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27 Mar 2000

Volume 76, Issue 13, pp. 1641-1784

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A reduced complexity process for organic thin film transistors

Hagen Klauk, David J. Gundlach, Mathias Bonse, Chung-Chen Kuo, and Thomas N. Jackson

Appl. Phys. Lett. 76, 1692 (2000); http://dx.doi.org/10.1063/1.126138 (3 pages) | Cited 43 times

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A simplified device structure for depletion-mode organic thin film transistors is described in which the gate electrode and the source/drain contacts are prepared in the same process step, thus reducing the number of material depositions and photolithography steps. Based on the simplified device structure and using the small-molecule aromatic hydrocarbon pentacene as the active material, organic thin film transistors were fabricated on glass substrates with carrier mobility of 0.6 cm2/V s, on/off current ratio of 105, and subthreshold slope of 0.5 V/decade. © 2000 American Institute of Physics.
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85.65.+h Molecular electronic devices
85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
85.40.Ls Metallization, contacts, interconnects; device isolation

p-type doping with N and Li acceptors of ZnS grown by metalorganic vapor phase epitaxy

L. Svob, C. Thiandoume, A. Lusson, M. Bouanani, Y. Marfaing, and O. Gorochov

Appl. Phys. Lett. 76, 1695 (2000); http://dx.doi.org/10.1063/1.126139 (3 pages) | Cited 18 times

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ZnS layers were grown by metalorganic vapor phase epitaxy on GaAs substrates using diethylzinc, ditertiarybutyl sulphide, and triallylamine as organometallic sources. After postgrowth rapid thermal annealing, the ZnS layers showed p-type conductivity with hole concentrations up to 1018 cm−3. Photoluminescence measurements gave additional indications of the presence of electrically active nitrogen acceptors. In separate experiments, lithium was diffused from a LiH solid source into ZnS layers grown without the nitrogen precursor. High-conductivity p-type material was directly obtained with no need of thermal anneal. © 2000 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
71.55.Gs II-VI semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Ey III-V and II-VI semiconductors
73.61.Ga II-VI semiconductors
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors

Influence of phase fluctuation in external environment on Coulomb blockade in an array system of single tunnel junctions/Ni nanowires

Junji Haruyama, Ken-ichiro Hijioka, Motohiro Tako, and Yuki Sato

Appl. Phys. Lett. 76, 1698 (2000); http://dx.doi.org/10.1063/1.126140 (3 pages) | Cited 2 times

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Correlation of Coulomb blockade (CB) with phase fluctuation caused by mutual Coulomb interaction is reported in an array system of single tunnel junctions directly connected to disordered Ni nanowires. At the voltages lower than CB voltage, temperature dependence of the normalized resistance is classified to the following two regimes by a phase transition temperature (Tc), (1) mutual Coulomb interaction regime (T>Tc) and (2) CB regime (T<Tc). It is found that this Tc is very sensitive to a diffusion coefficient (D) of the mutual Coulomb interaction, resulting in a linear Tc vs D1/2 relation. This relation is interpreted as a result of the competition between the charging energy of the CB and the phase fluctuation energy caused by the multiple Coulomb scattering in the Ni nanowire. It is also reconfirmed by the wire diameter dependence of Tc. © 2000 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling

Hole activation from GaAs:Zn nanoclusters for p-type conduction in ZnSe

I. Suemune, J. Hirose, and A. Ueta

Appl. Phys. Lett. 76, 1701 (2000); http://dx.doi.org/10.1063/1.126141 (3 pages) | Cited 1 time

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Growth of p-type ZnSe has been limited to nitrogen doping in molecular-beam epitaxy. As an alternative to nitrogen doping, GaAs cluster doping is proposed in this letter, where GaAs has small lattice mismatch of 0.28% to ZnSe and can potentially be heavily doped in p type. Hole activation to the valence band of the ZnSe layers could be observed by the reduction of the thickness of the GaAs layers in order to form nanoclusters. This was achieved with alternate supplies of triethylgallium and trisdimethylaminoarsenic, and the net acceptor concentration of ∼ 1017 cm−3 was observed. © 2000 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
73.61.Ga II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.55.Gs II-VI semiconductors
81.05.Dz II-VI semiconductors

Effects of charged self-assembled quantum dots on two-dimensional quantum transport

Qin Wang, N. Carlsson, P. Omling, L. Samuelson, W. Seifert, and H. Q. Xu

Appl. Phys. Lett. 76, 1704 (2000); http://dx.doi.org/10.1063/1.126142 (3 pages) | Cited 7 times

