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16 May 1994

Volume 64, Issue 20, pp. 2619-2748

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Analytical closed form expressions for the effective band edges in shallow quantum wells

Jasprit Singh

Appl. Phys. Lett. 64, 2694 (1994); http://dx.doi.org/10.1063/1.111494 (3 pages) | Cited 5 times

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Shallow quantum wells are widely used in electronic and optoelectronic heterostructure devices. However, to determine the effective band edges, one needs numerical techniques unless the barrier height is infinite. In this letter the nearly free electron approach used in periodic structures is exploited to provide accurate energy level expressions for the electronic ground state in a number of important quantum wells with different shapes. These include the square quantum well without and with an applied transverse electric field.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Growth of single crystal Ge films on GaAs and InGaP and highly oriented Au films on Ge

M. Dubey, K. A. Jones, D. W. Eckart, L. M. Casas, and R. L. Pfeffer

Appl. Phys. Lett. 64, 2697 (1994); http://dx.doi.org/10.1063/1.111495 (3 pages) | Cited 4 times

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Single crystal germanium films were deposited on (100) GaAs and InGaP substrates, and highly oriented gold films were deposited on the germanium films by ultrahigh vacuum E‐beam evaporation. They were characterized by double crystal x‐ray diffraction (DXRD), transmission electron microscopy (TEM), Rutherford backscattering spectroscopy (RBS), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM). The germanium film grew epitaxially with a smooth, abrupt interface, and the highly oriented gold film formed a smooth interface with the germanium and had a (100)Au∥(100)Ge and (001)Au∥[011]Ge or [001]Au∥[0‐1 1]Ge orientation relationship. Large grains with one or the other orientation relationship could be distinguished in the SEM. TEM micrographs show that the grains have a periodic dislocation pattern indicative of heteroepitaxy, and the grain boundaries appear to have a low energy. No contamination was detected in the gold film away from the interface with the germanium, and there was significant channeling of the RBS beam when it was normal to the gold film.
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68.55.-a Thin film structure and morphology
85.40.Ls Metallization, contacts, interconnects; device isolation

Improved efficiency of crystalline silicon solar cells due to He+ implantation

J. Bruns, W. Seifert, P. Wawer, H. Winnicke, D. Bräunig, and H. G. Wagemann

Appl. Phys. Lett. 64, 2700 (1994); http://dx.doi.org/10.1063/1.111496 (3 pages) | Cited 3 times

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The influence of He+ implantation on the properties of crystalline silicon solar cells has been investigated. The implantation of 550 keV He+ ions into the masked surface of solar cells was used to form a two‐dimensional defect layer inside the cell space‐charge region. For suitable implantation doses it is possible to increase the photocurrent without degenerating the values for open circuit voltage thus resulting in an improved efficiency of the cells.
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84.60.Jt Photoelectric conversion
72.40.+w Photoconduction and photovoltaic effects
61.80.Jh Ion radiation effects

Electrochemical capacitance‐voltage analysis of delta‐doped pseudomorphic high electron mobility transistor material

C. E. Stutz, B. Jogai, D. C. Look, J. M. Ballingall, and T. J. Rogers

Appl. Phys. Lett. 64, 2703 (1994); http://dx.doi.org/10.1063/1.111471 (3 pages) | Cited 12 times

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This work shows how electrochemical capacitance‐voltage (EC‐V) measurements can be used to evaluate delta‐doped pseudomorphic high electron mobility transistor material. These EC‐V measurements are compared with magnetic‐field‐dependent Hall effect (M‐Hall) measurements and a self‐consistent Poisson/k⋅p calculation of the band structure and electron concentration. The EC‐V technique can clearly delineate the cap layer, the delta‐doped layer, and the InxGa1−xAs channel layer, whereas the M‐Hall method characterizes only the cap and InxGa1−xAs channel layers. The amount of electron charge seen by the EC‐V and M‐Hall measurements show good agreement with theory.
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85.30.De Semiconductor-device characterization, design, and modeling
73.40.Mr Semiconductor-electrolyte contacts
73.61.Ey III-V semiconductors

GaAs metal insulator semiconductor capacitors and high transconductance metal insulator semiconductor field effect transistors

