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22 Feb 1999

Volume 74, Issue 8, pp. 1057-1183

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Temperature- and field-dependent electron and hole mobilities in polymer light-emitting diodes

L. Bozano, S. A. Carter, J. C. Scott, G. G. Malliaras, and P. J. Brock

Appl. Phys. Lett. 74, 1132 (1999); http://dx.doi.org/10.1063/1.123959 (3 pages) | Cited 186 times

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We have studied the transport properties of electron- and hole-dominated MEH-PPV, poly(2-methoxy,5-(2′-ethyl-hexoxy)-p-phenylene vinylene), devices in the trap-free limit and have derived the temperature-dependent electron and hole mobilities (μ = μ0eγ√E) from the space-charge-limited behavior at high electric fields. Both the zero-field mobility μ0 and electric-field coefficient γ are temperature dependent with an activation energy of the hole and electron mobility of 0.38±0.02 and 0.34±0.02 eV, respectively. At 300 K, we find a zero-field mobility μ0 on the order of 1±0.5×10−7 cm2/V s and an electric-field coefficient γ of 4.8±0.3×10−4 (m/V)1/2 for holes. For electrons, we find a μ0 an order of magnitude below that for holes but a larger γ of 7.8±0.5×10−4 (m/V)1/2. Due to the stronger field dependence of the electron mobility, the electron and hole mobilities are comparable at working voltages in the trap-free limit, applicable to thin films of MEH-PPV. © 1999 American Institute of Physics.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ph Polymers; organic compounds
85.60.Jb Light-emitting devices
73.50.Dn Low-field transport and mobility; piezoresistance

Staggered to straddling band lineups in InAs/Al(As, Sb)

S. Bhargava, H.-R. Blank, E. Hall, M. A. Chin, H. Kroemer, and V. Narayanamurti

Appl. Phys. Lett. 74, 1135 (1999); http://dx.doi.org/10.1063/1.123466 (3 pages) | Cited 9 times

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Ballistic electron emission spectroscopy (BEES) has been used to study both the conduction and valence band offsets between InAs and AlAsSb. With the addition of As to AlSb, the conduction band offset between it and InAs has been found to decrease despite the increase in the band gap. The resulting increase in the valence band causes the InAs/Al(As, Sb) band lineup to change from a staggered (type II) to a straddling (type I). Both room-temperature and low-temperature (77 K) BEES spectra have been taken to determine the band offsets. © 1999 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.20.Nr Semiconductor compounds
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

High efficient biexciton photoluminescence observed from single ZnCdSe quantum wells with continuous wave cold carrier generation

Yanfeng Wei, Daming Huang, Xingjun Wang, Gencai Yu, C. S. Zhu, and Xun Wang

Appl. Phys. Lett. 74, 1138 (1999); http://dx.doi.org/10.1063/1.123467 (3 pages) | Cited 4 times

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Biexciton photoluminescence was observed from single ZnCdSe quantum wells with excitation densities at least three orders of magnitudes lower than those reported in the literature. The very efficient biexciton photoluminescence is essentially due to the cold carrier generation under which the biexciton dissociation by hot carrier collision is greatly suppressed. © 1999 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.-y Excitons and related phenomena

Effect of ion mass on the evolution of extended defects during annealing of MeV ion-implanted p-type Si

S. Fatima, J. Wong-Leung, J. Fitz Gerald, and C. Jagadish

Appl. Phys. Lett. 74, 1141 (1999); http://dx.doi.org/10.1063/1.123468 (3 pages) | Cited 11 times

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Evolution of extended defects during annealing of MeV ion-implanted p-type Si has been characterized using deep level transient spectroscopy and transmission electron microscopy. The p-type Si was implanted with Si, Ge, and Sn ions with varying energies and doses from 5×1012 to 1×1014 cm−2 then annealed at 800 °C for 15 min. For all implanted species, the critical dose for transformation from point to extended defects has been determined. The type of extended defects formed depends upon the mass of the implanted species even though the dose was adjusted to create a similar damage distribution for all implanted species. © 1999 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Analysis of deep levels in a phenylenevinylene polymer by transient capacitance methods

