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28 Sep 1992

Volume 61, Issue 13, pp. 1481-1604

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High‐field electron velocity measurement in GaAs/AlGaAs multiple‐quantum wells

Naoteru Shigekawa, Tomofumi Furuta, Kunihiro Arai, and Masaaki Tomizawa

Appl. Phys. Lett. 61, 1555 (1992); http://dx.doi.org/10.1063/1.107494 (3 pages) | Cited 1 time

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We measured the electron velocity versus electric field (v‐E) relationships for GaAs/AlGaAs multiple quantum wells with different well‐layer thicknesses (50, 100, and 200 Å). No clear dependences on the well thickness have been observed in the measured v‐E’s, which indicate that the confinement of electrons in well layers does not induce strong effects on the momentum relaxation and the energy loss rate. The results of the measurement were also compared with those derived by the Monte Carlo calculation, and a remarkable discrepancy between measured and calculated results was found in the well thickness dependence of the electron peak velocity.
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73.50.Fq High-field and nonlinear effects
73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Optical detection of growth oscillations from high vacuum up to low‐pressure metalorganic vapor phase epitaxy like conditions

K. Deppert, J. Jönsson, and L. Samuelson

Appl. Phys. Lett. 61, 1558 (1992); http://dx.doi.org/10.1063/1.107495 (3 pages) | Cited 7 times

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We report optical, real‐time detection of growth oscillations for pressures up to low‐pressure metalorganic vapor phase epitaxy (LP‐MOVPE) like conditions. The measurements were performed using the reflectance difference technique during epitaxial growth of GaAs in a vacuum chemical epitaxy (VCE) chamber in which the LP‐MOVPE conditions were obtained by adding hydrogen. Growth oscillations could still be obtained over a wide range of V/III ratios at pressures in the mbar range. Under LP‐MOVPE conditions we could observe oscillation amplitudes comparable to those found under VCE conditions. Furthermore, the occurrence of oscillations when hydrogen is introduced shows that the layer‐by‐layer growth is not affected by the presence of hydrogen. These results seem to open the way for the in situ detection of growth oscillations even in conventional MOVPE systems.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.-a Thin film structure and morphology
78.47.-p Spectroscopy of solid state dynamics

Mesa stripe transverse injection laser in HgCdTe

P. Bouchut, G. Destefanis, J. Bablet, A. Million, T. Colin, and M. Ravetto

Appl. Phys. Lett. 61, 1561 (1992); http://dx.doi.org/10.1063/1.107496 (3 pages) | Cited 5 times

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In this letter, we report the fabrication and operation of narrow stripe, transverse injection, HgCdTe lasers. The double heterostructure of the laser was grown by molecular beam epitaxy on (111) CdZnTe substrate. The n‐type base was extrinsically indium doped but the upper p‐type confining layer was only doped by deviation from stoichiometry. Laser emissions at 3.40 and 3.56 μm were obtained at 78 K under pulsed current conditions. Threshold current as low as 48 mA and differential quantum efficiency as high as 4.2% were achieved. Over 60 K threshold current has an exponential increase with temperature and a T0 parameter of 8 K.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation
85.60.Jb Light-emitting devices

Novel approach to CuInSe2‐based thin‐film photovoltaic cells

Shalini Menezes

Appl. Phys. Lett. 61, 1564 (1992); http://dx.doi.org/10.1063/1.107497 (3 pages) | Cited 2 times

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A new n‐CuInSe2‐based cell has been constructed with a concerted effort at the synthesis of n‐CuInSe2 thin‐film absorber and the electrochemical conversion of the CuInSe2 surface to a semi‐insulating, lattice‐matched CuInxSeyIz transition layer and a semiconducting p‐CuISe3 window. The CuISe3 layer can be anodically formed on n‐type or p‐type CuInSe2; it forms a rectifying p‐n junction with n‐CuInSe2 and an ohmic contact with p‐CuInSe2. This cell obviates some of the prevailing concerns with the p‐CuInSe2/n‐CdS cell while retaining the thin‐film attributes of the radiation‐tolerant CuInSe2.
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84.60.Jt Photoelectric conversion
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ga II-VI semiconductors
81.65.-b Surface treatments

