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13 May 1996

Volume 68, Issue 20, pp. 2775-2906

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75 Å GaN channel modulation doped field effect transistors

Jinwook Burm, William J. Schaff, Lester F. Eastman, Hiroshi Amano, and Isamu Akasaki

Appl. Phys. Lett. 68, 2849 (1996); http://dx.doi.org/10.1063/1.116345 (3 pages) | Cited 38 times

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A III–V nitride modulation doped field effect transistor (MODFET) layer structure grown by organometallic vapor phase epitaxy (OMVPE) on a sapphire substrate was employed for transistor fabrication. The MODFET layer structure contained a 75 Å GaN channel, 50 Å Al0.16Ga0.84N spacer, 20 Å Si doped charge supply layer, 130 Å Al0.16Ga0.84N barrier, and 60 Å Al0.06Ga0.94N cap layer. The thin channel (75 Å) was chosen to improve the carrier confinement in the channel. The fabricated MODFET’s had 0.25 μm long gates, and utilized a Au–Si alloy Ohmic metal and a Ti/Pd/Au gate metal. The measured transconductance was 40 mS/mm. From the microwave measurements on devices with 0.25 μm long gates, ft and fmax were determined to be 21.4 and 77.5 GHz, respectively. © 1996 American Institute of Physics.
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85.30.Tv Field effect devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Polarization fields and band offsets in GaInP/GaAs and ordered/disordered GaInP superlattices

Sverre Froyen, Alex Zunger, and A. Mascarenhas

Appl. Phys. Lett. 68, 2852 (1996); http://dx.doi.org/10.1063/1.116346 (3 pages) | Cited 69 times

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Using the first‐principles pseudopotential method we have calculated band offsets between ordered and disordered Ga0.5In0.5P and between ordered GaInP2 and GaAs. We find valence band offsets of 0.10 and 0.27 eV for the two interfaces with the valence band maximum on ordered GaInP2 and GaAs, respectively. Using experimental band gaps these offsets indicate that the ordered/disordered Ga0.5In0.5P interface has type I band alignment and that the ordered GaInP2/GaAs interface has type II alignment. Assuming transitivity of the band offsets, these results suggest a type I alignment between disordered Ga0.5In0.5P and GaAs and a transition from type I to type II as the GaInP side becomes more ordered. Our calculations also show that ordered GaInP2 has a strong macroscopic electric polarization. This polarization will generate electric fields in inhomogeneous samples, strongly affecting the electronic properties of the material. © 1996 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Investigation on direct bonding of III–V semiconductor wafers with lattice mismatch and orientation mismatch

Yae Okuno

Appl. Phys. Lett. 68, 2855 (1996); http://dx.doi.org/10.1063/1.116347 (3 pages) | Cited 11 times

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The direct bonding of various III–V wafers with mismatches in terms of lattice constants and surface orientations was systematically investigated for an In–Ga–As–P system. Many wafer combinations were bonded with sufficient mechanical strength, despite those mismatches. The bonding interface of (001) GaP and (110) InP was observed by transmission electron microscopy and found to be bonded at the atomic level without any defects occurring. The electrical property of the bonding interface was examined for several bonded structures of GaAs and InP. The results support a novel concept ‘‘free‐orientation integration,’’ which should be achieved by direct bonding. © 1996 American Institute of Physics.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Characterization of FeSix film by codeposition on β‐FeSi2 template

Xiangdong Chen, Lianwei Wang, Qinwo Shen, Rushan Ni, and Chenglu Lin

Appl. Phys. Lett. 68, 2858 (1996); http://dx.doi.org/10.1063/1.116348 (3 pages) | Cited 2 times