H. L. Gomes, P. Stallinga, H. Rost, A. B. Holmes, M. G. Harrison, and R. H. Friend

Appl. Phys. Lett. 74, 1144 (1999); http://dx.doi.org/10.1063/1.123469 (3 pages) | Cited 30 times

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Transient capacitance methods were applied to the depletion region of an abrupt asymmetric n+−p junction of silicon and unintentionally doped poly[2-methoxy, 5 ethyl (2′ hexyloxy) paraphenylenevinylene] (MEH-PPV). Studies in the temperature range 100–300 K show the presence of a majority-carrier trap at 1.0 eV and two minority traps at 0.7 and 1.3 eV, respectively. There is an indication for more levels for which the activation energy could not be determined. Furthermore, admittance data reveal a bulk activation energy for conduction of 0.12 eV, suggesting the presence of an additional shallow acceptor state. © 1999 American Institute of Physics.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ph Polymers; organic compounds

Interactions between DX centers and hot electrons and holes in Al0.25Ga0.75As/GaAs heterostructure field-effect transistors

D. Dieci, C. Canali, R. Menozzi, M. Pavesi, and A. Cetronio

Appl. Phys. Lett. 74, 1147 (1999); http://dx.doi.org/10.1063/1.123493 (3 pages) | Cited 1 time

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Using power Al0.25Ga0.75As/GaAs heterostructure field-effect transistors (HFETs) and both electrical and electroluminescence measurements, we show here that while at room temperature the electron and hole capture processes at the DX centers present in the AlGaAs are in equilibrium, and therefore no charge buildup leading to drifts in the HFET characteristics may take place, under cryogenic conditions (T<100 K), where the electron and hole capture cross sections of the DX centers are very different, two competing processes of hole and hot electron capture lead to bias-dependent, negative, recoverable HFET threshold voltage shifts. © 1999 American Institute of Physics.
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85.30.Tv Field effect devices
84.40.-x Radiowave and microwave (including millimeter wave) technology
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.55.Eq III-V semiconductors
84.30.Jc Power electronics; power supply circuits
78.60.Fi Electroluminescence
73.50.Fq High-field and nonlinear effects

Growth and thermal stability of pseudomorphic Ge1−yCy/Ge superlattices on Ge(001)

R. Duschl, O. G. Schmidt, W. Winter, K. Eberl, M. W. Dashiell, J. Kolodzey, N. Y. Jin-Phillipp, and F. Phillipp

Appl. Phys. Lett. 74, 1150 (1999); http://dx.doi.org/10.1063/1.123470 (3 pages) | Cited 7 times

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High quality Ge/Ge1−yCy superlattices with nominal carbon contents of 1.2% and 2.1% were grown by molecular beam epitaxy on Ge(001). In transmission electron microscopy the layers are planar and perfectly pseudomorphic without any extended defects observable. The infrared absorption line at 529 cm−1 is attributed to the local vibrational mode of substitutional carbon in germanium. However, in contrast to Si1−yCy alloys where almost 100% of the C is substitutional under optimized growth conditions, x-ray diffraction measurements indicate that the efficiency of carbon incorporation onto substitutional sites is only about 30% for low temperature growth at TS = 200 °C. It reduces further for higher growth temperatures to only about 10% at TS = 300 °C. Post-growth annealing experiments indicate thermal stability up to 450 °C. Annealing at higher temperature results in a reduction of substitutional carbon content. As in the case of Si1−yCy alloys the built-in strain is relaxed by C diffusion and not by nucleation of misfit dislocation. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.66.Li Other semiconductors
78.30.Hv Other nonmetallic inorganics

Spiral growth of InGaN/InGaN quantum wells due to Si doping in the barrier layers