Theory of phonon‐limited mobility in a delta‐doped quantum well

Doyeol Ahn

Appl. Phys. Lett. 61, 1567 (1992); http://dx.doi.org/10.1063/1.107498 (3 pages) | Cited 2 times

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The electron mobility at room temperature due to phonon scatterings in a delta‐doped quantum well is calculated theoretically. A many‐body formalism is used to obtain self‐energy terms for electron‐phonon interactions. It is predicted that the electron mobility is reduced significantly by several factors with increasing delta‐doping in a quantum well.
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73.50.Bk General theory, scattering mechanisms
73.50.Dn Low-field transport and mobility; piezoresistance
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors

Si‐GaAs(001) superlattices

L. Sorba, G. Bratina, A. Franciosi, L. Tapfer, G. Scamarcio, V. Spagnolo, and E. Molinari

Appl. Phys. Lett. 61, 1570 (1992); http://dx.doi.org/10.1063/1.107499 (3 pages) | Cited 7 times

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Si‐GaAs(001) superlattices have been grown by molecular beam epitaxy. X‐ray interference measurements and Raman spectroscopy studies in the acoustic range for (Si)2(GaAs)28 and (Si)3(GaAs)50 superlattice structures demonstrate that pseudomorphic growth conditions were achieved. Raman data in the optical range show large (∼50–70 cm−1) confinement‐ and strain‐induced shifts of the Si‐like optical modes.
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78.30.-j Infrared and Raman spectra
78.66.-w Optical properties of specific thin films
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Remotely‐doped superlattices in wide parabolic GaAs/AlxGa1−xAs quantum wells

J. H. Baskey, A. J. Rimberg, Scott Yang, R. M. Westervelt, P. F. Hopkins, and A. C. Gossard

Appl. Phys. Lett. 61, 1573 (1992); http://dx.doi.org/10.1063/1.107500 (3 pages) | Cited 4 times

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Using the digital alloy technique, a series of high‐mobility remotely doped GaAs/AlGaAs coupled multiple quantum well structures have been produced by the superposition of a wide parabolic quantum well and a square superlattice potential. Structures containing up to twenty superlattice periods with low temperature Hall mobilities from 23 000 to 100 000 cm2/V s have been produced. Fourier analysis of low field Shubnikov–de Haas oscillations, capacitance‐voltage and Hall measurements of a 200 Å period superlattice in a 1600 Å wide parabolic well indicate the occupation of four superlattice periods with subband spacings in good agreement with theory.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Low‐frequency noise in InP‐based NnPnN double heterojunction bipolar transistors

Y. K. Su, S. C. Shei, and C. H. Chen

Appl. Phys. Lett. 61, 1576 (1992); http://dx.doi.org/10.1063/1.107501 (3 pages) | Cited 1 time

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This letter deals with the low‐frequency noise in an InGaAs(P)/InP double heterojunction bipolar transistor at room temperature. The recombination is mainly responsible for the noise. The current dependence of the base noise with floating collector was of the form IB3 and the shot noise of base current corresponding to 3.2×10−24 A2/Hz for f=10 Hz. The current dependence of the collector noise with high frequency short circuited was of the form Ic1.55 and the shot noise of collector current corresponding to 3.2×10−24 A2/Hz for f=10 Hz.
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85.30.Pq Bipolar transistors
73.50.Td Noise processes and phenomena
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Two‐dimensional electron gas effects in the electromodulation spectra of a pseudomorphic Ga0.78Al0.22As/In0.21Ga0.79As/GaAs modulation‐doped quantum well structure

Yichun Yin, H. Qiang, Fred H. Pollak, Dwight C. Streit, and Michael Wojtowicz

Appl. Phys. Lett. 61, 1579 (1992); http://dx.doi.org/10.1063/1.107502 (3 pages) | Cited 39 times

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We have studied the electroreflectance and photoreflectance spectra from a pseudomorphic Ga0.78Al0.22As/In0.21Ga0.79As/GaAs modulation‐doped quantum well (MDQW) structure in the temperature range 79<T<304 K. The features from the InGaAs MDQW can be accounted for on the basis of a two‐dimensional density of states and a Fermi level filling factor. A detailed line shape fit makes it possible to evaluate the Fermi energy, and hence the two‐dimensional electron gas concentration (Ns), as well as other important parameters of the structure. Our value for Ns is in good agreement with a Hall measurement.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

