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4 Sep 2000

Volume 77, Issue 10, pp. 1413-1560

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Photovoltaic and spectral photoresponse characteristics of n-C/p-C solar cell on a p-silicon substrate

K. M. Krishna, M. Umeno, Y. Nukaya, T. Soga, and T. Jimbo

Appl. Phys. Lett. 77, 1472 (2000); http://dx.doi.org/10.1063/1.1290687 (3 pages) | Cited 35 times

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Recent studies have shown the application of amorphous carbon as a semiconductor in C/Si heterojunction photovoltaic solar cells. In this letter, we report the rectifying current–voltage characteristics of the phosphorus-doped carbon/undoped-carbon (n-C/p-C) junction. The p- and n-carbon films were deposited by pyrolysis and ion-beam sputtering, respectively, on a p-Si substrate, using camphor as a natural carbon precursor. The preliminary photovoltaic characteristics of the cell reveals a short-circuit current density of 17.1 mA/cm2, open-circuit voltage of 0.339 V, and photoelectrical conversion efficiency of 1.82%, a reproducible result, under air mass zero and 1 sun illumination conditions. The spectral photoresponse characteristics of the cell of the above configuration was explained in terms of transmission/absorption characteristics of the two individual carbon layers. © 2000 American Institute of Physics.
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84.60.Jt Photoelectric conversion
81.15.Cd Deposition by sputtering
81.05.Cy Elemental semiconductors
73.61.Cw Elemental semiconductors
78.66.Db Elemental semiconductors and insulators

Bilayer quantum transistor

Can-Ming Hu and Detlef Heitmann

Appl. Phys. Lett. 77, 1475 (2000); http://dx.doi.org/10.1063/1.1290695 (3 pages) | Cited 9 times

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The ballistic transport properties of a bilayer structure are studied under the Landau–Büttiker formalism. An oscillatory conductance as a function of the front gate is found. The effect arises from the tunneling, which causes a phase difference between the symmetric and antisymmetric eigenstates. The gate electrode controls the effective tunneling gap and, therefore, the interference. The mechanism may be used to design a bilayer analogue of the spin field-effect transistor without ferromagnetic electrodes. © 2000 American Institute of Physics.
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85.35.Ds Quantum interference devices
73.23.Hk Coulomb blockade; single-electron tunneling

Electrical characterization of TiC ohmic contacts to aluminum ion implanted 4H–silicon carbide

S.-K. Lee, C.-M. Zetterling, E. Danielsson, M. Östling, J.-P. Palmquist, H. Högberg, and U. Jansson

Appl. Phys. Lett. 77, 1478 (2000); http://dx.doi.org/10.1063/1.1290690 (3 pages) | Cited 9 times

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We report on the investigation of epitaxial TiC ohmic contacts to Al ion implanted 4H–SiC. TiC ohmic contacts were formed by coevaporation of Ti and C60 at low temperature (<500 °C). A sacrificial silicon nitride (Si3N4) layer was deposited on the silicon carbide substrate prior to Al implantation in order to reach a high Al dopant concentration at the surface while maintaining a low dose. The combination of epitaxially grown TiC and the silicon nitride layer resulted in a promising scheme to make low resistivity ohmic contacts. The lowest contact resistivity (ρC) and sheet resistance (Rs) of the implanted layer at 25 °C were as low as 2×10−5 Ω cm2 and 0.6 kΩ/□, respectively. © 2000 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
61.72.up Other materials
73.40.Cg Contact resistance, contact potential
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors

Temperature-dependent carrier trapping processes in short period quantum wire superlattices grown by flow rate modulation epitaxy

X. Q. Liu, A. Sasaki, N. Ohno, Xue-Lun Wang, and Mutsuo Ogura

Appl. Phys. Lett. 77, 1481 (2000); http://dx.doi.org/10.1063/1.1290693 (3 pages) | Cited 7 times

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We report the first systematic investigation of the temperature-dependent carrier transferring processes of very short period V-grooved GaAs/AlGaAs quantum wire superlattice structures grown by flow rate-modulated metal-organic vapor phase epitaxy. The one monolayer (1 ML) fluctuation causes carrier confinement in sidewall (111) facet superlattice structures, and is shown to play an important role in the carrier transferring process. At low temperatures, the carrier transfer is blocked by the barriers of 1 ML fluctuation, while at high temperatures the carrier transfer from (111) superlattice to the wire region is shown to be very efficient after thermally overcoming the barriers. The temperature-dependent decay times of the different parts give direct evidence of the carrier transferring process, which demonstrates that the carriers can trap into the wire region within 50 ps at temperatures higher than 100 K. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.55.Cr III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Ea III-V semiconductors

Electronic structures of polycrystalline ZnO thin films probed by electron energy loss spectroscopy

H. C. Ong, J. Y. Dai, K. C. Hung, Y. C. Chan, R. P. H. Chang, and S. T. Ho

Appl. Phys. Lett. 77, 1484 (2000); http://dx.doi.org/10.1063/1.1290596 (3 pages) | Cited 10 times

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The microstructure of polycrystalline ZnO thin films grown on amorphous fused quartz has been studied by transmission electron microscopy and electron energy loss spectroscopy (EELS). The optical functions of the grain and grain boundary of ZnO acquired from EELS are compared to elucidate the mechanism of the formation of self-assemble laser cavities within this material. It is found that the refractive index of the grain boundary is significantly lower than that of the grain due to the lack of excitonic resonance. This large refractive index difference between the grain and grain boundary substantiates the scenario that the formation of laser cavities is caused by the strong optical scattering facilitated in a highly disordered crystalline structure. In addition, our results also imply that the optical characteristics of ZnO have very high tolerance on defects. © 2000 American Institute of Physics.
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71.20.Nr Semiconductor compounds
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
79.20.Kz Other electron-impact emission phenomena
78.66.Hf II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.Mm Grain and twin boundaries
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

