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21 May 2001

Volume 78, Issue 21, pp. 3163-3363

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Band gap engineering of thin-film electroluminescent devices

Alexey N. Krasnov

Appl. Phys. Lett. 78, 3223 (2001); http://dx.doi.org/10.1063/1.1374236 (3 pages) | Cited 1 time

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We introduce an alternative concept to increase the efficiency and brightness of thin-film electroluminescent (TFEL) devices. The method utilizes band gap engineering of the active layer of the device. The initial steps of our work using a ZnSxSe1−x alloy are also presented to demonstrate the workability of the method. This letter discusses the related obstacles and future potentials of the band gap engineering for monochrome and color TFEL devices. © 2001 American Institute of Physics.
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85.60.Pg Display systems
78.60.Fi Electroluminescence
71.20.Nr Semiconductor compounds
78.66.Hf II-VI semiconductors

Fabrication of GaN suspended microstructures

R. P. Strittmatter, R. A. Beach, and T. C. McGill

Appl. Phys. Lett. 78, 3226 (2001); http://dx.doi.org/10.1063/1.1364504 (3 pages) | Cited 12 times

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We report on a versatile processing technology for the fabrication of micro-electromechanical systems in gallium nitride (GaN). This technology, which is an extension of photo-electrochemical etching, allows for the controlled and rapid undercutting of p-GaN epilayers. The control is achieved through the use of opaque metal masks to prevent etching in designated areas, while the high lateral etch rates are achieved by biasing the sample relative to the solution. For GaN microchannel structures processed in this way, undercutting rates in excess of 30 μm/min have been attained. We propose two mechanisms to account for these high etch rates. © 2001 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning

Field emission from GaN surfaces roughened by hydrogen plasma treatment

Takashi Sugino, Takamitsu Hori, Chiharu Kimura, and Tomohide Yamamoto

Appl. Phys. Lett. 78, 3229 (2001); http://dx.doi.org/10.1063/1.1370979 (3 pages) | Cited 45 times

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GaN layers are grown on sapphire substrates with AlN buffer layers by the metalorganic chemical vapor deposition method. GaN layers are doped with Si. The electron density of the n-type GaN is 2×1017 cm−3. It is found that the GaN surface is etched with hydrogen (H2) plasma produced by supplying microwave power leading to the formation of the roughened surface of GaN. A variation in the surface morphology occurs due to microwave power and gas pressure. Field emission measurements are carried out for GaN with various surface morphologies. It is observed that the turn-on electric field decreases with increasing surface roughness of the GaN. A turn-on electric field of the electron emission is estimated to be as low as 12.4 V/μm. © 2001 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.05.Ea III-V semiconductors
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning

High peak-to-valley ratios observed in InAs/InP resonant tunneling quantum dot stacks

M. Borgstrom, T. Bryllert, T. Sass, B. Gustafson, L.-E. Wernersson, W. Seifert, and L. Samuelson

Appl. Phys. Lett. 78, 3232 (2001); http://dx.doi.org/10.1063/1.1374235 (3 pages) | Cited 22 times

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Resonant tunneling was observed through single InAs quantum dot (QD) stacks embedded in InP barriers with peak-to-valley ratios as high as 85 at 7 K. Negative differential resistance in the current–voltage [I(V)] characteristics was obtained up to a point above the temperature of liquid nitrogen. These features were observed in measurements on low-density QD stacks, in which a macroscopic ohmic contact covered less than 150 QD stacks. Due to the design of the structure, the upper QD in the stack has the function of a zero-dimensional emitter. Electrons easily fill the upper dot, whereas tunneling through the entire structure is only allowed when two states in the dots align energetically, resulting in sharp resonant tunneling peaks with high peak-to-valley ratios. © 2001 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.21.La Quantum dots
73.63.Kv Quantum dots
81.07.Ta Quantum dots

Mechanical deformation of InP and GaAs by spherical indentation

J. E. Bradby, J. S. Williams, J. Wong-Leung, M. V. Swain, and P. Munroe

Appl. Phys. Lett. 78, 3235 (2001); http://dx.doi.org/10.1063/1.1372207 (3 pages) | Cited 46 times

