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  • 1
    Electronic Resource
    Electronic Resource
    Effect of ion energy on Sn donor activation and defect production in molecular beam epitaxy GaAs doped with Sn ions during growth (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4375-4381 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The production of electrically active defect centers in molecular beam epitaxy (MBE) GaAs irradiated with low energy (50–500 eV) Sn ions during growth has been investigated as a function of ion energy. GaAs was doped n type during growth with a specially designed Sn focused ion beam column mounted on a MBE growth chamber. The 77 and 300 K Hall mobility and carrier concentration of the GaAs depended strongly on the ion energy, thus providing a sensitive measure of the concentration of ion-induced acceptorlike defect centers. The material was found to be nonconducting for ion energies greater than 200 eV, while a systematic decrease in the acceptor concentration, and consequent increase in the mobility, was observed as the ion energy was decreased below this value. A peak mobility of 90 000 cm2 V−1 s−1 at a carrier concentration of 1×1014 cm−3 was achieved (at 60 K) which is in excess of that obtained in other reports of ion-doped GaAs. A similar dependence on ion energy was found in the 4.2 K photoluminescence spectra of the ion-doped GaAs, characterized by the appearance of a broad acceptor level peak and a decrease in the overall luminescent intensity with increasing ion energy. The lowest energy doped samples provided high quality spectra with narrow linewidths comparable with thermal (Si) doped material. Using the above data, a mechanism is proposed for the production of acceptor centers in this system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354405
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  • 2
    Electronic Resource
    Electronic Resource
    Electron transport across a wide AlGaAs barrier (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 5606-5621 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An experimental and theoretical study has been made of electron transport over a wide AlGaAs barrier with graded interfaces sandwiched between GaAs contact layers. The width of the central barrier region was varied between 700 and 2100 A(ring). Two series of samples with nominally identical structures but from different sources were investigated. Extensive measurements of both the voltage and temperature dependence of the current were made, as well as measurements of capacitance and magnetoresistance. Drift-diffusion thermionic emission theory has been used to interpret the data. Both numerical and analytical solutions of the model have been developed and were found to be in good agreement with each other. The presence of space charge in the barrier region, which has the effect of increasing the barrier height, was seen to be crucial to an understanding of the data. When the effect of space charge was included in the model good agreement was obtained between theory and experiment for electric fields up to 10 kV cm−1. The numerical solution required only one adjustable parameter, namely the value of the space-charge density. The parameters used in the analytical model were all derived from the experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354222
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetization reversal and magnetoresistance in a lateral spin-injection device (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 6682-6685 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the magnetization reversal and magnetoresistance (MR) behavior of a lateral spin-injection device. The device consists of a two-dimensional electron gas (2DEG) system in an InAs quantum well and two ferromagnetic (Ni80Fe20) contacts: an injector (source) and a detector (drain). Spin-polarized electrons are injected from the first contact and propagating through InAs are collected by the second contact. By engineering the shape of the permalloy film distinct switching fields (Hc) from the injector and the collector have been observed by scanning Kerr microscopy and MR measurements. Magneto-optic Kerr effect (MOKE) hysteresis loops demonstrate that there is a range of magnetic field (20–60 Oe), at room temperature, over which magnetization in one contact is aligned antiparallel to that in the other. The MOKE results are consistent with the variation of the magnetoresistance in the spin-injection device. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370504
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  • 4
    Electronic Resource
    Electronic Resource
    Scanning noninvasive voltage probe operating at 4.2 K (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 2100-2105 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A noninvasive voltage probe, consisting of a one-dimensional channel, has been fabricated within a modulation doped GaAs/AlGaAs heterostructure. With precision piezoelectric scanning equipment this probe has been brought to within 14 nm of a semiconductor device which includes surface gates and a 300 nm deep two-dimensional electron gas. Measurements of voltages applied to these conducting layers have been made at room temperature and at 4.2 K using the sensitive conductance of the one-dimensional channel. A voltage resolution of 0.48 mV has been observed at 4.2 K. Probe conductance measurements have also been made as a function of probe–sample separation. The conductance–separation data were fitted using a simple parallel plate capacitor model and a height resolution of 4 nm was calculated. Images of the sample layers have been obtained and a lateral resolution of 760 nm observed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1351839
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  • 5
    Electronic Resource
    Electronic Resource