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The influence of a layer of InAs quantum dots on the transport properties of a nearby two-dimensional electron gas (2DEG) in an InGaAs/InP quantum well is investigated. The probability of the scattering between edge states is found to increase as the distance between the layer of the dots and the 2DEG decreases. It is shown that Coulomb scattering by electrons in the charged quantum dots play an important role in the scattering between edge states. An effect of the electrons in the dots is to mediate scattering between spin-split edge states. This is demonstrated by showing that the overshoot effect in the quantum Hall regime is only present when the dots are charged with electrons. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.43.-f Quantum Hall effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
71.70.Di Landau levels

Dislocation scattering in a two-dimensional electron gas

Debdeep Jena, Arthur C. Gossard, and Umesh K. Mishra

Appl. Phys. Lett. 76, 1707 (2000); http://dx.doi.org/10.1063/1.126143 (3 pages) | Cited 72 times

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A theory of scattering by charged dislocation lines in a two-dimensional electron gas (2DEG) is developed. The theory is directed towards understanding transport in AlGaN/GaN high-electron-mobility transistors which have a large number of line dislocations piercing through the 2DEG. The scattering time due to dislocations is derived for a 2DEG in closed form. This work identifies dislocation scattering as a mobility-limiting scattering mechanism in 2DEGs with high dislocation densities. The insensitivity of the 2DEG (as compared to bulk) to dislocation scattering is explained by the theory. © 2000 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Tv Field effect devices
81.05.Ea III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Magnetoresistance in n- and p-type Ag2Te: Mechanisms and applications

H. S. Schnyders, M.-L. Saboungi, and T. F. Rosenbaum

Appl. Phys. Lett. 76, 1710 (2000); http://dx.doi.org/10.1063/1.126144 (3 pages) | Cited 26 times

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We compare the large magnetoresistive response of slightly nonstoichiometric Ag2±δTe for a wide range of hole (p ⩽ 8×1017 cm−3) and electron (n ⩽ 4×1018 cm−3) carrier densities. In the p-type material alone, a characteristic peak in the resistivity ρ(T,H) is dramatically enhanced and moves to higher temperature with increasing magnetic field, resulting in a high field (H ∼ 5 T) magnetoresistance that is sizeable even at room temperature. By contrast, n-type specimens are geared for low-field (H<0.1 T) applications because of a striking linear field dependence of the magnetoresistance that appears to be restricted to the Ag-rich materials. © 2000 American Institute of Physics.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Jc Other crystalline inorganic semiconductors

Effect of nitric oxide annealing on the interface trap densities near the band edges in the 4H polytype of silicon carbide

G. Y. Chung, C. C. Tin, J. R. Williams, K. McDonald, M. Di Ventra, S. T. Pantelides, L. C. Feldman, and R. A. Weller

Appl. Phys. Lett. 76, 1713 (2000); http://dx.doi.org/10.1063/1.126167 (3 pages) | Cited 109 times

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Results of capacitance–voltage measurements are reported for metal–oxide–semiconductor capacitors fabricated using the 4H polytype of silicon carbide doped with either nitrogen (n) or aluminum (p). Annealing in nitric oxide after a standard oxidation/reoxidation process results in a slight increase in the defect state density in the lower portion of the band gap for p-SiC and a significant decrease in the density of states in the upper half of the gap for n-SiC. Theoretical calculations provide an explanation for these results in terms of N passivating C and C clusters at the oxide–semiconductor interface. © 2000 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
81.05.Hd Other semiconductors
61.72.Cc Kinetics of defect formation and annealing
71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states
81.65.Rv Passivation

A study of Ar+ laser-assisted Si doping of GaAs by chemical beam epitaxy

B. Q. Shi and C. W. Tu

Appl. Phys. Lett. 76, 1716 (2000); http://dx.doi.org/10.1063/1.126145 (3 pages)

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Doping results from Ar+ laser-assisted chemical beam epitaxy with triethylgallium, tris(dimethylamino) arsenic, and silicon tetrabromide precursors are reported. Enhancements in the n-type doping concentration are observed with laser irradiation in the substrate–temperature range 390–500 °C. With a 300 W/cm2 irradiation power density, a 70-fold increase in the carrier concentration is obtained at 390 °C substrate temperature. An expression for doping concentration is derived to assess the contribution of laser-induced thermal heating to the observed doping increase. Effects of photogenerated carriers on surface decomposition of metalorganic species are discussed. We postulate that the dramatic increase in carrier concentration at low growth temperatures is due to photolysis of silicon tetrabromide. © 2000 American Institute of Physics.
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81.05.Ea III-V semiconductors
61.72.uj III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.S- Impurities in crystals