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The mechanical deformation by spherical indentation of both crystalline InP and GaAs was characterized using cross-sectional transmission electron microscopy (XTEM) and atomic force microscopy. All load–unload curves show a discontinuity (or “pop in”) during loading. Slip bands oriented along {111} planes are visible in XTEM micrographs from residual indentations in both materials and no evidence of any phase transformations was found. Higher load indentations (35 mN for InP and 50 mN for GaAs) also revealed subsurface cracking. In contrast no cracking was found beneath a 25 mN InP indent although the hardness and modulus data are almost identical to those of the cracked sample. The subsurface cracks are thought to be nucleated by high stress concentrations caused by dislocation pileup. © 2001 American Institute of Physics.
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62.20.F- Deformation and plasticity
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Percolation transition of thermoelectric properties in PbTe thin films

E. I. Rogacheva, I. M. Krivulkin, O. N. Nashchekina, A. Yu. Sipatov, V. A. Volobuev, and M. S. Dresselhaus

Appl. Phys. Lett. 78, 3238 (2001); http://dx.doi.org/10.1063/1.1357809 (3 pages) | Cited 10 times

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Extrema were observed in the film thickness d dependence of various thermoelectric parameters (Seebeck coefficient S, electrical conductivity σ, Hall coefficient RH, charge carrier mobility μ, and power factor P) of epitaxial PbTe/(001) KCl thin films prepared by thermal evaporation in vacuum and protected from oxidation by an EuS layer. We attribute the observed extrema in properties and the high values of μ and P at d ≈ 50 nm to the percolation transition from an island-like to a continuous film and to the self-organization of the islands, which can occur not only in quantum dot superlattices but also in an individual layer. © 2001 American Institute of Physics.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Lw Thermoelectric effects

Photo-enhanced negative differential resistance and photo-accelerated time-dependent dielectric breakdown in thin nitride-oxide dielectric film

Fen Chen, Baozhen Li, Rajarao Jammy, Roger A. Dufresne, and Alvin W. Strong

Appl. Phys. Lett. 78, 3241 (2001); http://dx.doi.org/10.1063/1.1373409 (3 pages) | Cited 2 times

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Photo-enhanced negative differential resistance (NDR) and photo-accelerated time-dependent dielectric breakdown (TDDB) were observed in thin nitride–oxide (N–O) dielectric film biased with gate negative under tungsten lamp illumination. The photo-induced leakage current and photo-accelerated TDDB show dramatic asymmetry under negative and positive gate bias with constant photo-illumination. Our experiments suggest a unique current conduction mechanism in this nitride thin film. A two-carrier conduction induced positive feedback transport process under negative gate bias, and a two-carrier conduction induced self-limiting transport process under positive gate bias are proposed to qualitatively explain the experimental data. The nitride thin film device possessing a light-enhanced NDR can be employed to develop Si-based optoelectronic devices such as switching and logic control. © 2001 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
73.61.Ng Insulators
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Fq High-field and nonlinear effects
77.22.Jp Dielectric breakdown and space-charge effects

Characteristics of n+–p junction leakage induced by tantalum pentoxide gate insulator and gate reoxidation

Chang-Yong Kang, Young-Gwan Kim, and Dae-Gwan Kang

Appl. Phys. Lett. 78, 3244 (2001); http://dx.doi.org/10.1063/1.1370983 (3 pages) | Cited 1 time

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This letter will present the n+–p junction characteristics in tantalum pentoxide gate dielectric (Ta2O5) and gate reoxidation ambient. The n+–p junctions in n-type metal–oxide–silicon field effect transistor fabricated with different gate dielectrics and post-thermal conditions were characterized by current–voltage measurements. The current–voltage measurements of junction leakage of Ta2O5 gate dielectric without gate reoxidation (MT1) show the hump characteristics due to the precipitates of oxide near the junction depletion regime. And their leakage mechanism is phonon-assisted tunneling, which facilitates the hopping of electrons from the valence band into the shallow attractive Coulomb center via the interface states in the precipitate, leaving holes in the valence band. However, the junction leakage currents of Ta2O5 dielectric with gate reoxidation in hydrogen rich ambient (MT2) are higher than those of thermal oxide samples and their leakage mechanism is Schottky barrier lowering due to the enhanced diffusion of oxygen into the junction depletion region. © 2001 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.05.Cy Elemental semiconductors
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
71.20.Mq Elemental semiconductors
85.30.Tv Field effect devices
73.40.Gk Tunneling
73.20.At Surface states, band structure, electron density of states
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
81.65.Mq Oxidation
72.20.Ee Mobility edges; hopping transport
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Energy level control for self-assembled InAs quantum dots utilizing a thin AlAs layer

