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13 Sep 1993

Volume 63, Issue 11, pp. 1453-1587

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Crystallographic selective growth of GaAs by atomic layer epitaxy

Hideo Isshiki, Yoshinobu Aoyagi, Takuo Sugano, Sohachi Iwai, and Takashi Meguro

Appl. Phys. Lett. 63, 1528 (1993); http://dx.doi.org/10.1063/1.110738 (3 pages) | Cited 11 times

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We found high crystallographic selectivity in atomic layer epitaxy (ALE) growth of GaAs, in comparison with other epitaxial growth methods. In the temperature dependence of the GaAs growth rate, no GaAs growth on the GaAs (111)A and (110) planes was observed in the high temperature range under the condition of GaAs ALE growth on GaAs (100) plane. Also we discussed the mechanism of GaAs growth selectivity, which was believed to be caused by growth limitation due to As desorption. Due to the self‐limiting effect and the high selectivity of ALE growth, trapezoidal‐shaped GaAs/AlGaAs quantum wire structures, with 20 nm thickness and 50 nm width, were successfully realized.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Reversible changes of the charge state of donor/hydrogen complexes initiated by hole capture in silicon

C. H. Seager and R. A. Anderson

Appl. Phys. Lett. 63, 1531 (1993); http://dx.doi.org/10.1063/1.110739 (3 pages) | Cited 11 times

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The effect of light‐injected holes on phosphorus/hydrogen pairs has been examined in silicon. Previous studies have shown that light soaking appears to debond H from phosphorus, thereby returning it to the positive charge state. Here, we demonstrate that this charge state change is partially reversible if samples are held in electronic equilibrium for periods of hours to days. Since this recovery process can be delayed for days by depleting the light‐soaked region, it appears that freed hydrogen is not merely returning to donors, but that the original hole capture event is merely creating a different charge state of the P⋅H pair. We also demonstrate that the kinetics of the hole‐induced conversion process is markedly different in depletion than in zero bias and suggest that this is due to the presence of the recovery process which can only occur in the presence of free electrons.
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71.55.Cn Elemental semiconductors
61.72.uf Ge and Si
72.80.Cw Elemental semiconductors

Intrasubband plasmons in delta‐doped InGaAs single quantum wells

L. H. Peng and C. G. Fonstad

Appl. Phys. Lett. 63, 1534 (1993); http://dx.doi.org/10.1063/1.110740 (3 pages) | Cited 4 times

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Polarization‐resolved infrared techniques have been applied to study the optical properties of the quasi‐two‐dimensional electron gas in doped InGaAs quantum wells and to show that inter‐ and intrasubband processes can be distinguished by their polarization sensitivity. Distinct excitations of inter‐ and intrasubband transitions at the Γ(q=k=0) point in delta‐doped narrow InGaAs/AlAs single quantum wells were resolved through the use of quantum well structures designed to increase their energy difference and thus diminish the coupling between these two processes. Longitudinal qz intrasubband plasmons were observed at 1550 cm−1 and were excited by transverse‐magnetic (TM) polarized light; the intersubband transitions occurred at around 4000 cm−1 and were both transverse‐electric (TE) and TM polarization active.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Heterostructure bipolar transistor with enhanced forward diffusion of minority carriers

Serge Luryi, Anatoly A. Grinberg, and Vera B. Gorfinkel

Appl. Phys. Lett. 63, 1537 (1993); http://dx.doi.org/10.1063/1.110741 (3 pages) | Cited 2 times

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We consider the minority transport in a heterostructure bipolar transistor whose base band gap narrows down toward the collector in N discontinuous steps. Assuming that the potential energy drop at each step is sufficiently large to prevent the reverse flow of minority carriers, we show that the total base propagation delay τ is shorter by a factor of N compared to the diffusive delay in a flat base of the same width. Moreover, if the length of each step is sufficiently narrow, then for large N the magnitude ‖α‖ of the base transport factor α=‖α‖exp(−iωτ) decreases so slowly with increasing frequency ω that it becomes feasible to obtain an active behavior of the transistor above its own conventional cutoff frequencies.
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85.30.Pq Bipolar transistors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
84.30.Ng Oscillators, pulse generators, and function generators
72.30.+q High-frequency effects; plasma effects