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We report the characterization of FeSix (x∼3) thin film prepared by simultaneous electron beam evaporation of Fe and Si onto a β‐FeSi2 template at 250 °C. The in situ reflective high energy electron diffraction observation and ex situ cross‐section transmission electron microscope characterization of the as‐deposited film imply that the as‐deposited film has the structure similar to that of β‐FeSi2. But the spreading resistance measurement shows that the film is metallic. Auger electron spectroscopy suggests that the chemical environment of Fe atoms in the as‐deposited FeSix film is different from that in the annealed film (β‐FeSi2 film). We explain this paradox by assuming that the as‐deposited film has the crystal lattice similar to β‐FeSi2 but with ingredient disorder due to the low transport viscosity of Fe and Si atoms at this temperature. © 1996 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.05.J- Electron diffraction and scattering
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Carrier traps in a GaAs/AlxGa1−xAs single electron transistor

T. Sakamoto and K. Nakamura

Appl. Phys. Lett. 68, 2861 (1996); http://dx.doi.org/10.1063/1.116349 (3 pages) | Cited 6 times

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We study carrier traps in a single electron transistor fabricated from a GaAs/AlxGa1−xAs heterostructure. In the heterointerface, there are many kinds of defects, which induce various trap levels in the band gap of AlxGa1−xAs or GaAs. The current through the transistor switches between two states because of trapping and detrapping of a single electron. The gate voltage dependencies of the switching indicate how the traps are spatially distributed. The possibility of the existence of a trap with multilevels is also discussed. © 1996 American Institute of Physics.
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85.35.Gv Single electron devices
72.70.+m Noise processes and phenomena
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Fluorinated amorphous carbon thin films grown by helicon plasma enhanced chemical vapor deposition for low dielectric constant interlayer dielectrics

Kazuhiko Endo and Toru Tatsumi

Appl. Phys. Lett. 68, 2864 (1996); http://dx.doi.org/10.1063/1.116350 (3 pages) | Cited 51 times

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Fluorinated amorphous carbon thin films (a‐C:F) for interlayer dielectrics are grown by helicon plasma enhanced chemical vapor deposition. The source gases are CH4, CF4, C2F 6 and their H2mixtures. a‐C:F films can be fabricated without adding hydrogen using the helicon reactor, while in the previously reported parallel‐plate reactor, no film grows unless a hydrogen source is added. The films grown in the helicon reactor have no hydrogen content. The growth rate of the films reaches 0.3 μm/min (C2F 6) and 0.15 μm/min (CF4). The thickness of the films deposited with C2F6 does not decrease on heating to 300 °C, while the films with CF4 shrink. The dielectric constants of the films deposited from C2F6 and CF4 are 2.4 and 2.3 respectively at 1 MHz. The dielectric loss tangent of these films is 0.01 at 1 MHz. © 1996 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Dominance of tunneling current and band filling in InGaN/AlGaN double heterostructure blue light‐emitting diodes

H. C. Casey, J. Muth, S. Krishnankutty, and J. M. Zavada

Appl. Phys. Lett. 68, 2867 (1996); http://dx.doi.org/10.1063/1.116351 (3 pages) | Cited 87 times

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Measurement of the room temperature forward bias current‐voltage behavior of InGaN/AlGaN double heterostructure blue light‐emitting diodes demonstrates a significant departure from the usual Is exp(qV/ nkT) behavior where n is the ideality factor which varies between 1 and 2. The observed current‐voltage behavior at room temperature may be represented as I=2.7×10−11 exp(5.7V) which suggests a tunneling mechanism. Measurement of the electroluminescence for currents from 0.5 to 100 mA demonstrates that the emission peak shifts to higher energy while increasing in intensity. The shifting peak spectra is due to band filling, a process which results from the injection of holes via tunneling into an empty acceptor impurity band and vacant valence band tails. At currents near 100 mA, a non‐shifting band‐to‐band emission approaches the intensity of the shifting peak spectra. The active layer of these diodes is codoped with both the donor Si and the acceptor Zn. © 1996 American Institute of Physics.
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85.60.Jb Light-emitting devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Gk Tunneling

The influence of TiSi2 and CoSi2 growth on Si native point defects: The role of the diffusing species