Kenji Uchida, Tao Tang, Shigeo Goto, Tomoyoshi Mishima, Atsuko Niwa, and Jun Gotoh

Appl. Phys. Lett. 74, 1153 (1999); http://dx.doi.org/10.1063/1.123471 (3 pages) | Cited 14 times

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We have examined Si-doping effects in InGaN/InGaN quantum-well (QW) structures, especially the influence of Si-doped InGaN barrier layers on the growth mechanism of QW structures, by atomic force microscopy (AFM) and by photoluminescence (PL) and cathodoluminescence (CL) spectroscopy. Our AFM observations revealed that Si-doped InGaN barriers strongly affect the growth mode of overlying InGaN QW layers. This effect leads to the formation of nanoscale islands (with a density of 108 cm−2) due to spiral growth of the QW layers. The spirally grown nanoscale islands significantly increase the PL intensity. Through spatially resolved CL observations, we found that the number of dot-like CL bright spots increased dramatically when the barrier layers were Si doped, and the increased density of the spots was in good agreement with the increased density of the nanoscale islands observed by AFM. By combining these results, we show that the spirally grown QW structures produced by Si doping of the barriers effectively reduce the fluctuation of the band-gap potential in InGaN QW layers. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.05.Ea III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
61.72.uj III-V and II-VI semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
78.60.Hk Cathodoluminescence, ionoluminescence
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Submicron stacked-junction fabrication from Bi2Sr2CaCu2O8+δ whiskers by focused-ion-beam etching

S.-J. Kim, Yu. I. Latyshev, and T. Yamashita

Appl. Phys. Lett. 74, 1156 (1999); http://dx.doi.org/10.1063/1.123472 (3 pages) | Cited 64 times

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We fabricated submicron-sized intrinsic Josephson junctions by the focused-ion-beam (FIB) etching method. The principal result was a reduction of the in-plane junction area to 0.3 μm2 by direct FIB etching with no degradation in the critical transition temperature (Tc). In the current (I)–voltage (V) characteristics of these stacks, the gap structure and the normal state resistance are clearly observed together with a reduction of the Joule heating and disappearance of the branch structure. The Coulomb staircase structure was found in the I–V curves of submicron junctions as a result of their small effective capacitance of fF order. © 1999 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Jb Electronic structure (photoemission, etc.)
74.50.+r Tunneling phenomena; Josephson effects
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning

Effect of the elastic modulus of the matrix on magnetostrictive strain in composites

Y. Chen, J. E. Snyder, C. R. Schwichtenberg, K. W. Dennis, D. K. Falzgraf, R. W. McCallum, and D. C. Jiles

Appl. Phys. Lett. 74, 1159 (1999); http://dx.doi.org/10.1063/1.123473 (3 pages) | Cited 30 times

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The effect of the matrix material on the magnetostriction of composites containing highly magnetostrictive particles has been studied. Experimental results showed that the elastic modulus of the matrix is an important factor determining the bulk magnetostriction of the composite. For a series of composites with the same volume fraction of magnetostrictive particles but different matrix materials, the bulk magnetostriction was found to increase systematically with decreasing elastic modulus of the matrix. A model theory for the magnetostriction of such composites has been developed, based on two limiting assumptions: uniform strain or uniform stress inside the composite. The theory was then used to predict the magnetostriction of the entire material from the volume fractions of the components, their elastic moduli and magnetostrictions. These predictions were in agreement with the experimental results. It is concluded that to obtain a high magnetostriction and adequate mechanical properties of a composite, the elastic moduli of the magnetostrictive phase and the matrix should be as close as possible in value. © 1999 American Institute of Physics.
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75.80.+q Magnetomechanical effects, magnetostriction
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
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Studies of hydrogen-induced degradation processes in SrBi2Ta2O9 ferroelectric film-based capacitors

