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27 May 1996

Volume 68, Issue 22, pp. 3063-3198

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Low frequency noise in two‐dimensional metal‐semiconductor field effect transistor

M. E. Levinshtein, S.‐L. Rumyantsev, G. S. Simin, H. Park, W. C. B. Peatman, and M. S. Shur

Appl. Phys. Lett. 68, 3138 (1996); http://dx.doi.org/10.1063/1.115803 (3 pages) | Cited 4 times

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Low frequency noise in the two‐dimensional metal‐semiconductor field effect transistor (2D‐MESFET) is reported. It is shown that the noise level S is rather small. At room temperature the value of Hooge constant α was about 2×10−5 for frequency f=20 Hz. The frequency dependence of the relative spectral density of current fluctuations SI/I2 at 300 K was close to S∼1/f0.6 in the frequency range 20 Hz–20 kHz. Two local maxima were observed in the temperature dependence of S in the ranges 100–180 K and 200–300 K. © 1996 American Institute of Physics.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.70.+m Noise processes and phenomena

Mechanism for the anomalous degradation of Si solar cells induced by high fluence 1 MeV electron irradiation

Masafumi Yamaguchi, Stephen J. Taylor, Sumio Matsuda, and Osamu Kawasaki

Appl. Phys. Lett. 68, 3141 (1996); http://dx.doi.org/10.1063/1.115804 (3 pages) | Cited 30 times

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An anomalous increase in the short‐circuit current Isc of n‐on‐p Si space solar cells, followed by an abrupt decrease in Isc and cell failure has been observed under high fluence (≳1016 cm −2) 1 MeV electron irradiation. A model to explain these phenomena by expressing the change in carrier concentration p, of the base region as a function of the electron fluence is proposed in addition to the well‐known model where Isc decreases by minority‐carrier lifetime reduction under irradiation. The reduction in p due to majority‐carrier trapping by radiation‐induced defects has two effects: broadening of the depletion layer which increases the generated photocurrent, and also an increase in the resistivity of the base layer, resulting in the abrupt decrease of Isc and failure of the solar cells. © 1996 American Institute of Physics.
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84.60.Jt Photoelectric conversion
61.80.Fe Electron and positron radiation effects
72.40.+w Photoconduction and photovoltaic effects
71.55.Cn Elemental semiconductors

Activation energies of Si donors in GaN

W. Götz, N. M. Johnson, C. Chen, H. Liu, C. Kuo, and W. Imler

Appl. Phys. Lett. 68, 3144 (1996); http://dx.doi.org/10.1063/1.115805 (3 pages) | Cited 166 times

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The electronic properties of Si donors in heteroepitaxial layers of GaN were investigated. The n‐type GaN layers were grown by metalorganic chemical vapor deposition and either intentionally doped with Si or unintentionally doped. The samples were evaluated by variable temperature Hall effect measurements and photoluminescence (PL) spectroscopy. For both types of samples the n‐type conductivity was found to be dominated by a donor with an activation energy between 12 and 17 meV. This donor is attributed to Si atoms substituting for Ga in the GaN lattice (SiGa). The range of activation energies is due to different levels of donor concentrations and acceptor compensation in our samples. The assignment of a PL signature to a donor–acceptor pair recombination involving the Si donor level as the initial state of the radiative transition yields the position of the optical Si donor level in the GaN bandgap at ∼Ec–(22±4) meV. A deeper donor level is also present in our GaN material with an activation energy of ∼34 meV which is tentatively assigned to oxygen donors substituting for nitrogen (ON). © 1996 American Institute of Physics.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors

Growth and characterization of bulk InGaN films and quantum wells

S. Keller, B. P. Keller, D. Kapolnek, A. C. Abare, H. Masui, L. A. Coldren, U. K. Mishra, and S. P. Den Baars

Appl. Phys. Lett. 68, 3147 (1996); http://dx.doi.org/10.1063/1.115806 (3 pages) | Cited 61 times

