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22 Apr 2002

Volume 80, Issue 16, pp. 2821-3018

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Mg and O codoping in p-type GaN and AlxGa1−xN (0<x<0.08)

G. Kipshidze, V. Kuryatkov, B. Borisov, Yu. Kudryavtsev, R. Asomoza, S. Nikishin, and H. Temkin

Appl. Phys. Lett. 80, 2910 (2002); http://dx.doi.org/10.1063/1.1471373 (3 pages) | Cited 16 times

Online Publication Date: 16 April 2002

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We describe Mg and O codoping experiments in gas-source molecular-beam epitaxy of GaN and AlGaN that produce high levels of Mg incorporation and activation. In order to obtain the highest level of Mg incorporation the surface stoichiometry was optimized by adjusting the NH3/Ga and NH3/(Ga+Al) flux ratios. The lowest acceptor activation energy and the highest hole concentration, p = 2×1018 cm−3, were measured in samples of p-GaN and p-AlxGa1−xN with well-defined Mg/O ratios determined by secondary ion mass spectrometry. Measurements of the temperature dependence of diffusion current in p–n junctions formed in Al0.08Ga0.92N and GaN show acceptor activation energy of 195±10 and 145±15 meV, respectively. Low activation energies are attributed to successful codoping. © 2002 American Institute of Physics.
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73.61.Ey III-V semiconductors
61.72.up Other materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.S- Impurities in crystals
68.35.Dv Composition, segregation; defects and impurities

Noncontact potentiometry of polymer field-effect transistors

L. Bürgi, H. Sirringhaus, and R. H. Friend

Appl. Phys. Lett. 80, 2913 (2002); http://dx.doi.org/10.1063/1.1470702 (3 pages) | Cited 160 times

Online Publication Date: 16 April 2002

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We report on high-resolution potentiometry of operating organic thin-film field-effect transistors by means of scanning Kelvin probe force microscopy. It is demonstrated that the measured potential reflects the electrostatic potential of the accumulation layer at the semiconductor/insulator interface. We present data revealing gate bias and lateral electric field dependence of the field-effect mobility in poly(hexylthiophene) at temperatures from 50 to 300 K. © 2002 American Institute of Physics.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
85.30.Tv Field effect devices
07.79.-v Scanning probe microscopes and components
73.61.Ph Polymers; organic compounds
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Dn Low-field transport and mobility; piezoresistance

Strong chemical interaction between indium tin oxide and phthalocyanines

H. Peisert, M. Knupfer, T. Schwieger, and J. Fink

Appl. Phys. Lett. 80, 2916 (2002); http://dx.doi.org/10.1063/1.1471936 (3 pages) | Cited 28 times

Online Publication Date: 16 April 2002

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We present a study of the interface properties between indium tin oxide (ITO) and the well-established molecular organic semiconductor copper phthalocyanine (CuPC) and its fluorinated relative copper tetraflourophthalocyanine (CuPCF4) using photoemission spectroscopy. It is shown that a strong chemical interaction occurs between the PC molecules and ITO which indicates the presence of interface states at these technically relevant interfaces. © 2002 American Institute of Physics.
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79.60.Jv Interfaces; heterostructures; nanostructures
68.35.Fx Diffusion; interface formation
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Pressure-induced resonant Raman scattering in Ge/Si islands

K. L. Teo, L. Qin, Z. X. Shen, and O. G. Schmidt

Appl. Phys. Lett. 80, 2919 (2002); http://dx.doi.org/10.1063/1.1471377 (3 pages) | Cited 8 times

Online Publication Date: 16 April 2002

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Self-assembled Ge islands grown by solid-source molecular-beam epitaxy were investigated by resonant Raman scattering under hydrostatic pressure at room temperature. We utilize the effect of pressure to tune the electronic transition through laser excitation energies in the Ge islands. The pressure coefficient of this resonating electronic transition thus obtained is ∼ 2.7±0.5 meV/kbar, which is significantly smaller than the pressure shift of the El transition in bulk Ge. This is attributed to the fact that the Ge islands are strongly constrained by the surrounding Si lattice, leading to a smaller deformation as compared to the bulk Ge, when subjected to the same pressure. © 2002 American Institute of Physics.
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78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators
62.50.-p High-pressure effects in solids and liquids
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Very high hole mobilities in modulation-doped Ge quantum wells grown by low-energy plasma enhanced chemical vapor deposition