Experimental evidence for recombination-assisted leakage in thin oxides

Daniele Ielmini, Alessandro S. Spinelli, and Andrea L. Lacaita

Appl. Phys. Lett. 76, 1719 (2000); http://dx.doi.org/10.1063/1.126146 (3 pages) | Cited 6 times

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Carrier separation experiments in degraded p-channel metal–oxide–semiconductor devices reveal the occurrence of both electron and hole leakage processes. A detailed study of the excess currents as a function of time after stress, stress fluence, and polysilicon doping is presented. Evidence for a linear correlation between electron and hole leakage currents is provided, suggesting that the same defect species are responsible for both leakage phenomena. The dependence on polysilicon gate type confirms this explanation, supporting a leakage model based on trap-assisted tunneling and recombination in oxide traps. © 2000 American Institute of Physics.
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73.61.Ng Insulators
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.25.+i Surface conductivity and carrier phenomena
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Hole-induced transient bandgap renormalization: A mechanism for photo-induced absorption in defect-engineered semiconductors

Paul W. Juodawlkis and Stephen E. Ralph

Appl. Phys. Lett. 76, 1722 (2000); http://dx.doi.org/10.1063/1.126147 (3 pages) | Cited 5 times

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In semiconductors, photoexcitation often results in a transient band edge-absorption bleaching due to the dominance of conduction-band filling over bandgap renormalization. In this letter, we show that the presence of electron traps can act to reverse this behavior so that photoexcitation results in an absorption increase in these same semiconductors. We associate this photo-induced absorption with bandgap renormalization caused by photoexcited holes that remain after the electrons have become trapped. We develop a dynamic model that predicts the wavelength dependence of photo-induced absorption and accurately describes the measured nonlinear-absorption recovery of low-temperature-grown InGaAs/InAlAs multiple quantum wells. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Modification of GaN Schottky barrier interfaces probed by ballistic-electron-emission microscopy and spectroscopy

L. D. Bell, R. P. Smith, B. T. McDermott, E. R. Gertner, R. Pittman, R. L. Pierson, and G. J. Sullivan

Appl. Phys. Lett. 76, 1725 (2000); http://dx.doi.org/10.1063/1.126148 (3 pages) | Cited 6 times

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Ballistic-electron-emission microscopy (BEEM) and spectroscopy have been used to investigate the properties of Au/GaN interfaces. The effects of in situ and ex situ annealing on the starting GaN surface were examined, with the aim of increasing the surprisingly low value of interface electron transmission observed in previous BEEM measurements. BEEM imaging and spectroscopy have demonstrated that much higher, more uniform transmission across the Au/GaN interface can be achieved. However, while methods were identified that increase transmission by more than an order of magnitude, BEEM spectroscopy indicates that annealing can substantially alter the Schottky barrier height. These barrier height changes at moderate temperatures are attributed to vacancy diffusion. © 2000 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
81.05.Ea III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
68.37.Vj Field emission and field-ion microscopy

Effects of alloy disorder on the transport properties of AlxGa1−xN epilayers probed by persistent photoconductivity

K. C. Zeng, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 76, 1728 (2000); http://dx.doi.org/10.1063/1.126149 (3 pages) | Cited 10 times

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The effects of alloy fluctuations on the transport properties of AlxGa1−xN alloys (x ∼ 0.35) have been probed through the use of persistent photoconductivity (PPC). In the PPC state, the electron mobility, μe, as a function of electron concentration, n, in a single sample can be obtained under controlled light illumination conditions. It was found that μe is a constant when n is below a critical value nc and it then increases with n at n>nc. This mobility behavior was attributed to the effects of alloy fluctuations in AlxGa1−xN alloys. As a result, the initial PPC buildup kinetics seen in AlxGa1−xN alloys was quite different from those in better understood semiconductor alloys, such as AlGaAs and ZnCdSe, and is a direct consequence of the observed unique dependence of μe on n. From these measurements, the total density of the tail states below the mobility edge in the conduction band was estimated to be 1.46×1017 cm−3 in a Al0.35Ga0.65N sample. The results were compared with those in II–VI semiconductor alloys and their implications on III-nitride device applications were discussed. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
72.40.+w Photoconduction and photovoltaic effects
73.50.Dn Low-field transport and mobility; piezoresistance