J. Reed, Z. Fan, G. B. Gao, A. Botchkarev, and H. Morkoç

Appl. Phys. Lett. 64, 2706 (1994); http://dx.doi.org/10.1063/1.111472 (3 pages) | Cited 19 times

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We have fabricated 3 μm gate length self‐aligned, depletion mode GaAs metal insulator semiconductor field effect transistors exhibiting transconductances, typically in the vicinity of 160 mS/mm. This achievement is attributed to the use of Si3N4 as the gate dielectric with a few monolayers of a Si/Ge interface layer between the GaAs channel layer and the insulator. The Si3N4/Si/Ge insulator structure is grown in situ using a plasma‐enhanced chemical vapor deposition system which is connected by an ultrahigh vacuum transfer tube to an adjacent III‐V molecular beam epitaxy system. Nearly ideal capacitance‐voltage curves (compared to previous publications) suggest the existence of a high quality insulator/semiconductor interface. The lowest interface trap density that has been measured, as determined from the magnitude of the conductance peak is ∼2×1011 eV−1 cm−2.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Influence of deposition pressure on the bulk and interface states in low pressure chemical vapor deposited polycrystalline silicon thin‐film transistors

C. A. Dimitriadis, D. H. Tassis, N. A. Economou, and G. Giakoumakis

Appl. Phys. Lett. 64, 2709 (1994); http://dx.doi.org/10.1063/1.111473 (3 pages) | Cited 2 times

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The effect of deposition pressure, p, on the bulk and interface states of undoped low pressure chemical vapor deposited polycrystalline silicon thin‐film transistors (polysilicon TFTs) is investigated by field‐effect conductance activation energy measurements. The bulk states consist of deep states with a characteristic wide peak near the midgap and shallow exponential tails near the conduction band. The interface states show an exponential distribution which cause a faster change of the gap states density near the conduction‐band edge. For p≳40 mTorr, the bulk and interface states are controlled by the grain size and the degree of disorder of the material. For p<40 mTorr, the experimental results indicate that the films are contaminated by some impurities. The concentration of these impurities increases as p decreases and contributes mainly to the deep states generation.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Heteroepitaxial growth of tin‐doped indium oxide films on single crystalline yttria stabilized zirconia substrates

Masayuki Kamei, Teruyuki Yagami, Satoru Takaki, and Yuzo Shigesato

Appl. Phys. Lett. 64, 2712 (1994); http://dx.doi.org/10.1063/1.111474 (3 pages) | Cited 28 times

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Heteroepitaxial growth of tin‐doped indium oxide (ITO) film was achieved for the first time by using single crystalline yttria stabilized zirconia (YSZ) as substrates. The epitaxial relationship between ITO film and YSZ substrate was ITO[100]∥YSZ[100]. By comparing the electrical properties of this epitaxial ITO film with that of a randomly oriented polycrystalline ITO film grown on a glass substrate, neither the large angle grain boundaries nor the crystalline orientation were revealed to be dominant in determining the carrier mobility in ITO films.
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68.55.-a Thin film structure and morphology
73.61.Le Other inorganic semiconductors

Dielectric properties of electron‐beam deposited Ga2O3 films

M. Passlack, N. E. J. Hunt, E. F. Schubert, G. J. Zydzik, M. Hong, J. P. Mannaerts, R. L. Opila, and R. J. Fischer

Appl. Phys. Lett. 64, 2715 (1994); http://dx.doi.org/10.1063/1.111452 (3 pages) | Cited 38 times

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We have fabricated high quality, dielectric Ga2O3 thin films. The films with thicknesses between 40 and 4000 Å were deposited by electron‐beam evaporation using a single‐crystal high purity Gd3Ga5O12 source. Metal‐insulator‐semiconductor (MIS) and metal‐insulator‐metal structures (MIM) were fabricated in order to determine dielectric properties, which were found to depend strongly on deposition conditions such as substrate temperature and oxygen pressure. We obtained excellent dielectric properties for films deposited at substrate temperatures of 40 °C with no excess oxygen and at 125 °C with an oxygen partial pressure of 2×10−4 Torr. Specific resistivities ρ and dc breakdown fields Em of up to 6×1013 Ω cm and 2.1 MV/cm, respectively, were measured. Static dielectric constants between 9.93 and 10.2 were determined for these films. Like in other dielectrics, the current transport mechanisms are found to be bulk rather than electrode controlled.
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77.55.-g Dielectric thin films
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
77.22.-d Dielectric properties of solids and liquids
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Metal ion dependent luminescence effects in metal tris‐quinolate organic heterojunction light emitting devices