    Theory of magnetic-field enhancement of surface-field terahertz emission (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 2104-2106 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a theoretical treatment of surface–field THz generation in semiconductors, which explains the power enhancement observed when a magnetic field is applied. Our model consists of two parts: a Monte Carlo simulation of the dynamics of carriers generated by a subpicosecond optical pulse, and a calculation of the resulting THz radiation emitted through the semiconductor surface. The magnetic field deflects the motion of the carriers, producing a component of the THz dipole parallel to the surface. This causes the power transmitted through the surface to be increased by more than one order of magnitude. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1433187
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  • 6
    Electronic Resource
    Electronic Resource
    A simple lateral transport device of strongly interacting electron and hole layers (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1603-1605 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated a GaAs device containing independently contacted electron and hole layers with a separation of 14 nm. The device processing avoids the use of self-aligned contacts and is, therefore, greatly simplified. Only basic processing facilities are required, and leakage problems typical of self-aligned contacts are prevented. The resulting increased device yield overcomes a technological barrier, which has so far limited the experimental research of the system. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123630
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  • 7
    Electronic Resource
    Electronic Resource
    Electrically active defect centers induced by Ga+ focused ion beam irradiation of GaAs(100) (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 576-578 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electronic nature of defect centers induced by 30 keV Ga+ focused ion beam irradiation of GaAs(100) has been studied in situ by scanning tunneling spectroscopy (STS). The defect centers were identified as electron traps lying below the surface state conduction band, each with an active area of approximately 20 nm2. An areal ion beam dose of 1×1013 cm−2 was sufficiently low that no significant surface sputtering was observed by topographic imaging which suggests that the features observed by STS are not related to gross physical damage. Spatial STS measurements also allow a lateral profile of a focused ion beam patterned line to be determined accurately, thereby setting a resolution limit on the direct write technique for nanoscale lithography. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123150
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  • 8
    Electronic Resource
    Electronic Resource
    Contact resistances of NiGeAu, PdGeTiPt, and TiPd ohmic contacts to GaAs and their temperature dependence from 4.2 to 350 K (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 4197-4199 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The specific contact resistance (rc) of NiGeAu and PdGeTiPt ohmic contacts to n-GaAs and TiPd and PdGeTiPt ohmic contacts to p+-GaAs were determined as a function of temperature between 4.2 and 350 K. The low rc obtained for some of the contacts at 4.2 K implies that much of the total contact resistance measured at 4.2 K in two-dimensional electron gas structures lies across the n–n heterojunction(s) in series with the metal semiconductor junction. Although NiGeAu contacts have a lower contact resistance to n-GaAs, PdGeTiPt contacts, which have much better edge definition, can be substituted for the NiGeAu when they are properly annealed. Also, contacts with low rc values at 4.2 K can be made to p+-GaAs using either TiPd or properly annealed PdGeTiPt contacts. The rc versus temperature curves for the TiPd and alloyed NiGeAu contacts fit the field emission model. The other contacts have a larger temperature dependence suggesting that tunneling occurs via thermionic field emission directly through the barrier or via defect states. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116984
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  • 9
    Electronic Resource
    Electronic Resource
    Resonant tunneling between parallel, two-dimensional electron gases: A new approach to device fabrication using in situ ion beam lithography and molecular beam epitaxy growth (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 1827-1829 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using the techniques of in situ focused ion beam lithography and molecular beam epitaxy regrowth high quality, patterned back gate, double quantum well devices have been fabricated. Independent ohmic contacts were made to the two two-dimensional electron gases (2DEGs) using a "selective depletion'' scheme, and using further gates the carrier densities in each well were controlled. Resonant tunneling between the two electron gases was observed as a function of carrier density in each 2DEG, and as a function of the bias applied between the two wells. Extremely large peak-to-valley ratios were observed, resulting from removal of unwanted parallel tunneling paths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111768
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  • 10
    Electronic Resource
    Electronic Resource
    Independent contacting to electron layers in a double quantum well system using Pd-Ge shallow ohmic contacts (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 851-853 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel recess technique is used to produce reliable Pd-Ge ohmic contacts to GaAs/AlGaAs high mobility two-dimensional electron gas (2DEG) systems, operating down to cryogenic temperatures. By altering the depth of the recess the diffusion length of the contacts is found to be less than 20 nm. Pd-Ge shallow ohmic contacts were also used for forming independent contacts to two 2DEGs in a double quantum well structure where the 2DEGs are separated by only a 20 nm AlxGa1−xAs(x=0.3) barrier. Tunnel current measurements and magnetoresistance analysis confirmed that the layers could be probed individually and that the carrier densities and mobilities of the separate layers could be accurately determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112180
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