Defect‐assisted resonant tunneling: A theoretical model

D. Stievenard, X. Letartre, and M. Lannoo

Appl. Phys. Lett. 61, 1582 (1992); http://dx.doi.org/10.1063/1.107503 (3 pages) | Cited 6 times

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Defects are often taken as the cause of deviations in the current‐voltage characteristics of heterostructures such as barrier or double barrier, and the so‐called defect‐assisted tunneling effect has been assumed to occur in certain cases. We present an analytical analysis of the tunneling effect which occurs through a barrier and which is assisted by an energy level associated with a defect. Moreover, we show that a negative differential resistance can occur using a single barrier in which a defect is located.
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73.40.Gk Tunneling
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
71.55.Eq III-V semiconductors

Fermi level pinning in low‐temperature molecular beam epitaxial GaAs

H. Shen, F. C. Rong, R. Lux, J. Pamulapati, M. Taysing‐Lara, M. Dutta, E. H. Poindexter, L. Calderon, and Y. Lu

Appl. Phys. Lett. 61, 1585 (1992); http://dx.doi.org/10.1063/1.107504 (3 pages) | Cited 25 times

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The Fermi level position in low temperature (LT) GaAs has been studied by photoreflectance (PR). By etching the LT‐GaAs to a different thickness, we find the Fermi level in the as‐grown as well as the annealed LT‐GaAs is firmly pinned. The pinning position, however, occurs at different energies: 0.47 eV below the conduction band edge for the as‐grown samples and 0.65 eV below the conduction band edge for the annealed samples. The pinning in the as‐grown LT‐GaAs is believed to be the result of a high degree of charge compensation by deep levels, while the pinning in the annealed LT‐GaAs is due to the depletion of carriers by the Schottky barrier at the metallic As precipitates. From the measured Fermi level and ionization ratio of As antisites, the (0/+) donor level of the As antisite in LT‐GaAs is, for the first time, determined at Ec−0.57 eV.
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73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.30.+y Surface double layers, Schottky barriers, and work functions

Dissociation energies of acceptor‐hydrogen complexes in InP

S. J. Pearton, W. S. Hobson, and C. R. Abernathy

Appl. Phys. Lett. 61, 1588 (1992); http://dx.doi.org/10.1063/1.107505 (3 pages) | Cited 20 times

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The dissociation energies of Zn‐H, Cd‐H, and Mg‐H complexes in p‐InP have been determined from the reactivation kinetics of these passivated dopants in reverse‐biased Au Schottky diodes. The reactivation process is first order under these conditions, yielding thermal dissociation energies of 1.20±0.10 eV for Zn acceptors, 1.40±0.10 eV for Cd acceptors, and 1.35±0.10 eV for Mg acceptors. These results are consistent with the model in which the hydrogen passivates the acceptor by attaching to a neighboring P atom, leaving the acceptor essentially threefold coordinated. They also indicate that acceptor‐hydrogen retrapping during cool down after epitaxial growth of p‐InP layers is the primary cause of apparently stable acceptor passivation seen in such layers.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.60.Dv Thermal stability; thermal effects
73.61.Ey III-V semiconductors
72.80.Ey III-V and II-VI semiconductors

Single‐electron Coulomb blockade in a nanometer field‐effect transistor with a single barrier

Stephen Y. Chou and Yun Wang

Appl. Phys. Lett. 61, 1591 (1992); http://dx.doi.org/10.1063/1.107506 (3 pages) | Cited 9 times

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The first experimental study of a new nanometer field‐effect transistor with a single barrier in its one‐dimensional channel is presented. At low temperatures and as charge density in the channel was varied, nine reproducible periodic oscillations of conductance, in addition to 2e2/h conductance plateaus, were observed before the onset of the first 2e2/h conductance plateau. It was found experimentally that each conductance oscillation corresponds to the Coulomb blockade of a single electron in the one‐dimensional channel. A model that describes the operation of the new single electron transistor is suggested.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.45.-d Collective effects
72.15.Nj Collective modes (e.g., in one-dimensional conductors)
73.40.Gk Tunneling

