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29 Dec 1997

Volume 71, Issue 26, pp. 3749-3909

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Origin of dislocation-related photoluminescence bands in very thin silicon–germanium layers grown on silicon substrates

Hosun Lee, Suk-Ho Choi, and T.-Y. Seong

Appl. Phys. Lett. 71, 3823 (1997); http://dx.doi.org/10.1063/1.120516 (3 pages) | Cited 4 times

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We measured the photoluminescence spectra of very thin and partially strained Si1−xGex (0.2 ⩽ x ⩽ 0.5) layers grown on silicon substrates with varying degrees of strain relaxation. We observed photoluminescence lines, so-called D lines, which arise from dislocations in the Si1−xGex/Si alloys. Surprisingly, we observed no D lines originating from the Si1−xGex layers. We identify the origin of the D lines as the penetrated dislocations in the Si substrates extending from the SiGe/Si interface with the assistance of transmission electron microscopy. We discuss possible mechanisms of the dominance of luminescence from the dislocations in the Si substrates over those in the SiGe layers. © 1997 American Institute of Physics.
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78.66.Li Other semiconductors
78.55.Hx Other solid inorganic materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.05.Hd Other semiconductors

Growth conditions for complete substitutional carbon incorporation into Si1−yCy layers grown by molecular beam epitaxy

S. Zerlauth, H. Seyringer, C. Penn, and F. Schäffler

Appl. Phys. Lett. 71, 3826 (1997); http://dx.doi.org/10.1063/1.120517 (3 pages) | Cited 25 times

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To study the conditions for substitutional incorporation of carbon into Si layers, we grew pseudomorphic Si1−yCy/Si superlattices with absolute carbon concentrations between 0.3% and 2% and growth temperatures varying between 400 and 650 °C. We employed a novel technique to derive the amount of substitutional carbon, which is based on comparative x-ray rocking analyses of Si1−yCy/Si superlattices grown with constant and step-graded temperature profiles. At growth rates around 1 Å/s, we find complete substitutional incorporation of carbon up to growth temperatures of 550 °C and carbon concentrations of about 1%. At higher growth temperatures and/or higher carbon concentrations, the percentage of substitutional carbon drops significantly, concomitant with a thus far unnoticed morphological transition to island growth. © 1997 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Ion implantation as a tool for controlling the morphology of porous gallium phosphide

I. M. Tiginyanu, C. Schwab, J.-J. Grob, B. Prévot, H. L. Hartnagel, A. Vogt, G. Irmer, and J. Monecke

Appl. Phys. Lett. 71, 3829 (1997); http://dx.doi.org/10.1063/1.120518 (3 pages) | Cited 20 times

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We investigate the morphology of porous layers obtained by electrochemical anodization of (100)-oriented n-type GaP substrates before and after a preliminary 5-MeV Kr+ implantation. Apart from favoring the observation of a surface-related phonon in the frequency gap between the bulk optical phonons, ion implantation appears to be an effective means of controlling the morphology of porous GaP, irrespective of initial substrate material features. © 1997 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
81.05.Rm Porous materials; granular materials
61.80.Jh Ion radiation effects
81.65.-b Surface treatments
68.35.Ja Surface and interface dynamics and vibrations
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
82.45.-h Electrochemistry and electrophoresis

Evidence for atomic H insertion into strained Si–Si bonds in the amorphous hydrogenated silicon subsurface from in situ infrared spectroscopy

A. von Keudell and J. R. Abelson

Appl. Phys. Lett. 71, 3832 (1997); http://dx.doi.org/10.1063/1.120544 (3 pages) | Cited 15 times

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The reaction of atomic hydrogen with a growing amorphous hydrogenated silicon film plays a crucial role in determining the final material properties: hydrogen saturates dangling bonds in the film and thereby lowers the defect density, and it is assumed that hydrogen is inserted into strained bonds of the silicon network thereby reducing the local disorder. The latter reaction can be inferred indirectly since the total hydrogen uptake exceeds the decrease in the defect density. This letter presents the first direct experimental evidence from in situ infrared spectroscopy for the insertion of hydrogen into strained Si–Si bonds. This reaction becomes visible during the addition of atomic hydrogen to an as-grown film by the appearance of a characteristic SiH vibrational mode at 2033 cm−1, indicating a different embedding Si matrix compared to the standard SiH bulk vibration at 2000 cm−1. © 1997 American Institute of Physics.
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78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Jg Amorphous semiconductors; glasses
71.55.Jv Disordered structures; amorphous and glassy solids
63.50.-x Vibrational states in disordered systems

Ge concentration in regrown GaAs for ohmic contacts

T. J. Kim, P. H. Holloway, and E. A. Kenik

Appl. Phys. Lett. 71, 3835 (1997); http://dx.doi.org/10.1063/1.120519 (3 pages) | Cited 5 times

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Dissociation and solid phase epitaxial regrowth of GaAs in Ti/Ge/Ni/GaAs were investigated using the transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS) of x-rays with spatial resolution approaching 2 nm. A ternary Ni2.4GaAs phase, ∼ 130 nm thick, was formed by 300 °C in situ anneals of 65 nm Ni film on GaAs. After this in situ anneal, films of 30 nm Ge and 20 nm Ti were deposited in sequence. The EDS analysis showed that Ni2.4GaAs transformed into Ni–As and Ni–Ga binaries after annealing at 500 °C for 5 min, while ∼ 30 nm of GaAs regrew by solid phase epitaxial regrowth from decomposition of the binary phases. High spatial resolution microanalysis allowed detection of ∼ 1×1020 cm−3 Ge in the regrown GaAs. This confirms that Ge is incorporated into GaAs during regrowth for ohmic contact formation. © 1997 American Institute of Physics.
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81.15.Np Solid phase epitaxy; growth from solid phases
68.55.Nq Composition and phase identification
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
61.72.Cc Kinetics of defect formation and annealing

