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21 Jul 2003

Volume 83, Issue 3, pp. 407-587

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 575 (2003); http://dx.doi.org/10.1063/1.1594830 (3 pages)

P. Yu, M. Mustata, J. J. Turek, P. M. W. French, M. R. Melloch, and D. D. Nolte
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Highly low resistance and transparent Ni/ZnO ohmic contacts to p-type GaN

June O Song, Kyoung-Kook Kim, Seong-Ju Park, and Tae-Yeon Seong

Appl. Phys. Lett. 83, 479 (2003); http://dx.doi.org/10.1063/1.1591236 (3 pages) | Cited 44 times

Online Publication Date: 16 July 2003

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We report on a promising Ni (5 nm)/Al-doped ZnO (AZO) (450 nm) metallization scheme for low resistance and transparent ohmic contacts to p-GaN (5×1017 cm−3). It is shown that the as-deposited Ni/AZO contact shows a nonohmic characteristic due to the insulating nature of the as-deposited AZO. However, annealing the contacts at 450 and 550 °C for 2 min in air ambient results in linear current–voltage characteristics, giving a specific contact resistance of 1.01×10−5 and 8.46×10−6 Ω cm2, respectively. It is further shown that annealing the contact at 550 °C for 5 min produces a specific contact resistance of 6.23×10−6 Ω cm2. The light transmittance of the contacts annealed at 550 °C for 2 min is measured to be higher than 76% at wavelengths in the range of 400–550 nm. It is shown that the Ni/AZO contact could be a suitable scheme for high-performance optical devices. © 2003 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
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.Cc Kinetics of defect formation and annealing
78.40.-q Absorption and reflection spectra: visible and ultraviolet

Conductivity of macromolecular networks measured by electrostatic force microscopy

C. H. Lei, A. Das, M. Elliott, and J. E. Macdonald

Appl. Phys. Lett. 83, 482 (2003); http://dx.doi.org/10.1063/1.1592888 (3 pages) | Cited 24 times

Online Publication Date: 16 July 2003

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High-resolution electrostatic force microscopy (EFM)-phase measurements are reported on molecular networks of semiconductor polymer poly-hexylthiophene (P3HT) and DNA molecules. A lateral resolution of better than 20 nm is demonstrated in EFM-phase images of the P3HT network by detecting the phase shift of the tip along the molecules under electrical bias. Strands of λ-DNA are shown to be highly insulating in comparison to the semiconductor polymer P3HT, with a minimum resistance of ∼ 1×107 Ω cm. © 2003 American Institute of Physics.
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72.80.Tm Composite materials
73.61.Ph Polymers; organic compounds
68.37.Ps Atomic force microscopy (AFM)
73.40.Cg Contact resistance, contact potential
68.35.B- Structure of clean surfaces (and surface reconstruction)

Effects of deep-level defects on ohmic contact and frequency performance of AlGaN/GaN high-electron-mobility transistors

G. H. Jessen, R. C. Fitch, J. K. Gillespie, G. D. Via, B. D. White, S. T. Bradley, D. E. Walker, and L. J. Brillson

Appl. Phys. Lett. 83, 485 (2003); http://dx.doi.org/10.1063/1.1593829 (3 pages) | Cited 6 times

Online Publication Date: 16 July 2003

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We have characterized AlGaN/GaN high-electron-mobility-transistors on sapphire and silicon carbide substrates with electrical and microcathodoluminescence spectral measurements. Quarter wafer-scale comparisons of spectral features in the GaN attributed to donor–acceptor pair (DAP) transitions and yellow luminescence (YL) from deep acceptors show that the specific contact resistance is related to the ratio of the DAP to YL defect emission intensities. This suggests that these defects interact to change the contact resistance locally on the GaN side of the AlGaN/GaN interface. We show that changes in the frequency response of these transistors can be attributed to these defects at the interface. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
71.55.Eq III-V semiconductors
73.40.Cg Contact resistance, contact potential
73.20.Hb Impurity and defect levels; energy states of adsorbed species
78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
73.40.Ns Metal-nonmetal contacts