S. B. Herner, K. S. Jones, H.‐J. Gossmann, R. T. Tung, J. M. Poate, and H. S. Luftman

Appl. Phys. Lett. 68, 2870 (1996); http://dx.doi.org/10.1063/1.116352 (3 pages) | Cited 8 times

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Boron‐ and Sb‐doped superlattice samples have been used to investigate intrinsic point defects in Si after formation of TiSi2 and CoSi2 films from codeposited metal and Si. The as‐deposited films had the compositions Ti, TiSi0.8, TiSi2.2, and CoSi0.8. After annealing in argon for 1 h at 850 °C, the films formed TiSi2 and CoSi2, respectively. All samples showed the same slight interstitial undersaturation and vacancy supersaturation. Since TiSi2 and all its precursor phases form completely by Si diffusion and the CoSi+Si→CoSi2 transformation occurs by Co diffusion, this indicates that the diffusing species during film growth is not the determining factor in the point defect perturbance in the Si substrate. © 1996 American Institute of Physics.
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61.72.J- Point defects and defect clusters
61.72.uf Ge and Si
66.30.J- Diffusion of impurities

Enhanced hydrogenation in polycrystalline silicon thin films using low‐temperature ultrasound treatment

S. Ostapenko, L. Jastrzebski, J. Lagowski, and R. K. Smeltzer

Appl. Phys. Lett. 68, 2873 (1996); http://dx.doi.org/10.1063/1.116353 (3 pages) | Cited 7 times

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Ultrasound treatment (UST) was applied to improve electronic properties of polycrystalline silicon films on silica‐based substrates. A strong decrease of sheet resistance by a factor of two orders of magnitude was observed in hydrogenated films at UST temperatures lower than 100 °C. This is accompanied by improvement of a film homogeneity as confirmed by spatially resolved photoluminescence study. The UST effect on sheet resistance demonstrates both stable and metastable behavior. A stable UST effect can be accomplished using consecutive cycles of UST and relaxation. An enhanced passivation of grain boundary defects after UST is directly measured by nanoscale contact potential difference with atomic force microscope. Two specific UST processes based on interaction between the ultrasound and atomic hydrogen are suggested: enhanced passivation of grain boundary defects and UST induced metastability of hydrogen related defects. © 1996 American Institute of Physics.
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81.40.Rs Electrical and magnetic properties related to treatment conditions
73.61.Cw Elemental semiconductors

Local barrier heights on quantum wires determined by ballistic electron emission microscopy

C. Eder, J. Smoliner, and G. Strasser

Appl. Phys. Lett. 68, 2876 (1996); http://dx.doi.org/10.1063/1.116354 (3 pages) | Cited 6 times

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In this letter, ballistic electron emission microscopy (BEEM) studies on quantum wire structures are reported. GaAs/AlGaAs heterostructures were laterally patterned with a period of 800 nm by laser holography and wet chemical etching. After evaporation of a 70 Å Au film, wires are directly observed both in sample topography and BEEM current image. The BEEM current is found to be enhanced if the ballistic electrons are injected directly into the wire region. Measurements of local effective barrier heights yield increased values between the wires. In this case, the effective threshold for BEEM current detection is determined by the underlying AlGaAs layer. Thus, the quantum wires are also resolved in a barrier height profile. © 1996 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Gk Tunneling
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Measurement of AlN/GaN (0001) heterojunction band offsets by x‐ray photoemission spectroscopy

J. R. Waldrop and R. W. Grant

Appl. Phys. Lett. 68, 2879 (1996); http://dx.doi.org/10.1063/1.116355 (3 pages) | Cited 96 times

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X‐ray photoemission spectroscopy has been used to measure the valence band offset ΔEv for the AlN/GaN (0001) heterojunction interface. The heterojunction samples were grown by reactive molecular beam epitaxy on 6H–SiC (0001) substrates. A nested interface band alignment with ΔEv=1.36±0.07 eV is obtained (ΔEc/ΔEv=52/48). © 1996 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Determination of the off‐diagonal element of the dielectric tensor without measuring the ellipticity