High-performance all-polymer integrated circuits

G. H. Gelinck, T. C. T. Geuns, and D. M. de Leeuw

Appl. Phys. Lett. 77, 1487 (2000); http://dx.doi.org/10.1063/1.1290728 (3 pages) | Cited 232 times

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In this letter, we demonstrate the integration of all-polymer field-effect transistors in fully functional integrated circuits with operating frequencies of several kHz. One of the key items is an approach to incorporate low-Ohmic vertical interconnects compatible with an all-polymer approach. Inverters, NAND gates, and ring oscillators with transistor channel lengths down to 1 μm have been constructed. Inverters show voltage amplification at moderate biases and pentacene seven-stage ring oscillators show switching frequencies of a few kHz. The potential to realize large integrated circuits is demonstrated by a 15 bit code generator circuit using several hundreds of devices. The proposed concept was evaluated for three solution-processable organic semiconductors. © 2000 American Institute of Physics.
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85.30.Tv Field effect devices
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
84.30.Sk Pulse and digital circuits
84.30.Ng Oscillators, pulse generators, and function generators
73.61.Ph Polymers; organic compounds

Experimental proof-of-principle investigation of enhanced Z3DT in (001) oriented Si/Ge superlattices

T. Koga, S. B. Cronin, M. S. Dresselhaus, J. L. Liu, and K. L. Wang

Appl. Phys. Lett. 77, 1490 (2000); http://dx.doi.org/10.1063/1.1308271 (3 pages) | Cited 54 times

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An experimental proof-of-principle of an enhanced Z3DT (thermoelectric figure of merit) is demonstrated using (001) oriented Si/Ge superlattices. The highest value of the experimental Z3DT at 300 K for a (001) oriented Si(20 Å)/Ge(20 Å) superlattice is 0.1 using κ = 5 Wm−1 K−1, for the in-plane thermal conductivity, which is a factor of seven enhancement relative to the estimated value of Z3DT = 0.014 for bulk Si. The good agreement between experiment and theory validates our modeling approach (denoted as “carrier pocket engineering”) to design superlattices with enhanced values of Z3DT. Proposals are made to enhance the experimental values of Z3DT for Si/Ge superlattices even further. © 2000 American Institute of Physics.
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73.61.Cw Elemental semiconductors
73.50.Lw Thermoelectric effects
72.20.Pa Thermoelectric and thermomagnetic effects
68.60.Dv Thermal stability; thermal effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Use of multiple electrical pulses to study charge transport in polymer light-emitting diodes

D. J. Pinner, R. H. Friend, and N. Tessler

Appl. Phys. Lett. 77, 1493 (2000); http://dx.doi.org/10.1063/1.1308275 (3 pages) | Cited 4 times

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The method of applying two consecutive voltage pulses is presented as a method to study the dynamics of injected charges in the “off-state,” i.e., after the removal of the applied voltage pulse. Pulses of different widths are used to selectively probe the dynamics of holes and electrons. The use of multiple (>2) pulses is also described as an additional carrier monitoring technique. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices

Lateral epitaxy overgrowth of GaN with NH3 flow rate modulation

X. Zhang, P. D. Dapkus, and D. H. Rich

Appl. Phys. Lett. 77, 1496 (2000); http://dx.doi.org/10.1063/1.1308055 (3 pages) | Cited 16 times

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We demonstrate the effects of NH3 flow modulation on the lateral growth rate and morphology of GaN stripes employing lateral epitaxial overgrowth (LEO) by metalorganic chemical vapor deposition. The self-limiting growth mechanism, enhanced Ga diffusion on the (0001) plane, and Ga lateral supply are used to explain our observations. A lateral overgrowth rate to a vertical growth rate ratio of 2.1 and fully coalesced LEO GaN stripes after 1 h growth have been achieved. © 2000 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.Fx Diffusion; interface formation

Hydrogen passivation of deep levels in n–GaN

A. Hierro, S. A. Ringel, M. Hansen, J. S. Speck, U. K. Mishra, and S. P. DenBaars

Appl. Phys. Lett. 77, 1499 (2000); http://dx.doi.org/10.1063/1.1290042 (3 pages) | Cited 29 times

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Differential postgrowth hydrogen passivation of deep levels in n–GaN grown by metal-organic chemical vapor deposition has been directly observed by means of both deep level transient spectroscopy and deep level optical spectroscopy. Two deep levels found at Ec−Et = 0.62 and 1.35 eV show strong H passivation effects, with their concentrations decreasing by a factor of ⩾30 and ∼14, respectively. The decrease in the 0.62 eV trap concentration together with its correlation with the presence of Mg in n–GaN is consistent with Mg–H complex formation. A band of closely spaced deep levels observed at Ec−Et = 2.64–2.80 eV narrows to Ec−Et = 2.74–2.80 eV after hydrogenation, consistent with hydrogen complexing with VGa3− defects as anticipated by earlier theoretical results. Finally, a deep level at Ec−Et = 3.22 eV likely related to background acceptors remains unaffected by hydrogen. © 2000 American Institute of Physics.
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71.55.Eq III-V semiconductors
81.65.Rv Passivation
81.05.Ea III-V semiconductors
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