Improved strain analysis in semiconductor crystals by x‐ray diffractometry enhanced with ultrasound

E. Zolotoyabko, B. Sander, Y. Komem, and B. Kantor

Appl. Phys. Lett. 63, 1540 (1993); http://dx.doi.org/10.1063/1.110742 (3 pages) | Cited 5 times

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A new method that combines double‐crystal x‐ray diffraction with high‐frequency ultrasonic excitation is proposed in order to study small strains in semiconductor crystals. Ultrasound having a wavelength a little less than the x‐ray extinction length affects the diffraction profile very near the Bragg position and, therefore, permits the detection of very small profile broadenings caused by lattice distortions. Experimental results obtained for fresh etched, boron‐doped (001)Si samples, using (004)‐reflection and Cu Kα radiation, have shown the presence of microstrains with the mean value of 〈Δd/d〉=5×10−6. Such small lattice distortion cannot be measured by standard double‐crystal diffractometry without ultrasound.
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61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
62.20.-x Mechanical properties of solids
43.35.Pt Surface waves in solids and liquids

Beryllium δ doping studies in InP and Ga0.47In0.53As during metalorganic molecular beam epitaxy

Dan Ritter, R. A. Hamm, M. B. Panish, and M. Geva

Appl. Phys. Lett. 63, 1543 (1993); http://dx.doi.org/10.1063/1.110743 (3 pages) | Cited 3 times

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A secondary ion mass spectroscopy study of δ and bulk doped layers demonstrates that the incorporation efficiency of Be in Ga0.47In0.53As and InP during metalorganic molecular beam epitaxy is much lower than unity. This effect is attributed to the removal of Be atoms from the surface by the organic gases in the growth chamber. The upper limit for δ doping of Ga0.47In0.53As before the onset of diffusion is 7×1012 cm−2, and in InP it is less than 5×1011 cm−2.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Crystallized mixed‐phase silicon films for thin film transistors on glass substrates

Apostolos T. Voutsas and Miltiadis K. Hatalis

Appl. Phys. Lett. 63, 1546 (1993); http://dx.doi.org/10.1063/1.110744 (3 pages) | Cited 14 times

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The low temperature crystallization of mixed‐phase silicon films deposited by low pressure chemical vapor deposition was investigated. The mixed phase consists of crystalline regions embedded in an amorphous matrix, with the crystalline fraction being a function of the deposition temperature and the deposition rate. In this material, the nucleation rate of new crystallites during annealing is higher than in a completely amorphous film, resulting in a shorter crystallization time and a smaller average grain size. To compensate for the reduction in the grain size, a composite structure was proposed consisting of two successive layers; a mixed‐phase layer and an amorphous layer. Crystallized mixed‐phase films were used for the fabrication of polysilicon thin film transistors on new Corning (Code 1735) glass substrates at a maximum processing temperature of 560 °C. A field‐effect mobility of 20 cm2/V s and a threshold voltage of 5.1 V were obtained even before hydrogenation.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
85.30.Tv Field effect devices

Synthesis of luminescent silicon clusters by spark ablation

Winston A. Saunders, Peter C. Sercel, R. B. Lee, Harry A. Atwater, Kerry J. Vahala, Richard C. Flagan, and Ernesto J. Escorcia‐Aparcio

Appl. Phys. Lett. 63, 1549 (1993); http://dx.doi.org/10.1063/1.110745 (3 pages) | Cited 19 times

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The synthesis of luminescent nanometer‐scale Si clusters by spark ablation from a crystalline Si substrate is described. The cluster source, described in the text, generates clusters in a flowing Ar stream at atmospheric pressure. Electron microscopy reveals that the clusters have diameters in the 2–4 nm size range. The luminescence spectra of the clusters, similar to that of porous Si, are presented.
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78.55.Hx Other solid inorganic materials
81.10.Bk Growth from vapor
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
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Photoinduced charge transfer and charge carrier generation in polysilane films containing C60 molecules

R. G. Kepler and P. A. Cahill

Appl. Phys. Lett. 63, 1552 (1993); http://dx.doi.org/10.1063/1.110746 (3 pages) | Cited 29 times