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InGaN bulk layers and single quantum wells were grown by atmospheric pressure metalorganic chemical vapor deposition on c‐plane sapphire. We have found that the incorporation efficiency of indium into InGaN epitaxial layers is strongly dependent on the growth rate of the films. Narrow and bright band edge related luminescence was observed for InGaN films up to an indium content of 20% grown at 700 °C. In0.16Ga0.84N single quantum wells with graded InxGa1−xN barriers showed intense luminescence, with an energy shift towards shorter wavelength with decreasing quantum well thickness. The photoluminescence full width at half‐maximum of the 50 Å thick well was as low as 7.9 nm (59 meV) at 300 K. © 1996 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Cr III-V semiconductors

Highly efficient band‐edge emission from InP quantum dots

Olga I. Mićić, Julian Sprague, Zhenghao Lu, and Arthur J. Nozik

Appl. Phys. Lett. 68, 3150 (1996); http://dx.doi.org/10.1063/1.115807 (3 pages) | Cited 67 times

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High quality InP quantum dots with diameters ranging from 25 to 45 Å, have been prepared; these quantum dots (QDs) show high quantum yields for band‐edge photoluminescence (lowest energy HOMO‐LUMO transition). The wavelength of the blue‐shifted band‐edge emission ranges from about 575 to 730 nm depending on QD size. The quantum yield for photoluminescence is 30% at 300 K and 60% at 10 K; the multiexponential decay of this emission exhibits lifetimes ranging from 5 to 50 ns. Deep red‐shifted emission due to trapping of carriers in defect states on the QD surface which exhibits lifetimes above 500 ns, has been eliminated by treating the QDs with a dilute solution of HF or NH4F. © 1996 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Dielectric function of biaxially strained silicon layer

Hosun Lee and E. D. Jones

Appl. Phys. Lett. 68, 3153 (1996); http://dx.doi.org/10.1063/1.115808 (3 pages) | Cited 8 times

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Dielectric functions of strained silicon layers grown on very thick, relaxed Si1−xGex (x=0.115, 0.3, and 0.37) layers are presented. The effect of tetragonal biaxial strain to the dielectric function is observed to be large near the E1 gap region. We compare the strain‐induced change in the dielectric function of silicon layers with that of SiGe layers and the elasto‐optical (or piezo‐optical) constants of silicon which were measured from bulk Si under uniaxial compressive stress. © 1996 American Institute of Physics.
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73.61.Cw Elemental semiconductors
77.65.-j Piezoelectricity and electromechanical effects

Pulsed supersonic jet epitaxy: A nonthermal approach to silicon growth

Rajeev Malik and Erdogan Gulari

Appl. Phys. Lett. 68, 3156 (1996); http://dx.doi.org/10.1063/1.115809 (3 pages) | Cited 7 times

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In this letter, we demonstrate a unique approach for low temperature epitaxial growth of single crystal silicon films on Si(100). Pulsed supersonic jet epitaxy (PSJE), employs high kinetic energy jets of a disilane‐hydrogen mixture incident on the surface leading to layer by layer growth. Precise control of film thickness and significantly higher sticking coefficients are demonstrated. Growth rate dependence of pulse frequency and its implications are discussed. We have been able to reproducibly deposit good quality single crystalline films at temperatures as low as 400 °C with this technique, without the use of any external activation. © 1996 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Determination of the activation energy ϵ3 for impurity conduction in n‐type 4H–SiC

A. O. Evwaraye, S. R. Smith, W. C. Mitchel, and M. D. Roth

Appl. Phys. Lett. 68, 3159 (1996); http://dx.doi.org/10.1063/1.115810 (3 pages) | Cited 8 times