P. E. Burrows, L. S. Sapochak, D. M. McCarty, S. R. Forrest, and M. E. Thompson

Appl. Phys. Lett. 64, 2718 (1994); http://dx.doi.org/10.1063/1.111453 (3 pages) | Cited 66 times

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We present a systematic analysis of the relationship between the photoluminescence (PL), light emitting device electroluminescence (EL), and conducting properties of a series of metalquinolates, Mq3, where M is a metal (Al, Ga, In, or Sc), and q3 is tris‐(8‐hydroxyquinoline). We compare the solution and thin film PL quantum yields and spectra of each quinolate with the EL quantum efficiencies of organic heterojunction light emitting diodes using the compound as the emitter layer. Our results indicate that, contrary to previous reports, the relative PL yield is not a good indicator of the EL quantum efficiency of a particular material. Specifically, we find that while the PL of Alq3 films is four times that of Gaq3, light emitting devices made from these two materials have comparable electroluminescence quantum efficiencies and long‐term stabilities. Furthermore, the Gaq3 devices have an approximately 50% higher power efficiency than Alq3 structures, suggesting that Gaq3 is a superior emitter material for display applications.
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78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
85.60.Jb Light-emitting devices

Capture and recombination of acceptor bound excitons in the transition region from a two‐dimensional to a quasi‐three‐dimensional GaAs/AlGaAs system

Q. X. Zhao, P. O. Holtz, C. I. Harris, B. Monemar, and E. Veje

Appl. Phys. Lett. 64, 2721 (1994); http://dx.doi.org/10.1063/1.111454 (3 pages) | Cited 3 times

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The capture and recombination processes for acceptor bound excitons (BEs) have been studied for GaAs/AlGaAs multiple quantum well structures, by varying the barrier thickness for a constant 100 Å well width. The observed decay time for the acceptor BE increases rapidly with decreasing barrier width, and is determined by the relative confinement of the electron and hole wave functions. The capture rate of free excitons to the BE state of the neutral acceptor increases by about a factor 7 from a two‐dimensional to a three‐dimensionlike system.  
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78.55.Cr III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.47.-p Spectroscopy of solid state dynamics
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Hydrogenation of GaN, AlN, and InN

J. M. Zavada, R. G. Wilson, C. R. Abernathy, and S. J. Pearton

Appl. Phys. Lett. 64, 2724 (1994); http://dx.doi.org/10.1063/1.111455 (3 pages) | Cited 42 times

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Hydrogen incorporation depths of ≥1 μm are measured for 2H plasma exposure of GaN and AlN at 250–400 °C for 30 min. The concentration of 2H incorporated is in the range 5–10×1017 cm−3 for GaN and 5–30×1018 cm−3 for AlN under these conditions. No redistribution of the hydrogen is observed for annealing temperatures up to 800 °C, but at 900 °C there is substantial loss of hydrogen from the samples. Similar results are obtained for 2H implantation into GaN, AlN, and InN, with no significant redistribution observed up to 500–600 °C in either AlN or InN, and motion only at 900 °C in GaN. The thermal stability of hydrogen in III‐V nitrides explains previous results for Mg‐doped GaN grown using NH3, where post‐growth annealing at high temperatures was required to achieve appreciable doping efficiencies.
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61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
66.30.J- Diffusion of impurities

Nature of strained InAs three‐dimensional island formation and distribution on GaAs(100)

A. Madhukar, Q. Xie, P. Chen, and A. Konkar

Appl. Phys. Lett. 64, 2727 (1994); http://dx.doi.org/10.1063/1.111456 (3 pages) | Cited 111 times