Addition energies and quasiparticle gap of CdSe nanocrystals

Alberto Franceschetti and Alex Zunger

Appl. Phys. Lett. 76, 1731 (2000); http://dx.doi.org/10.1063/1.126150 (3 pages) | Cited 19 times

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Using atomistic pseudopotential wave functions we calculate the quasiparticle gap, the optical gap and the electron and hole addition energies of CdSe nanocrystals. We find that the quasiparticle gap and the addition energies depend strongly on the dielectric constant of the surrounding material, while the optical gap is rather insensitive to the environment. We provide scaling lows for these quantities as a function of the quantum dot size, and compare our results with recent scanning tunneling spectroscopy experiments. © 2000 American Institute of Physics.
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73.22.-f Electronic structure of nanoscale materials and related systems
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Dz II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
61.46.-w Structure of nanoscale materials
71.20.Nr Semiconductor compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
78.66.Hf II-VI semiconductors

Transient and steady-state space-charge-limited currents in polyfluorene copolymer diode structures with ohmic hole injecting contacts

Alasdair J. Campbell, Donal D. C. Bradley, Homer Antoniadis, Mike Inbasekaran, Weishi W. Wu, and Ed P. Woo

Appl. Phys. Lett. 76, 1734 (2000); http://dx.doi.org/10.1063/1.126182 (3 pages) | Cited 47 times

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We report detailed measurements on diode structures containing the electroluminescent polyfluorene copolymer poly(9,9-dioctylfluorene-co-bis-N,N′-(4-methoxyphenyl)-bis-N,N′-phenyl-1,4 phenylenediamine). Ohmic injection of holes is achieved with an oxygen plasma cleaned indium tin oxide (ITO) electrode, untreated ITO coated with a film of poly(ethylenedioxythiophene)/polystyrenesulphonic acid (PEDOT/PSS) and plasma cleaned ITO with PEDOT/PSS. Transient dark injection and time-of-flight mobility measurements and steady state current density versus voltage measurements are then entirely consistent with a positive carrier, trap-free, space-charge-limited current. Injection limited behavior is observed, however, for untreated ITO without PEDOT/PSS and for evaporated Au contacts. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics
72.20.Ht High-field and nonlinear effects
73.50.Fq High-field and nonlinear effects
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning
72.80.Le Polymers; organic compounds (including organic semiconductors)

Effect of silicon doping on the optical and transport properties of InGaN/GaN multiple-quantum-well structures

T. Wang, H. Saeki, J. Bai, T. Shirahama, M. Lachab, S. Sakai, and P. Eliseev

Appl. Phys. Lett. 76, 1737 (2000); http://dx.doi.org/10.1063/1.126151 (3 pages) | Cited 28 times

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Temperature-dependent photoluminescence and transport measurements were performed on the In0.13Ga0.87N:Si/GaN:Si multiple-quantum-well (MQW) structures with different doping levels. By fitting the temperature-dependent emission energy of these samples using the band tail model, an obvious localization effect is observed in lightly doped MQW structures. Correspondingly, the electron mobilities in these structures are significantly higher than those of undoped and heavily doped MQW structures. Furthermore, when the localization effect is stronger, the mobility is higher. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.50.Dn Low-field transport and mobility; piezoresistance
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Surface polarity dependence of Mg doping in GaN grown by molecular-beam epitaxy

L. K. Li, M. J. Jurkovic, W. I. Wang, J. M. Van Hove, and P. P. Chow

Appl. Phys. Lett. 76, 1740 (2000); http://dx.doi.org/10.1063/1.126152 (3 pages) | Cited 51 times

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The effect of surface polarity on the growth of Mg-doped GaN thin films on c-plane sapphire substrates by molecular-beam epitaxy has been investigated. The doping behavior of Mg and resulting conductivity of the doped layers were found to strongly depend on the surface polarity of the growing GaN planes. The samples grown on the Ga-polar face (A face) exhibited a p-type conductivity with a free-hole concentration up to 5×1017 cm−3, while the samples grown on the N-polar face (B face) were highly resistive or semi-insulating. The incorporation of residual impurities (O, Si, and C) in the two different polar surfaces was studied by secondary ion mass spectrometry analysis and its effect on the Mg doping was discussed. Our results suggest that the A face (Ga face) is the favored surface polarity for achieving p-type conductivity during the growth of Mg-doped GaN. © 2000 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Ey III-V semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
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