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Impurity conduction (or hopping conduction) has been observed in the more heavily n‐type 4H–SiC samples by both temperature dependent resistivity measurements and thermal admittance spectroscopy. The measured activation energies ϵ3 for hopping were 4–5 meV and 2.3–3.0 meV, respectively. No evidence of hopping conduction was seen by either method in the sample where ND–NA<1018 cm−3. The thermal admittance spectrum of the lightly n‐type sample showed the two nitrogen levels at 53 and 100 meV.
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71.55.-i Impurity and defect levels
72.20.-i Conductivity phenomena in semiconductors and insulators
72.80.-r Conductivity of specific materials
72.15.-v Electronic conduction in metals and alloys

Size classification of silicon nanocrystals

Renato P. Camata, Harry A. Atwater, Kerry J. Vahala, and Richard C. Flagan

Appl. Phys. Lett. 68, 3162 (1996); http://dx.doi.org/10.1063/1.115811 (3 pages) | Cited 33 times

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We report on the synthesis of size‐classified silicon nanocrystals by differential mobility classification of a polydisperse ultrafine silicon aerosol. Using the described technique, the average nanocrystal size can be tuned by simply adjusting an electric field. Samples of nonagglomerated silicon nanocrystals have been obtained and size control has been achieved within 15%–20% in the 2–10 nm size regime. © 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
81.65.-b Surface treatments

Single‐crystal Si islands on SiO2 obtained via excimer‐laser irradiation of a patterned Si film

H. Jin Song and James S. Im

Appl. Phys. Lett. 68, 3165 (1996); http://dx.doi.org/10.1063/1.115812 (3 pages) | Cited 14 times

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We have developed a single‐pulse based excimer‐laser crystallization technique that transforms photolithographically patterned and SiO2‐encapsulated a‐Si regions into single‐crystal islands on SiO2. The method utilizes the substantial superlateral growth distances that are attainable at high substrate temperatures in combination with precise manipulation of the evolution of the solidification front in order to allow only one of the several grains that originate from the intentionally incompletely melted (i.e., the seed) portion of an island to pass through a constriction and propagate into the rest of the island. This converts the main portion of the island, which extends tens of microns in the lateral dimensions, into a high‐angle‐grain boundary free crystalline material, in so far as the size of the island is commensurate with achievable superlateral growth distances. © 1996 American Institute of Physics.
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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
85.40.Hp Lithography, masks and pattern transfer

Oxidation of GaAs/AlGaAs heterostructures studied by atomic force microscopy in air

F. Reinhardt, B. Dwir, and E. Kapon

Appl. Phys. Lett. 68, 3168 (1996); http://dx.doi.org/10.1063/1.115813 (3 pages) | Cited 18 times

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Oxide growth on cleaved (011) cross sections of GaAs/AlGaAs heterostructures exposed to air was investigated using atomic force microscopy. Measurements of the height profile at constant force provide information on the oxide growth rate as a function of time and Al‐mole fraction. We observe an initial field‐aided oxidation mode that follows the Cabrera–Mott model for metal oxidation. After a critical time, oxidation proceeds more slowly, probably assisted by a thermal diffusion process. We used the dependence of oxide thickness on alloy composition for imaging the Al content in GaAs/AlGaAs heterostructures deposited on nonplanar substrates, with a lateral resolution of ≊1 nm. © 1996 American Institute of Physics.
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81.65.Mq Oxidation
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

A pulse‐driven programmable Josephson voltage standard

S. P. Benz and C. A. Hamilton

Appl. Phys. Lett. 68, 3171 (1996); http://dx.doi.org/10.1063/1.115814 (3 pages) | Cited 94 times

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A voltage standard based on a series array of pulse‐biased, nonhysteretic Josephson junctions is proposed. The output voltage can be rapidly and continuously programmed over a wide range by changing the pulse repetition frequency. Simulations relate the circuit margins to pulse height, width, and frequency. Experimental results on a prototype circuit confirm the expected behavior.
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85.25.Cp Josephson devices
84.30.Sk Pulse and digital circuits
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions

Highly sensitive and wideband optical detection in patterned YBa2Cu3O7−δ thin films

Ken’ichi Tanaka, Yoshiro Arikawa, Matsuo Sekine, Motoichi Ohtsu, Yuichi Harada, and Martin Danerud