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The substrate temperature and arsenic pressure dependence of the density of InAs three‐dimensional (3D) islands formed on GaAs(100) is found to exhibit a behavior that cannot be reconciled within the currently popular view of MBE growth. Rather, either an arsenic coverage induced strain enhanced In migration or strain dependent arsenic incorporation at islands, or both, appear to be operative. Plan‐view and cross‐sectional transmission electron microscopy, including the nature of the Moiré fringes, are used to obtain cluster size distribution and demarcation between size regime for coherent versus incoherent islands. The results point to the possibility of realizing a regular array of quantum dots made of coherently strained 3D islands of uniform size via growth on prepatterned substrates.
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68.55.-a Thin film structure and morphology

Observation of the D‐center in 6H‐SiC p‐n diodes grown by chemical vapor deposition

Michael S. Mazzola, Stephen E. Saddow, Philip G. Neudeck, V. K. Lakdawala, and Susan We

Appl. Phys. Lett. 64, 2730 (1994); http://dx.doi.org/10.1063/1.111457 (3 pages) | Cited 21 times

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The D‐center in 6H‐SiC is a boron‐related deep hole trap observed previously in LPE‐grown 6H‐SiC diodes. We report deep level transient spectroscopy (DLTS) measurements in which the D‐center signature is observed in high‐purity n‐ and p‐type epitaxial layers formed by chemical vapor deposition (CVD). An activation energy of 0.58 eV and a capture cross section between 1×10−14 cm2 and 3×10−14 cm2 was determined for this level. Even though the D‐center in these diodes is thought to arise from unintended trace contamination, we observed within the same diode a factor of twenty greater density of this level in the n‐type layer than in the p‐type layer, which is explained by a recently proposed site competition model for impurity doping during 6H‐SiC CVD growth.
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71.55.Ht Other nonmetals
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Josephson broadband spectroscopy to 1 THz

J. Edstam and H. K. Olsson

Appl. Phys. Lett. 64, 2733 (1994); http://dx.doi.org/10.1063/1.111458 (3 pages) | Cited 6 times

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We demonstrate the operation of a ‘‘Josephson Broadband Spectrometer’’ (JOBS) with a frequency range and bandwidth of 1 THz. The JOBS uses the inherent frequency tuning of the Josephson oscillations (f=2 eV/h) as a probe of the complex impedance environment, ZL(f), of the Josephson junction. Spectra taken of microstrip resonators (YBa2Cu3O7/SiO/Au) display up to nine harmonic resonances corresponding to a bandwidth of 1000 GHz. We find the surface resistance of YBa2Cu3O7 to scale as f2 over this frequency range, whereas the London penetration depth is frequency independent. The upper frequency limit of the measurement is set by the resonator loss whereas the JOBS presumably has an even larger intrinsic bandwidth.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
85.25.Cp Josephson devices
74.25.N- Response to electromagnetic fields

Magnetic and magneto‐optic properties of thick face‐centered‐cubic Co single‐crystal films

T. Suzuki, D. Weller, C.‐A. Chang, R. Savoy, T. Huang, B. A. Gurney, and V. Speriosu

Appl. Phys. Lett. 64, 2736 (1994); http://dx.doi.org/10.1063/1.111946 (3 pages) | Cited 22 times

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The present letter describes for the first time the magnetic and magneto‐optical properties of thick fcc cobalt single‐crystal films (≂1000‐Å thickness). The magneto‐crystalline anisotropy constants K1 and K2 are about −7.2×10 erg/cc and 2×10 erg/cc at 77 K, respectively. Both decrease in magnitude with increasing temperature in a range from 77 K to about 450 K. The easy axis is found to be 〈111〉. The polar Kerr angle for the fcc phase is much larger than that of the hcp phase by 0.1°–0.2° in a photon energy range from about 1 to 5 eV.
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75.50.Cc Other ferromagnetic metals and alloys
78.20.Ls Magneto-optical effects
75.60.-d Domain effects, magnetization curves, and hysteresis
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

New type of magnetocaloric effect: Implications on low‐temperature magnetic refrigeration using an Ericsson cycle

H. Takeya, V. K. Pecharsky, K. A. Gschneidner, and J. O. Moorman

Appl. Phys. Lett. 64, 2739 (1994); http://dx.doi.org/10.1063/1.111459 (3 pages) | Cited 26 times