J. S. Kim, P. W. Yu, J. Y. Leem, J. I. Lee, S. K. Noh, Jong Su Kim, S. M. Kim, J. S. Son, U. H. Lee, J. S. Yim, and D. Lee

Appl. Phys. Lett. 78, 3247 (2001); http://dx.doi.org/10.1063/1.1373410 (3 pages) | Cited 8 times

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Ground-state energy of InAs quantum dots (QDs) in the GaAs matrix can be changed significantly by introducing a thin AlAs layer (1 nm). The photoluminescence (PL) peak position of the QDs grown directly on the thin AlAs layer is blueshifted by 171 meV from that of the QDs grown without the AlAs layer. QDs grown on an additional GaAs thin layer on top of the AlAs layer have PL peaks systematically redshifted to lower energy as the GaAs layer becomes thicker. Time-resolved PL shows that the QDs have similar lifetimes, attesting to the fact that all the QDs grown in this way are of high quality, although the energy level change is large and a thin AlAs layer is introduced. © 2001 American Institute of Physics.
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73.21.La Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
81.16.Dn Self-assembly
81.07.Ta Quantum dots

Photoreflectance line shape symmetry and quantum-well ground-state exciton energy in vertical-cavity surface-emitting laser structures

Sandip Ghosh, Thomas J. C. Hosea, and Stephanie B. Constant

Appl. Phys. Lett. 78, 3250 (2001); http://dx.doi.org/10.1063/1.1374233 (3 pages) | Cited 16 times

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We report photoreflectance studies on the coupling between the Fabry–Perot cavity mode (CM) and the quantum well (QW) ground-state excitonic feature in vertical-cavity surface-emitting laser structures. Changes in the symmetry of the CM-QW spectral feature occur when the angle of incidence of the probe beam is altered. Using detailed simulations, we explain how this is related to an unusual reversal of the roles of the Seraphin coefficients and QW dielectric function, in determining the line shape. Our study suggests a way to find the exciton energy, in situations where a distinct QW feature is not seen because of large broadening of the QW dielectric function combined with high reflectivity of Bragg mirrors and relatively narrow CM width. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
73.21.Fg Quantum wells
78.67.De Quantum wells
78.30.Fs III-V and II-VI semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Fabrication of wirelike InAs quantum dots on 2°-off GaAs (100) substrates by changing the thickness of the InAs layer

Hyo Jin Kim, Young Ju Park, Young Min Park, Eun Kyu Kim, and Tae Whan Kim

Appl. Phys. Lett. 78, 3253 (2001); http://dx.doi.org/10.1063/1.1362337 (3 pages) | Cited 19 times

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Wirelike InAs quatum dots (QDs) grown on 2°-off (100) GaAs substrates by changing the thickness of the InAs layer were successfully fabricated. The sizes of the InAs QDs along the step lines increased with increasing the thickness of the InAs layer, and their increases were attributed to transform of the InAs QDs into the wirelike InAs QDs. The optimal thicknesses of the InAs layers for the wirelike QDs and the interval of the wirelike QDs were significantly affected by the terrace width resulting from the bunching effect due to the thickness variations of the GaAs buffer layers grown on 2°-off (100) GaAs substrates. These results indicate that these wirelike InAs QDs are useful for applications in nanoelectronic devices, such as wrap gate single electron transistors. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.05.Ea III-V semiconductors
81.07.Ta Quantum dots

Comparative study of current–voltage characteristics of Ni and Ni(Pt)-alloy silicided p+/n diodes

D. Z. Chi, D. Mangelinck, S. K. Lahiri, P. S. Lee, and K. L. Pey

Appl. Phys. Lett. 78, 3256 (2001); http://dx.doi.org/10.1063/1.1374496 (3 pages) | Cited 14 times