Appl. Phys. Lett. 68, 3174 (1996); http://dx.doi.org/10.1063/1.115815 (3 pages) | Cited 1 time

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We have measured the optical responses up to 18 GHz in patterned YBa2Cu3O7−δ thin films at various wavelengths by optical heterodyne mixing. The responsivity of the detectors is higher than 50 V/W below 1 Hz at various wavelengths and the responsivity is 20 mV/W at 780 nm and 150 mV/W at 1.55 μm wavelengths in the regime of the modulation frequency from 3 GHz to 18 GHz. © 1996 American Institute of Physics.
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74.25.N- Response to electromagnetic fields
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors

Processing of highly oriented (Hg1−xRex)Ba2Ca2Cu3O8+δ tape with x∼0.1

R. L. Meng, B. Hickey, Y. Q. Wang, Y. Y. Sun, L. Gao, Y. Y. Xue, and C. W. Chu

Appl. Phys. Lett. 68, 3177 (1996); http://dx.doi.org/10.1063/1.115816 (3 pages) | Cited 15 times

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Highly oriented HgBa2Ca2Cu3O8+δ on Ni tapes with a buffer layer of Cr/Ag have been successfully prepared with a transition temperature of 130 K and a transport critical–current density of 2.5×104 A/cm2 at 77 K in their self‐field. © 1996 American Institute of Physics.
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84.71.Mn Superconducting wires, fibers, and tapes
74.72.-h Cuprate superconductors

Discrete voltage states in one‐dimensional parallel array of Josephson junctions

Y. Braiman, F. Family, and H. G. E. Hentschel

Appl. Phys. Lett. 68, 3180 (1996); http://dx.doi.org/10.1063/1.115817 (3 pages) | Cited 1 time

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We study low‐voltage dynamics in highly discrete one‐dimensional arrays of Josephson junctions. In particular, we focus on the resonant solutions emerging from the locking between the time period of the oscillations of the single junction with the spatial period of the wave propagating across the array. We find that the average voltage across the array scales as V∝(κ−κc)1/2, where κc is the critical value of the coupling. The connections to high voltage solutions are discussed. © 1996 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
05.45.-a Nonlinear dynamics and chaos

Magnetic properties of melt‐textured YBa2Cu3O7 prepared in a solar furnace

S. Reich and T. Godin

Appl. Phys. Lett. 68, 3183 (1996); http://dx.doi.org/10.1063/1.115818 (3 pages) | Cited 1 time

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Magnetic properties of bulk melt‐textured YBa2Cu3O7 prepared in a solar furnace were investigated. The material obtained demonstrates high critical current density of the order of 105 A/cm2 in the field of a 1 T at 50 K. The effective activation energy for flux creep was calculated using Maley’s approach and fits the universal relation: Ueff=U0G(T)(J/Jc)−n, where n=3/2, which agrees with the result predicted by the collective flux creep theory. © 1996 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.25.-q Properties of superconductors

Large exchange bias and its connection to interface structure in FeF2–Fe bilayers

J. Nogués, D. Lederman, T. J. Moran, Ivan K. Schuller, and K. V. Rao

Appl. Phys. Lett. 68, 3186 (1996); http://dx.doi.org/10.1063/1.115819 (3 pages) | Cited 84 times

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Large exchange bias effects (ΔE∼1.1 erg/cm2) were observed in antiferromagnetic (FeF2)–ferromagnetic (Fe) bilayers grown on MgO. The FeF2 grows along the spin‐compensated (110) direction. The FeF2–Fe interface roughness was characterized using specular and diffuse x‐ray diffraction and atomic force microscopy. The magnitude of the exchange bias field HE increases as the interface roughness decreases. These results imply that magnetic domain creation in the antiferromagnet plays an important role. © 1996 American Institute of Physics.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
68.55.-a Thin film structure and morphology