Tunneling transport in polyoxometalate based composite materials

N. Glezos, P. Argitis, D. Velessiotis, and C. D. Diakoumakos

Appl. Phys. Lett. 83, 488 (2003); http://dx.doi.org/10.1063/1.1594278 (3 pages) | Cited 18 times

Online Publication Date: 16 July 2003

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Molecular materials containing tungsten polyoxometalates as the active elements embedded into polymer matrices are investigated as candidates for electronic device applications. The transport properties of these materials are investigated varying the interelectrode spacing and the polyoxometalate concentration. The I–V characteristics of planar devices reveal a conductivity peak at room temperature conditions for intermolecular distances less than 3 nm and electrode distances less than 100 nm. The transport characteristics are discussed in terms of tunneling mechanisms. © 2003 American Institute of Physics.
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72.80.Tm Composite materials
72.20.Fr Low-field transport and mobility; piezoresistance

Room-temperature electrical conductivity studies of sulfur-modified microcrystalline diamond thin films

S. Gupta, B. R. Weiner, and G. Morell

Appl. Phys. Lett. 83, 491 (2003); http://dx.doi.org/10.1063/1.1591065 (3 pages) | Cited 15 times

Online Publication Date: 16 July 2003

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The room-temperature electrical conductivity of sulfur-incorporated microcrystalline diamond (μc-D:S) thin films synthesized by hot-filament chemical vapor deposition was investigated as a function of sulfur concentration. The films were prepared using a 0.3% CH4/H2 gas mixture and hydrogen sulfide (H2S) as dopant source on intrinsic Si(001) substrates. The μc-D:S films exhibited an increase in n-type conductivity with increase in H2S concentration from 0 to 200 ppm, followed by a decrease in conductivity and sign reversal for the films grown with 500 ppm of H2S. These films were also characterized using scanning electron microscopy, atomic force microscopy, and Raman spectroscopy techniques. The findings are discussed in terms of the role of sulfur in the films. The films grown at the highest [H2S] possess the highest carrier concentration ( ∼ 1.07×1017/cm3) and the lowest carrier Hall mobility (0.01 cm2 V−1 s−1). Since the conductivity is affected by carrier concentration and crystallinity, the relatively low experimental conductivity values are connected to low mobilities arising from crystal defects and grain boundaries induced by sulfur addition, and to low carrier concentrations due to incomplete ionization of S atoms. © 2003 American Institute of Physics.
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73.61.Cw Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.up Other materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Dn Low-field transport and mobility; piezoresistance
81.05.U- Carbon/carbon-based materials
81.05.Cy Elemental semiconductors

Boron pile-up at the interface between plasma enhanced chemical vapor deposited TiSi2 film and BF2-doped Si

Yoon-Jik Lee, Hyun Chul Sohn, and Sung-Woong Chung

Appl. Phys. Lett. 83, 494 (2003); http://dx.doi.org/10.1063/1.1594287 (3 pages) | Cited 1 time

Online Publication Date: 16 July 2003

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We have investigated the redistribution of boron in BF2-doped Si substrate during plasma enhanced chemical vapor deposition (PECVD) of TiSi2 with secondary ion mass spectrometry. Boron concentration was observed to be increased at the TiSi2/Si interface after deposition of PECVD TiSi2. Contact resistance with PECVD TiSi2 was measured to be constant in the range of −30–125 °C, implying that the accumulated boron was electrically active and charge transport was field emission in nature. © 2003 American Institute of Physics.
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61.72.S- Impurities in crystals
73.40.Cg Contact resistance, contact potential
68.35.Ct Interface structure and roughness
81.05.Cy Elemental semiconductors
71.55.Cn Elemental semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

NiAi1.74Al0.26 and NiSi1.83Ga0.17: Two materials with perfect lattice match to Si