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The low‐temperature, high magnetic field heat capacity (1.5 to 70 K and 0 to 9.85 T), dc and ac magnetic behaviors of the compound (Gd0.54Er0.46)AlNi show that field‐induced magnetic entropy change is significant and almost constant over the temperature region of ∼15 to ∼45 K. The resulting temperature dependence of the magnetocaloric effect, nearly constant over a 30+ K temperature range, is unprecedented (most magnetic materials have a caretlike shape temperature dependence). These data show that (Gd0.54Er0.46)AlNi can be used as an effective active magnetic regenerator material for an Ericsson‐cycle magnetic refrigerator, and could substitute for complex composite layered materials suggested earlier.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Cc Other ferromagnetic metals and alloys
65.40.Ba Heat capacity
65.20.-w Thermal properties of liquids
65.40.gd Entropy

Fabrication of a diamond field emitter array

Ken Okano, Kimihiko Hoshina, Masamori Iida, Satoshi Koizumi, and Tadao Inuzuka

Appl. Phys. Lett. 64, 2742 (1994); http://dx.doi.org/10.1063/1.111460 (3 pages) | Cited 72 times

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A diamond field emitter array has been fabricated. by Chemical vapor deposition. Diamond was grown on an inverted pyramidal‐shape Si substrate followed by removal of the substrate. The fabricated array was placed in a high vacuum pumping system with the pressure of ∼10−7 Torr and the emission current as a function of the anode voltage was measured. The distance between the tungsten anode and the diamond surface was held constant at 100 μm throughout the measurement. As a result, a current larger than 10−4 A was obtained for an anode voltage of 6 kV. A linear relationship in the Fowler–Nordheim plot indicated the existence of electron field emission from the fabricated diamond field emitter array.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.30.+y Surface double layers, Schottky barriers, and work functions
85.45.-w Vacuum microelectronics
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Nanosecond imaging study on laser ablation of liquid benzene

Yasuyuki Tsuboi, Hiroshi Fukumura, and Hiroshi Masuhara

Appl. Phys. Lett. 64, 2745 (1994); http://dx.doi.org/10.1063/1.111461 (3 pages) | Cited 15 times

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KrF excimer laser ablation of liquid benzene was studied by a nanosecond imaging technique. The ejection of a plume followed by remarkable transient morphological changes took place, which was directly observed over a wide range of the fluence. From imaging data, an ablation threshold was determined to be 100 mJ/cm2 and ablation behavior induced by electronic excitation of liquid molecules is considered. A delay time prior to the plume ejection is about 40±20 ns, while the remarkable morphological change ranges from sub‐μs to ms time regime.
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82.50.-m Photochemistry
81.15.Fg Pulsed laser ablation deposition
78.47.-p Spectroscopy of solid state dynamics
33.80.-b Photon interactions with molecules
FREE

Erratum: Second harmonic generation from SimGen superlattices [Appl. Phys. Lett. 63, 2324 (1993)]

D. J. Bottomley, G. Lupke, M. L. Ledgerwood, X. Q. Zhou, and H. M. van Driel

Appl. Phys. Lett. 64, 2748 (1994); http://dx.doi.org/10.1063/1.111995 (1 page) | Cited 4 times

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Abstract Unavailable
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Li Other semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
99.10.Cd Errata
FREE

Erratum: Dislocations and strain relief in compositionally graded layers [Appl. Phys. Lett. 62, 693 (1993)]

J. Tersoff

Appl. Phys. Lett. 64, 2748 (1994); http://dx.doi.org/10.1063/1.111996 (1 page) | Cited 6 times

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Abstract Unavailable
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68.55.-a Thin film structure and morphology
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.Lk Linear defects: dislocations, disclinations
99.10.Cd Errata
FREE

Erratum: Theory of zone‐folded optical transitions in semiconductor superlattices [Appl. Phys. Lett. 63, 3253 (1993)]

M. E. Lazzouni and L. J. Sham

Appl. Phys. Lett. 64, 2748 (1994); http://dx.doi.org/10.1063/1.111997 (1 page)

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Abstract Unavailable
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.-w Optical properties of specific thin films
99.10.Cd Errata
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