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We have studied charge carrier generation and transport in poly(methylphenylsilane) films containing C60 molecules, and have found that the quantum efficiency for carrier generation is increased by more than an order of magnitude over poly(methylphenylsilane) films not containing C60 and that hole transport is unaffected. We also measured the electroabsorption spectrum of the composite films and found no evidence for charge transfer transitions. We conclude that electrons are transferred from poly(methylphenylsilane) to C60 molecules that have been excited to their lowest energy absorption band at about 2 eV.  
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ph Polymers; organic compounds

Monolithic optoelectronic transistor: A new smart‐pixel device

B. F. Aull, K. B. Nichols, P. A. Maki, S. C. Palmateer, E. R. Brown, and T. A. Lind

Appl. Phys. Lett. 63, 1555 (1993); http://dx.doi.org/10.1063/1.110747 (3 pages) | Cited 9 times

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A new optical switching and logic device, the monolithic optoelectronic transistor (MOET), is demonstrated. The MOET is an integrated circuit consisting of a p‐i‐n photodiode, a resonant tunneling diode, a multiple‐quantum‐well modulator, and a field‐effect transistor. The device can function as an optical inverter or NOR gate. Present devices switch at an input optical power of 12.5 μW and have a large‐signal optical gain exceeding ten. The advantages of the MOET include abrupt switching thresholds, saturated ‘‘on’’ and ‘‘off’’ states, and nonlatching operation.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.82.Gw Other integrated-optical elements and systems
85.60.-q Optoelectronic devices

Positively charged states of a hydrogen atom in p‐type InP

Hoon Young Cho, Won Chel Choi, and Suk‐Ki Min

Appl. Phys. Lett. 63, 1558 (1993); http://dx.doi.org/10.1063/1.110748 (3 pages) | Cited 4 times

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It has been demonstrated that atomic hydrogen drifts as a charged state in p‐type InP and the presence of a high‐electric field strongly affects the dissociation of the hydrogen‐acceptor complex. During reverse‐bias anneal experiments on the n+‐p diode, it is confirmed that a charged hydrogen is accelerated out the high‐field region below the breakdown voltage. The dissociation frequencies dependent on the applied bias voltage increase from 5.6×10−6 to 2.3×10−5 s−1 at 150 °C as the bias voltage is increased from 3 to 9 V. The dissociation energies calculated from the first‐order kinetics are in the ranges of 1.58–1.40 eV, at 3–7 V annealing. It is proposed that atomic hydrogen in Zn‐doped p‐type InP exposed to the plasma hydrogen could be positively charged and strongly passivates the charged Zn acceptor, and also the hydrogen of the hydrogen‐Zn acceptor complex can be released with the help of minority carriers or/and the loss of the charged hydrogen atom by the electric field.
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71.55.Eq III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.uj III-V and II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors

Improved process for high‐Tc superconducting step‐edge junctions

J. Z. Sun, W. J. Gallagher, A. C. Callegari, V. Foglietti, and R. H. Koch

Appl. Phys. Lett. 63, 1561 (1993); http://dx.doi.org/10.1063/1.110749 (3 pages) | Cited 33 times

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We have developed a process for the fabrication of YBaCuO high‐Tc junctions based on the step‐edge weak‐link concept. The process emphasizes the creation of sharp and straight step edges on a substrate, and the restoration of oxygen content for superconducting materials at the step edges. A diamond‐like carbon film is used as an ion milling mask for the creation of steps on substrates such as LaAlO3 and SrTiO3. Room‐temperature plasma oxidation is shown to be effective in restoring Tc from processing related degradation for grains residing at the step edge. Using this process, dc SQUIDs were fabricated with 77 K electrical performances matching, and in certain cases exceeding, similar SQUIDs made using bicrystal‐based tilt‐boundary weak‐link junctions.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
85.25.Cp Josephson devices
74.72.-h Cuprate superconductors

Measurement of parametric interactions in YBa2Cu3O7−x step edge junctions

Aron Z. Kain and H. R. Fetterman

Appl. Phys. Lett. 63, 1564 (1993); http://dx.doi.org/10.1063/1.110750 (3 pages)