Chun‐Yeol You and Sung‐Chul Shin

Appl. Phys. Lett. 68, 2882 (1996); http://dx.doi.org/10.1063/1.116319 (3 pages) | Cited 1 time

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In addition to the measurement of the Kerr rotation angle, the measurement of the ellipticity is generally known to be necessary for determining the off‐diagonal element of the dielectric tensor. We have found a new method for determining the off‐diagonal element of the dielectric tensor, without measuring the ellipticity, for a sample deposited on a transparent substrate. © 1996 American Institute of Physics.
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77.22.Ch Permittivity (dielectric function)
78.20.Ls Magneto-optical effects

Magnetostriction characteristics of ultrathin permalloy films

Y. K. Kim and T. J. Silva

Appl. Phys. Lett. 68, 2885 (1996); http://dx.doi.org/10.1063/1.116320 (2 pages) | Cited 29 times

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An abrupt and large increase in the absolute magnitude of λs in sputtered polycrystalline permalloy (Ni81Fe19) films for thicknesses below 7 nm was observed. Permalloy films maintain near‐zero magnetostriction with film thicknesses above 7 nm. Film surface studies and microstructural characterizations suggest that the magnetostriction observed in this study is possibly due to an altered surface morphology of microstructural origin. This observation appears to be critical from the viewpoint of permalloy‐based giant magnetoresistive or spin‐valve sensor fabrication where typical permalloy film thicknesses are 3–10 nm. Because thin films with nonzero magnetostriction can induce an undesirable magnetoelastic anisotropy during sensor operation, the control and adjustment of the film composition seems necessary to minimize magnetostriction. © 1996 American Institute of Physics.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Bb Fe and its alloys
75.47.De Giant magnetoresistance

Oscillatory magnetic interlayer exchange coupling in Fe–N/TiN multilayers

Zhen‐Jun Wang, L. S. Wen, Xiang‐Rong Chang, Y. S. Gu, Zhong‐Zhuo Tian, and J. M. Xiao

Appl. Phys. Lett. 68, 2887 (1996); http://dx.doi.org/10.1063/1.116321 (3 pages) | Cited 3 times

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The discovery of oscillatory interlayer exchange coupling in a new type of ceramic superlattice system Fe–N/TiN, is reported. The magnitude of the exchange coupling was found to oscillate with the thickness of the TiN spacer layer and Fe–N ferromagnetic layer with periods about 0.8 and 0.6 nm, respectively. © 1996 American Institute of Physics.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
81.15.Cd Deposition by sputtering

Molecular‐beam epitaxy of Mn1+xSb thin films and substrate temperature dependence of their magneto‐optical properties

S. Miyanishi, H. Akinaga, and K. Tanaka

Appl. Phys. Lett. 68, 2890 (1996); http://dx.doi.org/10.1063/1.116322 (3 pages) | Cited 17 times

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Ferromagnetic Mn1+xSb thin films have been grown on (001) GaAs substrates by molecular‐beam epitaxy at substrate temperatures (TS) in the range from 50 to 400 °C. The excess Mn composition (x) of the grown films was found to change uniquely depending on TS. The polar magneto‐optical Kerr effect measurement demonstrated a strong TS dependence of Kerr rotation and Kerr ellipticity spectra of Mn1+xSb films from the infrared through ultraviolet wavelength region. A possible origin of the TS dependence of the spectra is discussed in connection with the composition of Mn1+xSb films. © 1996 American Institute of Physics.
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78.20.Ls Magneto-optical effects
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Low‐field microwave magnetoabsorption in manganites

S. D. Tyagi, S. E. Lofland, M. Dominguez, S. M. Bhagat, C. Kwon, M. C. Robson, R. Ramesh, and T. Venkatesan

Appl. Phys. Lett. 68, 2893 (1996); http://dx.doi.org/10.1063/1.116323 (3 pages) | Cited 25 times