J. Im, O. Auciello, A. R. Krauss, D. M. Gruen, R. P. H. Chang, S. H. Kim, and A. I. Kingon

Appl. Phys. Lett. 74, 1162 (1999); http://dx.doi.org/10.1063/1.123474 (3 pages) | Cited 33 times

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It is known that the forming gas (N2–H2 mixture) annealing process required for microcircuit fabrication results in an unacceptable electrical degradation of SrBi2Ta2O9 (SBT) ferroelectric capacitors due mainly to the interaction of H2 with the ferroelectric layer of the capacitor. We have found a strong relationship between changes in the surface composition of the ferroelectric layer and the electrical properties of SBT capacitors as a result of hydrogen annealing. Mass spectroscopy of recoiled ions (MSRI) analysis revealed a strong reduction in the Bi signal as a function of exposure to hydrogen at high temperatures ( ∼ 500 °C). The Bi signal reduction correlates with Bi depletion in the SBT surface region. Subsequent annealing in oxygen at temperatures in the range of 700–800 °C resulted in the recovery of the MSRI Bi signal, corresponding to the replenishment of Bi in the previously Bi-depleted surface region. X-ray diffraction (XRD) analysis (probing the whole SBT film thickness) showed little difference in the XRD spectra of the SBT films before and after hydrogen and oxygen-recovery annealing. The combined results of the MSRI and XRD analyses can be interpreted as an indication that the degradation of the electrical properties of the SBT capacitors, after hydrogen annealing, is mainly due to the degradation of the near surface region of the SBT layer. © 1999 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.35.Dv Composition, segregation; defects and impurities
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

A low-loss composition region identified from a thin-film composition spread of (Ba1−x−ySrxCay)TiO3

H. Chang, I. Takeuchi, and X.-D. Xiang

Appl. Phys. Lett. 74, 1165 (1999); http://dx.doi.org/10.1063/1.123475 (3 pages) | Cited 56 times

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We have generated the thin-film ternary composition spread of (Ba1−x−ySrxCay)TiO3 on an equilateral-triangle-shaped LaAlO3 substrate. Compositional variation within the triangle was achieved by a precisely controlled shutter system inside a pulsed laser deposition chamber, which allows the deposition of precursors with gradient thickness over the length of the substrate. Appropriate postannealing afforded high-quality epitaxial thin films over almost the entire composition region. Mapping of the microwave dielectric properties of the composition-spread chip was performed using a scanning evanescent microwave microscope at 1 GHz. Composition region Ba0.12–0.25Sr0.35–0.47Ca0.32–0.53TiO3 was found to have desirable properties for electronic applications. © 1999 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
84.40.-x Radiowave and microwave (including millimeter wave) technology
77.55.-g Dielectric thin films
68.55.Nq Composition and phase identification
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
81.15.Fg Pulsed laser ablation deposition
61.72.Cc Kinetics of defect formation and annealing

Schottky barrier heights of tantalum oxide, barium strontium titanate, lead titanate, and strontium bismuth tantalate

J. Robertson and C. W. Chen

Appl. Phys. Lett. 74, 1168 (1999); http://dx.doi.org/10.1063/1.123476 (3 pages) | Cited 144 times

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The Schottky barrier heights of various metals on the high permitivity oxides tantalum pentoxide, barium strontium titanate, lead zirconate titanate, and strontium bismuth tantalate have been calculated as a function of the metal work function. It is found that these oxides have a dimensionless Schottky barrier pinning factor S of 0.28–0.4 and not close to 1 because S is controlled by Ti–O-type bonds not Sr–O-type bonds, as assumed in earlier work. The band offsets on silicon are asymmetric with a much smaller offset at the conduction band, so that Ta2O5 and barium strontium titanate are relatively poor barriers to electrons on Si. © 1999 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.At Surface states, band structure, electron density of states
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
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High-quality visible-blind AlGaN p-i-n photodiodes