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A comparative study of the I–V characteristics of p+/n diodes silicided with a pure Ni and Ni(Pt) alloy has been performed. Higher saturation currents as well as abnormal reverse I–V characteristics were observed for some of the diodes which were silicided with pure Ni at 700 °C while good I–V characteristics were observed for other diodes. Our results show that the forward current in the diodes with good I–V characteristics is dominated by electron diffusion in the p+ region. For diodes with higher saturation currents, it has been concluded that both forward and reverse currents in these diodes are dominated by the current following through Schottky contacts that are formed due to inadvertent penetration of NiSi spikes through the p+ region into n region. The formation of Schottky contact was not observed in diodes silicided with a Ni(Pt) alloy, providing a clear evidence of enhanced thermal stability of Pt containing NiSi. © 2001 American Institute of Physics.
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85.30.Kk Junction diodes
85.40.Ls Metallization, contacts, interconnects; device isolation
85.30.De Semiconductor-device characterization, design, and modeling
73.30.+y Surface double layers, Schottky barriers, and work functions

Photon-induced current of polycrystalline-silicon thin-film transistors

H. Ikeda

Appl. Phys. Lett. 78, 3259 (2001); http://dx.doi.org/10.1063/1.1374224 (3 pages) | Cited 5 times

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Photon-induced current (Iph) in polycrystalline-silicon thin-film transistors (poly-Si TFTs) has been investigated using a line-shaped light beam scanning method. In the off-state region, photon-excited carriers in the channel region diffuse to the drain with the diffusion length independent of the poly-Si grain size. The diffusion length is also independent whether poly-Si is hydrogenated or not. This phenomenon is observed in both n-channel and p-channel TFTs. In the subthreshold region, Iph follows the general transport equation in poly-Si. In the inversion region, Iph is proportional only to the total amount of excited carriers in the channel. © 2001 American Institute of Physics.
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85.30.Tv Field effect devices
73.50.Pz Photoconduction and photovoltaic effects

Tracking of conduction phenomena and degradation in organic light emitting diodes by current noise measurements

M. Sampietro, G. Ferrari, D. Natali, U. Scherf, K. O. Annan, F. P. Wenzl, and G. Leising

Appl. Phys. Lett. 78, 3262 (2001); http://dx.doi.org/10.1063/1.1374516 (3 pages) | Cited 12 times

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Noise current analysis, both in time and frequency, is proposed as a means to sense variations of the microscopic conduction in organic light emitting diodes and to track their time evolution. The sensitivity of the technique would allow to correlate the carriers conduction properties with the corresponding changes in the microscopic morphology of the organic layers as obtained with structural or spectroscopic investigations. The method is shown to be very effective also in sensing the initial state and the growth of organic diodes catastrophic degradation in large advance to current monitoring or other techniques. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.60.Bt Optoelectronic device characterization, design, and modeling
73.61.Ph Polymers; organic compounds
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
73.50.Td Noise processes and phenomena

Lateral current spreading in GaN-based light-emitting diodes utilizing tunnel contact junctions

Seong-Ran Jeon, Young-Ho Song, Ho-Jin Jang, Gye Mo Yang, Soon Won Hwang, and Sung Jin Son

Appl. Phys. Lett. 78, 3265 (2001); http://dx.doi.org/10.1063/1.1374483 (3 pages) | Cited 45 times

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InGaN/GaN multiple-quantum-well light-emitting-diode structures utilizing tunnel contact junctions grown by metalorganic chemical vapor deposition have been demonstrated. The p+/n+ GaN tunnel junctions are located in the upper cladding layers of conventional devices, allowing n-type GaN instead of p-type GaN as a top contact layer. Thus, metal ohmic contacts are done at the same time on the top and the lower contact layers. The reverse-biased tunnel contact junction provides lateral current spreading without semitransparent electrode and spatially uniform luminescence exhibiting an improved radiative efficiency. The tunnel contact junction is shown to be an effective method to make possible hole injection via a lateral electron current, with only a small penalty in voltage drop compared to conventional devices. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.40.Ns Metal-nonmetal contacts
73.40.Gk Tunneling
73.63.Hs Quantum wells
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