Transient response of a high Tc superconducting thin film

Shirshak K. Dhali and Lei Wang

Appl. Phys. Lett. 61, 1594 (1992); http://dx.doi.org/10.1063/1.107507 (3 pages) | Cited 4 times

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The transient response of a YBCO thin film to a current pulse is reported. The measured rate of change of resistance across the superconductor is consistent with the thermal propagation of a normal region in a thin superconducting film. It appears that the normal region occurs at an ohmic contact and propagates across the length of the film, thus switching the film from its superconducting state to its normal state. The rate of resistance change shows a strong dependence on the bias temperature and current.
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74.70.-b Superconducting materials other than cuprates
74.25.N- Response to electromagnetic fields
85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices

YBa2Cu3O7 nanobridges fabricated by direct‐write electron beam lithography

J. R. Wendt, J. S. Martens, C. I. H. Ashby, T. A. Plut, V. M. Hietala, C. P. Tigges, D. S. Ginley, M. P. Siegal, J. M. Phillips, and G. K. G. Hohenwarter

Appl. Phys. Lett. 61, 1597 (1992); http://dx.doi.org/10.1063/1.107508 (3 pages) | Cited 11 times

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A direct method for nondamaging, nanometer‐scale patterning of high Tc superconductor thin films is presented. We have fabricated superconducting nanobridges in high‐quality, epitaxial thin‐film YBa2Cu3O7 (YBCO) by combining direct‐write electron beam lithography and an improved aqueous etchant. Weak links with both length and width dimensions less than 20 nm have exhibited critical currents at 77 K of 4–20 μA and IcRn products of 10–100 μV which compare favorably with results for other YBCO junction technologies. We have used this technique in the fabrication of a shock‐wave pulse former as an initial demonstration of its applicability to monolithic superconductive electronics.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.-b Surface treatments
85.25.Cp Josephson devices
74.70.-b Superconducting materials other than cuprates
74.25.N- Response to electromagnetic fields

Evaporated CoPt alloy films with strong perpendicular magnetic anisotropy

C.‐J. Lin and G. L. Gorman

Appl. Phys. Lett. 61, 1600 (1992); http://dx.doi.org/10.1063/1.107509 (3 pages) | Cited 43 times

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CoPt alloy films with large perpendicular magnetic anisotropy, perpendicular coercivity, and saturated perpendicular remanence are reported. These films were fabricated by e‐beam evaporation at substrate temperatures near 200 °C and above. Well‐(111)‐textured Pt underlayers are shown to dramatically increase the perpendicular magnetic anisotropy of CoPt alloy films. The large perpendicular magnetic anisotropy is shown to be strongly related to good CoPt(111) texture, and not to the ordered tetragonal Co50Pt50 phase.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Cc Other ferromagnetic metals and alloys
75.30.Gw Magnetic anisotropy
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Study of diffusion of a fluorinated hydrocarbon in ion beam irradiated poly(styrene) by nuclear resonance analysis

Kenji Umezawa, Walter M. Gibson, John T. Weltch, Peiguang Zhou, Qihua Xu, and Harry L. Frisch

Appl. Phys. Lett. 61, 1603 (1992); http://dx.doi.org/10.1063/1.107510 (2 pages) | Cited 1 time

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The diffusion of a fluorinated hydrocarbon into 30 keV‐H+ irradiated glassy poly(styrene) (PS) was studied by using nuclear resonance reaction analysis. The diffraction coefficient and front velocity for diffusing a particular fluorinated hydrocarbon, 3, 5‐bis (trifluoromethyl) aniline (TFMA) in PS (MW=400 000) are dramatically decreased on irradiation with 5×1013–1×1014 atoms/cm2 at 22.5 °C. These ion beam irradiation effects are similar to temperature effects on diffusion. A possible application of the observed effect is the control of diffusion of a vapor into cross‐linked polymer glasses by means of ion beam implantation techniques. It is our belief that this is the first report of this phenomena due to the effects of ion beam irradiation.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
66.30.J- Diffusion of impurities
61.80.Jh Ion radiation effects
61.72.up Other materials
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