Ferromagnetism above room temperature in Mn–Si–C alloy films

M. Gajdzik, C. Sürgers, M. Kelemen, B. Hillebrands, and H. v. Löhneysen

Appl. Phys. Lett. 68, 3189 (1996); http://dx.doi.org/10.1063/1.115820 (2 pages) | Cited 5 times

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Mn–Si–C alloy films are prepared by e‐beam coevaporation onto a Si substrate held at 600 °C. Ferromagnetism is observed below Tc=(360±5) K with SQUID magnetometry and magneto‐optical Kerr effect. This is the highest Curie temperature Tc yet observed for a Mn‐based alloy. Although the composition determined by Auger depth profiling varies appreciably for different films, their Tc is the same indicating that ferromagnetism is caused by an alloy of well‐defined composition independent of precipitations. © 1996 American Institute of Physics.
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75.50.Cc Other ferromagnetic metals and alloys
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

Magnetic properties and giant magnetoresistance in La0.67Ca0.33MnOx bulk material

X. X. Zhang, R. H. Yu, J. Tejada, G. F. Sun, Y. Xin, and K. W. Wong

Appl. Phys. Lett. 68, 3191 (1996); http://dx.doi.org/10.1063/1.115821 (3 pages) | Cited 12 times

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The magnetic and transport properties of a perovskite‐type crystal sample with a nominal composition La0.67Ca 0.33MnOx have been investigated in the temperature range from 5 to 300 K with applied magnetic fields up to 5 T. Magnetization data obtained in the zero‐field‐cooled process exhibit the magnetic behavior with a Néel temperature, TN∼50 K and Curie temperature, TC∼300 K. The interesting feature in the temperature dependence of magnetoresistance is the appearance of a peak at T∼50 K, with value Δρ/ρ=[ρ(0)−ρ(5 T)]/ρ(5 T)=1300% at the Néel temperature, rather than at Curie temperature. © 1996 American Institute of Physics.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.50.Cc Other ferromagnetic metals and alloys
75.50.Lk Spin glasses and other random magnets

Polymer and polymer/metal interface characterization via Fowler–Nordheim tunneling measurements

I. A. Hümmelgen, L. S. Roman, F. C. Nart, L. O. Péres, and E. L. de Sá

Appl. Phys. Lett. 68, 3194 (1996); http://dx.doi.org/10.1063/1.116056 (3 pages) | Cited 11 times

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In this letter we present a procedure used to characterize metal/polymer interfaces via Fowler‐Nordheim tunneling current measurements and use it to obtain the electron affinity of the PPV (poly p‐phenylene vinylene) and to calculate the metal/PPV barrier heights using different Al/PPV/metal (metal: Ga,In,Sn) structures. © 1996 American Institute of Physics.
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72.80.Le Polymers; organic compounds (including organic semiconductors)
73.40.Gk Tunneling
73.40.Sx Metal-semiconductor-metal structures
FREE

Comment on ‘‘Vertical‐cavity stimulated emission from photopumped InGaN/GaN heterojunctions at room temperature’’ [Appl. Phys. Lett. 65, 520 (1994)]

D. M. Bagnall and K. P. O’Donnell

Appl. Phys. Lett. 68, 3197 (1996); http://dx.doi.org/10.1063/1.116057 (1 page) | Cited 8 times

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Abstract Unavailable
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42.55.Px Semiconductor lasers; laser diodes
78.55.Cr III-V semiconductors
FREE

Response to ‘‘Comment on ‘Vertical‐cavity stimulated emission from photopumped InGaN/GaN heterojunctions at room temperature’ ’’ [Appl. Phys. Lett. 68, 3197 (1996)]

M. Asif Khan, S. Krishnankutty, R. A. Skogman, J. N. Kuznia, D. T. Olson, and T. George

Appl. Phys. Lett. 68, 3198 (1996); http://dx.doi.org/10.1063/1.116058 (1 page)

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Abstract Unavailable
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42.55.Px Semiconductor lasers; laser diodes
78.55.Cr III-V semiconductors
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