Hans von Känel, Matthias Kummer, Giovanni Isella, Elisabeth Müller, and Thomas Hackbarth

Appl. Phys. Lett. 80, 2922 (2002); http://dx.doi.org/10.1063/1.1470691 (3 pages) | Cited 47 times

Online Publication Date: 16 April 2002

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We report on the fabrication of modulation-doped compressively strained Ge quantum wells by low-energy plasma enhanced chemical vapor deposition. A virtual substrate consisting of a thick linearly graded SiGe buffer layer and a cap layer of constant composition is first grown at a high rate (>5 nm/s). The active layer stack, grown at a reduced rate, contains strain compensating cladding layers with modulation doping above the channel. Mobilities of up to 3000 cm2/V s and 87 000 cm2/V s have been achieved at room temperature and liquid He temperature, respectively. © 2002 American Institute of Physics.
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73.63.Hs Quantum wells
68.65.Fg Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
72.20.Fr Low-field transport and mobility; piezoresistance

Thin-film transistors based on well-ordered thermally evaporated naphthacene films

D. J. Gundlach, J. A. Nichols, L. Zhou, and T. N. Jackson

Appl. Phys. Lett. 80, 2925 (2002); http://dx.doi.org/10.1063/1.1471378 (3 pages) | Cited 92 times

Online Publication Date: 16 April 2002

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We report on organic thin-film transistors fabricated using the small-molecule organic semiconductor naphthacene as the active layer material with device performance suitable for several large-area or low-cost electronics applications. We investigated naphthacene thin films deposited by thermal evaporation onto amorphous substrates held near room temperature. Using atomic-force microscopy and x-ray diffraction we find naphthacene films consist of a high density of submicron-sized grains with a surprisingly high degree of molecular order. Thin-film transistors fabricated using evaporated naphthacene films on thermally oxidized silicon substrates have field-effect mobility larger than 0.1 cm2/V s, current on/off ratio greater than 106, negative threshold voltage, and subthreshold slope of 1 V/decade. © 2002 American Institute of Physics.
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85.30.Tv Field effect devices
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Electrical properties of La-doped strontium titanate thin films

David Olaya, Feng Pan, Charles T. Rogers, and John C. Price

Appl. Phys. Lett. 80, 2928 (2002); http://dx.doi.org/10.1063/1.1470694 (3 pages) | Cited 8 times

Online Publication Date: 16 April 2002

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We report on the properties of lanthanum-doped SrTiO3 thin films grown by off-axis laser ablation on LaAlO3 and SrTiO3 substrates in oxygen partial pressures ranging from 10−8 Torr to 55 mTorr. The La/Sr doping ratio of the ablation target was 1%. The resulting films have carrier densities measured in the range of 4.7–17.5×1019 cm−3 independent of temperature from room temperature to 4 K and low-temperature mobilities as high as 130 cm2/V s. These films are much more tolerant to the presence of oxygen during growth than were similar Nb-doped films reported previously. © 2002 American Institute of Physics.
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73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.15.Fg Pulsed laser ablation deposition
74.50.+r Tunneling phenomena; Josephson effects
72.20.My Galvanomagnetic and other magnetotransport effects
68.55.-a Thin film structure and morphology
72.20.Fr Low-field transport and mobility; piezoresistance

Gallium distribution in the clathrates Sr8Ga16Ge30 and Sr4Eu4Ga16Ge30 by resonant diffraction

Yuegang Zhang, Peter L. Lee, George. S. Nolas, and Angus P. Wilkinson

Appl. Phys. Lett. 80, 2931 (2002); http://dx.doi.org/10.1063/1.1473236 (3 pages) | Cited 28 times