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We have fabricated and tested series arrays of YBa2Cu3O7−x (YBCO) step edge junctions for four photon parametric effects at 10 GHz. The series array of 25 junctions shows a 10 dB increase in reflected signal power as the pump power is increased at 10 K. At 50 K the reflected signal power shows a 3 dB increase. The reflected power at the characteristic idler frequency of 2ωp−ωs suggests four photon parametric interaction. In addition, an anomalous gain saturation effect is experimentally observed whereby the reflected signal power maintains a constant increased value even as the reflected idler power decreases.  
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85.25.Cp Josephson devices
74.25.N- Response to electromagnetic fields
84.40.Dc Microwave circuits
74.72.-h Cuprate superconductors

Elimination of pinholes in epitaxial thin film YBa2Cu3O7−x/SrTiO3/PrGaO3 multilayers

E. Olsson, G. Brorsson, P. Å. Nilsson, and T. Claeson

Appl. Phys. Lett. 63, 1567 (1993); http://dx.doi.org/10.1063/1.110751 (3 pages) | Cited 4 times

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Pinholes have been eliminated in trilayers of YBa2Cu3O7−x(YBCO)/PrGaO3(PGO)/YBCO by introducing 13‐nm‐thick SrTiO3(STO) films in the intermediate PGO film. The STO continuously covers the bottom YBCO layer and promotes a uniform growth of the subsequent PGO films. The individual PGO films are of high quality up to a thickness of about 40 nm where voids start to appear in the films. The voids disrupt the continuity of the subsequent STO and PGO layers. The technique of introducing thin layers that establish the growth of pinhole‐free films can be used for other similar multilayer systems that suffer from pinholes between individual films.
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74.78.Fk Multilayers, superlattices, heterostructures
74.78.-w Superconducting films and low-dimensional structures
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.-a Thin film structure and morphology

Interface study of Nb/ZrOx‐Zr/Nb Josephson junctions

Shin’ichi Morohashi, Yuji Kataoka, Teruo Yagishita, and Shinya Hasuo

Appl. Phys. Lett. 63, 1570 (1993); http://dx.doi.org/10.1063/1.110752 (3 pages) | Cited 2 times

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We studied the interfaces in Nb/ZrOx‐Zr/Nb and Nb/AlOx‐Al/Nb Josephson junctions using secondary ion mass spectrometry. An adsorbed water vapor layer, which has detached from the chamber wall, exists at the interface of the Nb/AlOx‐Al/Nb junctions. This layer does not exist at the interface of the Nb/ZrOx‐Zr/Nb junctions. We also find an argon sputtering gas is absorbed in the ZrOx‐Zr layer as much as in Nb layers, but not at all in the AlOx‐Al layer. The adsorbed water vapor layer acts as a weak barrier for grain boundary diffusion in the Nb/AlOx‐Al/Nb structure. In the Nb/ZrOx‐Zr/Nb structure, we believe the adsorbed water vapor layer was sputter‐etched during the Zr deposition, the high melting point of Zr contributes to the stability of the junction interface.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
68.35.Fx Diffusion; interface formation
68.55.-a Thin film structure and morphology

Columnar defects in YBa2Cu3O7−δ induced by irradiation with high energy heavy ions

R. Wheeler, M. A. Kirk, A. D. Marwick, L. Civale, and F. H. Holtzberg

Appl. Phys. Lett. 63, 1573 (1993); http://dx.doi.org/10.1063/1.110753 (3 pages) | Cited 14 times

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Defect microstructures in three YBa2Cu3O7−δ single crystals irradiated with different high energy heavy ions show dramatically different damage morphologies. For Sn and Au projectiles with total energies of 580 MeV and 1.0 GeV, respectively, highly aligned tracks are observed which extend for many microns in the crystals. However, irradiation with 1.4 GeV Br ions results in the formation of spherical damage regions widely separated along the ion path through the entire crystal. The continuity of damage along the ion path for the different projectiles varies with the magnitude of the electronic energy loss.
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61.80.Jh Ion radiation effects
74.72.-h Cuprate superconductors

a‐axis oriented epitaxial YBa2Cu3O7−y/PrBa2Cu3−xNbxO7−z multistructures

S. Hontsu, N. Mukai, J. Ishii, T. Kawai, and S. Kawai

Appl. Phys. Lett. 63, 1576 (1993); http://dx.doi.org/10.1063/1.110809 (3 pages) | Cited 5 times