Klaus W. Richter and Kurt Hiebl

Appl. Phys. Lett. 83, 497 (2003); http://dx.doi.org/10.1063/1.1594289 (3 pages) | Cited 7 times

Online Publication Date: 16 July 2003

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We report on the preparation and characterization of two materials based on cubic NiSi2 (CaF2-type, cF12, Fmmathm) that show no lattice mismatch to Si and are thus promising materials for perfect epitaxial films grown on silicon. The perfectly lattice-matched materials are special compositions within the extended solid solution phases NiSi2−xAlx and NiSi2−xGax with x = 0.26 for Al and x = 0.17 for Ga, respectively. The variations of bulk lattice parameters with the composition were studied by means of x-ray diffraction and the melting behavior of the solid solution phases was investigated by differential thermal analysis. Both phases are thermally stable up to temperatures around 1000 °C. Phase diagram investigations show that the respective phases are in thermodynamic equilibrium with pure silicon. The electrical conductivity of NiSi2−xAlx and NiSi2−xGax was studied on selected bulk samples between 4.2 and 300 K. Both materials show metallic behavior with specific room-temperature resistivities between 23 and 40 μΩ cm. The difference is mainly due to intrinsic defects in these compounds. © 2003 American Institute of Physics.
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61.66.Dk Alloys
81.10.Fq Growth from melts; zone melting and refining
81.05.Bx Metals, semimetals, and alloys
81.30.Bx Phase diagrams of metals, alloys, and oxides
64.70.D- Solid-liquid transitions
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Direct and inverse photoemission spectroscopy studies of potassium intercalated films of two organic semiconductors

T. Schwieger, M. Knupfer, W. Gao, and A. Kahn

Appl. Phys. Lett. 83, 500 (2003); http://dx.doi.org/10.1063/1.1595151 (3 pages) | Cited 20 times

Online Publication Date: 16 July 2003

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A combined direct and inverse photoemission spectroscopy study of the occupied and unoccupied states of the organic semiconductors ZnPc and α-[N,N′-diphenyl-N,N′-bis(1-naphthyl)-1, 1′-biphenyl-4,4″ diamine] in the pristine and reduced state is presented. The splitting of the lowest unoccupied molecular orbital observed upon potassium intercalation leads to an evaluation of the size of correlation effects in both molecular systems. As expected, the Fermi level is found to shift towards the vacuum level upon intercalation. However, the results clearly demonstrate that the Fermi level in potassium intercalated organic semiconductors cannot a priori be assumed to be pinned at the onset of the lowest unoccupied molecular orbital in all cases. © 2003 American Institute of Physics.
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71.20.Rv Polymers and organic compounds
79.60.Fr Polymers; organic compounds
78.70.-g Interactions of particles and radiation with matter
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.20.Tx Fullerenes and related materials; intercalation compounds

Electrical noise in n- and p-type Ag2Te

L. Jiang and E. R. Nowak

Appl. Phys. Lett. 83, 503 (2003); http://dx.doi.org/10.1063/1.1593820 (3 pages) | Cited 1 time

Online Publication Date: 16 July 2003

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The relatively large and linear magnetoresistance found in nonstoichiometric silver chalcogenides makes them attractive candidates for field sensing applications. We report on the intrinsic electrical noise in bulk, polycrystalline Ag2+δTe. Low-frequency noise is due to resistance fluctuations having a 1/f-like power spectrum. The temperature dependence of the noise magnitude and its spectral slope indicate thermally activated kinetics that we attribute to some form of charge trapping–detrapping process occurring in or near the intergranular regions. The effective magnetic field noise in Ag2+δTe is compared to other materials systems used in field sensing applications. © 2003 American Institute of Physics.
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72.80.Ga Transition-metal compounds
72.70.+m Noise processes and phenomena
72.20.My Galvanomagnetic and other magnetotransport effects
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