarized and optically detected. Two high-quality CVD samples were studied. From the current results, it is not clear whether these phase-memory times represent a fundamental limit or are limited by an external source of decoherence. © 2003 American Institute of Physics.
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76.30.Lh Other ions and impurities
61.72.Yx Interaction between different crystal defects; gettering effect
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.J- Point defects and defect clusters

Intrinsic compensation of silicon-doped AlGaN

M. C. Wagener, G. R. James, and F. Omnès

Appl. Phys. Lett. 83, 4193 (2003); http://dx.doi.org/10.1063/1.1628396 (3 pages) | Cited 8 times

Online Publication Date: 12 November 2003

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The silicon doping characteristics of AlxGa1−xN were investigated over the x = 0.2–0.5 composition range. A combination of Hall and capacitance–voltage measurements indicated a significant deepening of the Si level, as well as a systematic increase in carrier compensation with increasing compositions. Optical isothermal capacitance transient spectroscopy also revealed the presence of two midgap states with concentrations in the low 1017 cm−3 range. The two levels, which are thought to be responsible for the observed compensation, have been assigned to the third and second ionization states of the aluminum vacancy. © 2003 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
71.55.Eq III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Improved coherent terahertz emission by modification of the dielectric environment

M. Zedler, C. Janke, P. Haring Bolivar, H. Kurz, and H. Künzel

Appl. Phys. Lett. 83, 4196 (2003); http://dx.doi.org/10.1063/1.1628400 (3 pages) | Cited 5 times

Online Publication Date: 12 November 2003

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We present a generally applicable approach to enhance the conversion efficiency from optical input to usable coherent output power for THz emitters based on optically excited charge carriers. Guided by numerical simulations, the dielectric environment of the emitter is modified to improve radiation rate and spatial emission characteristics. The modifications comprise a sapphire layer applied on the semiconductor surface and a gold backside metallization. Comparison between a standard InGaAs semiconductor surface field emitter and an optimized version yields an increase of one order of magnitude in coherently emitted THz power. This result is in close agreement with the numerical simulations. © 2003 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption

High resistivity annealed low-temperature GaAs with 100 fs lifetimes

I. S. Gregory, C. Baker, W. R. Tribe, M. J. Evans, H. E. Beere, E. H. Linfield, A. G. Davies, and M. Missous

Appl. Phys. Lett. 83, 4199 (2003); http://dx.doi.org/10.1063/1.1628389 (3 pages) | Cited 40 times

Online Publication Date: 12 November 2003

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We demonstrate the critical effect of postgrowth annealing temperature on the properties of low-temperature-grown GaAs. By using annealing temperatures substantially below the 500–600 °C commonly reported, GaAs with high resistivity and with carrier lifetimes as short as 100 fs can be routinely obtained. We discuss the optimum, but different, anneal conditions required for terahertz photoconductive emitters and detectors, and illustrate their use in a continuous-wave system. © 2003 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
61.72.Cc Kinetics of defect formation and annealing
84.40.Ba Antennas: theory, components and accessories
85.60.-q Optoelectronic devices
72.40.+w Photoconduction and photovoltaic effects

Strained Si/strained Ge dual-channel heterostructures on relaxed Si0.5Ge0.5 for symmetric mobility p-type and n-type metal-oxide-semiconductor field-effect transistors

Minjoo L. Lee and Eugene A. Fitzgerald

Appl. Phys. Lett. 83, 4202 (2003); http://dx.doi.org/10.1063/1.1627469 (3 pages) | Cited 27 times

Online Publication Date: 12 November 2003

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By growing heterostructures that combine a surface strained Si layer with a buried strained Ge layer on Si0.5Ge0.5, we have fabricated metal-oxide-semiconductor field-effect transistors with mobility enhancement factors over bulk Si of 1.7–1.9 for electrons and 10–12 for holes. While high hole mobility can be attained in strained Si/strained Ge heterostructures grown on Si0.3Ge0.7, we have found the electron mobility in similarly grown heterostructures to be limited by defect scattering in the Si cap. Reducing the Ge content of the virtual substrate to Si0.5Ge0.5 and optimizing the strained Si and strained Ge layer thicknesses allowed the realization of devices where the p-channel mobility as a function of inversion density actually matches or exceeds the n-channel mobility. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Electrical characterization of InGaAs/InP quantum wells by scanning capacitance microscopy

K. Maknys, O. Douhéret, and S. Anand

Appl. Phys. Lett. 83, 4205 (2003); http://dx.doi.org/10.1063/1.1625109 (3 pages) | Cited 15 times

Online Publication Date: 12 November 2003

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In this work, cross-sectional scanning capacitance microscopy (SCM) is used to investigate InGaAs/InP quantum wells. It is demonstrated that SCM is indeed capable of detecting the electrons in the quantum wells and that the SCM signal shows a systematic trend for the different wells. Clear dips in the dC/dV signal are observed at the InGaAs quantum wells and imply carrier densities higher than the surrounding barriers. It is also shown that the depletion regions in the barriers adjacent to the wells can be resolved. The results show that geometric tip-averaging effects significantly influence the imaging of electrons in quantum wells and limit the lateral resolution. © 2003 American Institute of Physics.
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73.63.Hs Quantum wells
68.37.-d Microscopy of surfaces, interfaces, and thin films
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
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