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We report the magnetic field dependence of microwave absorption at low fields (200 Oe), in thin film and bulk samples of La1−xBaxMnO3−z. We demonstrate, using a very simple cavity configuration, that the magnetic field sensitivity of the microwave response of the giant magnetoresistance materials offers possibilities of using such materials in devices operating at low fields. Low‐field dc magnetization and ac resistivity measurements are also presented. © 1996 American Institute of Physics.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Dd Nonmetallic ferromagnetic materials
75.47.De Giant magnetoresistance

Lock‐in technique for measuring friction on a nanometer scale

J. Colchero, M. Luna, and A. M. Baró

Appl. Phys. Lett. 68, 2896 (1996); http://dx.doi.org/10.1063/1.116324 (3 pages) | Cited 37 times

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A method for measuring friction forces on a nanometer scale is described. This method combines a lock‐in technique with scanning force and friction microscopy. Essentially, a lock‐in amplifier is used to determine the amplitude of the friction loop, which is measured at high frequency. To demonstrate the capability of this method, the dependence of the friction force with normal load is measured and a two dimensional image is presented. © 1996 American Institute of Physics.
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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
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Millimeter‐wave measurements of phase transitions in thiourea using a gyrotron

G. P. Timms and G. F. Brand

Appl. Phys. Lett. 68, 2899 (1996); http://dx.doi.org/10.1063/1.116325 (3 pages) | Cited 2 times

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In this letter the low temperature phase transitions in a compressed powder sample of thiourea, a ferroelectric, are studied at millimeter wavelengths by the reflection of a beam incident at an angle of 45°. The range of frequencies between 100 and 300 GHz was covered by an Impatt oscillator and a tunable gyrotron. The change in permittivity associated with the ferroelectric transition at 169 K was observed to decrease in magnitude and become less abrupt as the frequency was increased. © 1996 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.22.-d Dielectric properties of solids and liquids

An all‐chromium single electron transistor: A possible new element of single electronics

L. S. Kuzmin, Yu. A. Pashkin, A. N. Tavkhelidze, F.‐J. Ahlers, T. Weimann, D. Quenter, and J. Niemeyer

Appl. Phys. Lett. 68, 2902 (1996); http://dx.doi.org/10.1063/1.116326 (3 pages) | Cited 7 times

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The realization of an all‐chromium single electron tunneling (SET) transistor is reported. Chromium was chosen as a normal metal with small grain structure forming the oxide layer with a low potential barrier and great chemical and thermal stability. The transistor showed classical I‐V curves with an offset voltage of 450 μV and an amplitude of gate modulation of 160 μV. Fitting a tunnel current expression in the experimental I‐V curve gave a height of the potential barrier ϕ=170 meV and a width of the barrier d=16 Å. The SET transistor showed a charge sensitivity of 7×10−4 e/Hz1/2 at 10 Hz. © 1996 American Institute of Physics.
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85.35.Gv Single electron devices
73.23.Hk Coulomb blockade; single-electron tunneling
FREE

Comment on ‘‘Metal‐insulator‐semiconductor inversion layer solar cells by using rapid thermal processing’’ [Appl. Phys. Lett. 67, 697 (1995)]

D. Nagel and R. Sittig

Appl. Phys. Lett. 68, 2905 (1996); http://dx.doi.org/10.1063/1.116327 (1 page)

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Abstract Unavailable
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84.60.Jt Photoelectric conversion
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
FREE

Response to ‘‘Comment on ‘Metal‐insulator‐semiconductor inversion layer solar cells by using rapid thermal processing’ ’’ [Appl. Phys. Lett. 68, 2905 (1996)]

A. Beyer, G. Ebest, and R. Reich

Appl. Phys. Lett. 68, 2906 (1996); http://dx.doi.org/10.1063/1.116328 (1 page)

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Abstract Unavailable
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84.60.Jt Photoelectric conversion
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
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