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Using the pulsed laser deposition technique, we have successfully prepared a‐axis oriented PrBa2Cu3−xNbxO7−z (PBCNO)(x=0–1.5) films and YBa2Cu3O7−x (YBCO)/PBCNO heterorepitaxial multilayer structures. For the PBCNO films, the resistivity showed semiconducting behavior at all Nb substitution levels investigated. The resistivity increased with increasing Nb content, reaching a value of 104 Ω cm at 100 K for a 300‐Å‐thick film with x=1.0. Using (100)SrTiO3 (STO) as a substrate, the following multilayer structures were successfully formed: (100)PBCNO(x=1.0)/(100)YBCO/(100)PBCO//STO, (001) YBCO/(100)PBCNO(x=1.0)/(100)PBCO//STO, and (100)YBCO/(100)PBCO/(100)PBCNO(x=1.0)/(100)PBCO//STO. The bottom and top YBCO layers in the (100)YBCO/(100)PBCO/(100)PBCNO/(100)PBCO/(100)YBCO//STO structure showed superconducting transition temperatures (zero resistance) of 82 and 83 K, respectively. The interlayer resistivity of the 200‐Å‐thick PBCNO(x=1) interlayer was as high as 105 Ω cm at 30 K.
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74.78.Fk Multilayers, superlattices, heterostructures
74.78.-w Superconducting films and low-dimensional structures
68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition

Granular giant magnetoresistance at low fields in bilayer thin films

K. R. Coffey, T. L. Hylton, M. A. Parker, and J. K. Howard

Appl. Phys. Lett. 63, 1579 (1993); http://dx.doi.org/10.1063/1.110754 (3 pages) | Cited 8 times

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Granular giant magnetoresistance is observed at saturation fields of 350–1100 Oe in thin‐film structures consisting of a discontinuous layer of Co or NiFe deposited on an insulating substrate and overcoated with Cu. The phenomena are similar to that recently observed in codeposited immiscible alloys such as Co‐Cu, although at lower fields. The bilayer structure does not require immiscibility and thus allows a greater materials choice. Magnetoresistance values up to 3% are observed and the reduced saturation fields are attributed to the controlled size and shape of the ferromagnetic islands.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Tt Fine-particle systems; nanocrystalline materials

Magnetic easy axis randomly in‐plane oriented barium hexaferrite thin film media

Xiaoyu Sui and Mark H. Kryder

Appl. Phys. Lett. 63, 1582 (1993); http://dx.doi.org/10.1063/1.110755 (3 pages) | Cited 45 times

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High coercivity, c‐axis randomly in‐plane oriented barium hexaferrite thin films have been successfully fabricated by using conventional rf diode sputtering and post‐deposition annealing. Coercivities as high as 4100 Oe have been achieved. Ms, Sq, S∗, SFD, and SFDr reach the values of about 270 emu/cc, 0.63, 0.90, 0.12, and 0.084, respectively. CoTi doping not only reduces the coercivity, but also reduces the grain size and improves the c‐axis in‐plane orientation. The composition of doped films can be controlled through different diffusion processes. In this way coercivities in a range between several hundred oersteds and 4000 Oe can be easily obtained.
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75.50.Gg Ferrimagnetics
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.60.-d Domain effects, magnetization curves, and hysteresis

A novel hysteresis loop and indirect exchange coupling in Co/Pt/Gd/Pt multilayer films

K. Takanashi, H. Kurokawa, and H. Fujimori

Appl. Phys. Lett. 63, 1585 (1993); http://dx.doi.org/10.1063/1.110756 (3 pages) | Cited 21 times

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We have investigated the magnetization behavior of Co/Pt/Gd/Pt multilayers in order to study the indirect exchange coupling between Co and Gd through Pt. A novel hysteresis loop has been observed for the samples with Pt layer thicknesses larger than 10 Å. This loop is considered to be due to the combined effect of the antiferromagnetic coupling between Co and Gd layers and the large magnetic anisotropy acting on the Co layer magnetization. The magnetization data suggest that the coupling strength oscillates with the Pt layer thickness.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
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