E. Monroy, M. Hamilton, D. Walker, P. Kung, F. J. Sánchez, and M. Razeghi

Appl. Phys. Lett. 74, 1171 (1999); http://dx.doi.org/10.1063/1.123960 (3 pages) | Cited 66 times

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We report the fabrication and characterization of AlxGa1−xN p-i-n photodiodes (0 ⩽ x ⩽ 0.15) grown on sapphire by low-pressure metalorganic chemical vapor deposition. The devices present a visible rejection of six orders of magnitude with a cutoff wavelength that shifts from 365 to 338 nm. Photocurrent decays are exponential for high load resistances, with a time constant that corresponds to the RC product of the system. For low load resistances, the transient response becomes non-exponential, with a decay time longer than the RC constant. This behavior is justified by the strong frequency dependence of the device capacitance. By an admittance analysis, we conclude that speed is not limited by deep levels, but by substitutional Mg capture and emission time. © 1999 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ey III-V semiconductors

Sub-40 nm PtSi Schottky source/drain metal–oxide–semiconductor field-effect transistors

C. Wang, John P. Snyder, and J. R. Tucker

Appl. Phys. Lett. 74, 1174 (1999); http://dx.doi.org/10.1063/1.123477 (3 pages) | Cited 80 times

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PtSi source/drain p-type metal–oxide–semiconductor field-effect transistors (MOSFETs) have been fabricated at sub-40 nm channel lengths with 19 Å gate oxide. These devices employ gate-induced field emission through the PtSi ∼0.2 eV hole barrier to achieve current drives of ∼350 μA/μm at 1.2 V supply. Delay times estimated by the CV/I metric extend scaling trends of conventional p-MOSFETs to ∼2 ps. Thermal emission limits on/off current ratios to ∼20–50 in undoped devices at 300 K, while ratios of ∼ 107 are measured at 77 K. Off-state leakage can be reduced by implanting a thin layer of fully depleted donors beneath the active region to augment the Schottky barrier height or by use of ultrathin silicon-on-insulator substrates. © 1999 American Institute of Physics.
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85.30.Tv Field effect devices
85.40.Ls Metallization, contacts, interconnects; device isolation
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
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Mechanics of rollable and foldable film-on-foil electronics

Z. Suo, E. Y. Ma, H. Gleskova, and S. Wagner

Appl. Phys. Lett. 74, 1177 (1999); http://dx.doi.org/10.1063/1.123478 (3 pages) | Cited 149 times

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The mechanics of film-on-foil devices is presented in the context of thin-film transistors on steel and plastic foils. Provided the substrates are thin, such transistors function well after the foils are rolled to small radii of curvature. When a substrate with a lower elastic modulus is used, smaller radii of curvature can be achieved. Furthermore, when the transistors are placed in the neutral surface by sandwiching between a substrate and an encapsulation layer, even smaller radii of curvature can be attained. Transistor failure clearly shows when externally forced and thermally induced strains add to, or subtract from, each other. © 1999 American Institute of Physics.
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85.30.Tv Field effect devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Optimal geometry for electron emission from a metallic grating

B. Haddad and L. Schächter

Appl. Phys. Lett. 74, 1180 (1999); http://dx.doi.org/10.1063/1.123479 (3 pages)

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Field emission from a rectangular metallic grating is considered, ignoring space-charge effects. It is shown that there is an optimal geometry of the grooves for extraction of maximum current or current density. © 1999 American Institute of Physics.  
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79.70.+q Field emission, ionization, evaporation, and desorption
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Erratum: “Theoretical performance of midinfrared broken-gap multilayer superlattice lasers” [Appl. Phys. Lett. 70, 3212 (1997)]

Michael E. Flatté and J. T. Olesberg

Appl. Phys. Lett. 74, 1183 (1999); http://dx.doi.org/10.1063/1.123494 (1 page)

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Abstract Unavailable
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42.55.Px Semiconductor lasers; laser diodes
99.10.Cd Errata
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