Online Publication Date: 16 April 2002

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The distribution of gallium/germanium in the type-I clathrates Sr8Ga16Ge30 and Sr4Eu4Ga16Ge30 over the three crystallographically distinct framework sites has been determined by resonant diffraction. The analyses indicate a strong preference for the occupation of the 6c site by gallium. This is consistent with theoretical predictions, but contrary to the results of a previous neutron diffraction study. The gallium distribution, and, hence, the thermoelectric properties of these materials, may be amenable to manipulation by heat treatment. © 2002 American Institute of Physics.
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61.66.Fn Inorganic compounds
72.20.Pa Thermoelectric and thermomagnetic effects

Effect of Pd or Pt addition to Ti/Al ohmic contact materials for n-type AlGaN

S. Murai, H. Masuda, Y. Koide, and Masanori Murakami

Appl. Phys. Lett. 80, 2934 (2002); http://dx.doi.org/10.1063/1.1471931 (3 pages) | Cited 22 times

Online Publication Date: 16 April 2002

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Effects of Pd or Pt addition to Ti/Al ohmic contact materials used for n-type Al0.2Ga0.8N grown on the GaN substrates were studied where Si with 2×1018 cm−3 were doped in the AlGaN layers. The contact metals were prepared by depositing either by the electron-beam or thermal evaporation technique, and then annealed at high temperatures for 30 s in N2 atmosphere. It was found that the addition of a small amount of Pd or Pt to the Ti/Al ohmic contact materials reduced the contact resistivities of the Ti/Al contacts. The lowest contact resistivity of 4.1×10−6 Ω cm2 was obtained in the Ti(20 nm)/Pd(5 nm)/Al(200 nm) contact after annealing at 600 °C (where a slash “/” indicates the deposition sequence). The reduction of the contact resistivities by the Pd or Pt addition was believed to be due to increase in the donor concentration in the AlGaN layers by forming Pd–Ga or Pt–Ga compounds in the contact metals after annealing at elevated temperatures. © 2002 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
61.72.Cc Kinetics of defect formation and annealing
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Low-resistant and high-transparent Ru/Ni ohmic contact on p-type GaN

Ho Won Jang, W. Urbanek, M. C. Yoo, and Jong-Lam Lee

Appl. Phys. Lett. 80, 2937 (2002); http://dx.doi.org/10.1063/1.1474609 (3 pages) | Cited 22 times

Online Publication Date: 16 April 2002

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We report a low-resistant and high-transparent Ru-based ohmic contact on p-type GaN through oxidation annealing under O2 atmosphere. A low resistivity of 4.5×10−5 Ω cm2 and high light transmittance (84.6%) were simultaneously obtained from oxidized Ru (50 Å)/Ni (50 Å) contact. The RuO2 formed on p-type GaN played a role in reducing the effective Schottky barrier height for injection of holes and NiO layer produced on the RuO2 acted as a diffusion barrier for the outdiffusion of released Ga and N atoms, resulting in the reduction of the contact resistivity as well as the enhancement of light transmission. © 2002 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
81.40.Tv Optical and dielectric properties related to treatment conditions
81.40.Rs Electrical and magnetic properties related to treatment conditions
78.66.Fd III-V semiconductors
81.65.Mq Oxidation
81.40.Gh Other heat and thermomechanical treatments
73.30.+y Surface double layers, Schottky barriers, and work functions
68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers

Probing the SiGe virtual substrate by high-resolution channeling contrast microscopy

H. L. Seng, T. Osipowicz, T. C. Sum, E. S. Tok, G. Breton, N. J. Woods, and J. Zhang

Appl. Phys. Lett. 80, 2940 (2002); http://dx.doi.org/10.1063/1.1474597 (3 pages) | Cited 4 times

Online Publication Date: 16 April 2002

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Relaxed, epitaxial SiGe layers with low densities of threading dislocations are grown by linearly grading the Ge composition. However, such compositionally graded SiGe layers (virtual substrates) often result in a cross hatch surface morphology which affects subsequent device processing. Here, we report on high-resolution channeling-contrast-microscopy (CCM) measurements on such virtual substrates grown by gas-source molecular-beam epitaxy and low-pressure chemical vapor deposition. A two-MeV He+ beam focused to a submicron spot is used in these CCM measurements to obtain both lateral and depth-resolved information on the cross hatch features observed and their association with a slight lattice tilt. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
61.80.Jh Ion radiation effects
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.82.Fk Semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
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