A silicon Coulomb blockade device with voltage gain

R. A. Smith and H. Ahmed

Appl. Phys. Lett. 71, 3838 (1997); http://dx.doi.org/10.1063/1.120543 (3 pages) | Cited 25 times

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A silicon single electron tunneling transistor (SETT), which shows an inverting voltage gain greater than unity and as high as 3.7, has been fabricated. The blockade voltage as a function of gate voltage shows sawtooth oscillations when biased with a small current and measured at a temperature of 4.2 K. The SETT is fabricated in highly doped and oxidized silicon quantum wires of less than a 40 nm×50 nm cross section and 1.5 μm length. © 1997 American Institute of Physics.
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85.35.Gv Single electron devices
85.35.Ds Quantum interference devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.61.Cw Elemental semiconductors

Spatially resolved luminescence studies of defects and stress in aluminum gallium nitride films

L. H. Robins and D. K. Wickenden

Appl. Phys. Lett. 71, 3841 (1997); http://dx.doi.org/10.1063/1.120520 (3 pages) | Cited 7 times

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Aluminum gallium nitride (AlxGa1−xN) films with x = 0 to x = 0.36, grown by metal–organic chemical vapor deposition on sapphire, were characterized by cathodoluminescence (CL) imaging and spectroscopy, photoluminescence (PL) spectroscopy, and optical microscopy. In each film, the CL and PL spectra excited from the top surface show a narrow band-edge peak and a broad deep-level peak. In some films, the PL spectrum excited from the film–substrate interface (through the sapphire substrate) shows an additional narrow peak below the band edge, which is attributed to interfacial defects. CL imaging and optical microscopy reveal two types of large-scale defects: networks of lines, which are probably microcracks, and roughly hexagonal raised areas. The hexagonal areas occur only in the lower-x films, while the microcrack density increases with x. Spatially resolved CL spectra taken near the large-scale defects show large peak shifts attributed to stress relaxation, and below band-edge peaks attributed to localized states. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.60.Bs Mechanical and acoustical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.60.Hk Cathodoluminescence, ionoluminescence
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
71.55.Eq III-V semiconductors

H-complexed oxygen vacancy in SiO2: Energy level of a negatively charged state

V. V. Afanas’ev and A. Stesmans

Appl. Phys. Lett. 71, 3844 (1997); http://dx.doi.org/10.1063/1.120521 (3 pages) | Cited 11 times

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The defects generated in SiO2 during irradiation with energetic (10 eV) photons were found to trap electrons at a level 3.1 eV below the oxide conduction band. The electron spin resonance data and the behavior upon hydrogen passivation indicate that the optically active state may be ascribed to a H-complexed oxygen vacancy in SiO2. The observed injection of electrons to these traps from Si advances the revealed defects as the possible origin of the degradation-induced electrical conduction of thin SiO2 layers. © 1997 American Institute of Physics.
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61.72.Yx Interaction between different crystal defects; gettering effect
71.55.Ht Other nonmetals
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
76.30.-v Electron paramagnetic resonance and relaxation

High performance ZnSTe photovoltaic visible-blind ultraviolet detectors

I. K. Sou, C. L. Man, Z. H. Ma, Z. Yang, and G. K. L. Wong

Appl. Phys. Lett. 71, 3847 (1997); http://dx.doi.org/10.1063/1.120522 (3 pages) | Cited 10 times

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ZnS1−xTex-based Schottky photodiodes have been fabricated on various substrates using the molecular beam epitaxy technique. The photovoltage output of these photovoltaic devices is determined using Fourier transform interferometric spectroscopy. The results show that these devices (with Te<10%) are highly sensitive in the ultraviolet but are visible blind. An external quantum efficiency of over 50% has been achieved on a device grown on a GaP substrate and over 40% on a Si substrate. © 1997 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Pw Imaging detectors and sensors
85.60.Dw Photodiodes; phototransistors; photoresistors
78.66.Hf II-VI semiconductors

Positron irradiation: A technique for modifying the photoluminescent structures of porous silicon

Y. M. Huang

Appl. Phys. Lett. 71, 3850 (1997); http://dx.doi.org/10.1063/1.120523 (3 pages) | Cited 4 times

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It has been shown that a two-peak green photoluminescence (PL) of porous silicon (PS) can be obtained from a continuous blueshift of a red PL by positron irradiation. At room temperature, PS samples were irradiated in air by energetic positrons coming from the conventionally used isotope 22Na ( ∼ 20 μCi). With increasing positron irradiation time, an originally red PL shifted continuously to green, then a two-peak PL appeared with a weak high-energy emission band (529 nm) and a low-energy dominant band (562 nm). The intensity of this high-energy band was enhanced by prolonged positron irradiation. The electron-spin-resonance signal combined with infrared absorption showed that positron irradiation created dangling bonds and stimulated oxide growth in PS. An interpretation is given on the basis of quantum confinement and atomiclike nature for very small nano-Si crystallites. © 1997 American Institute of Physics.
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61.82.Fk Semiconductors
61.80.Fe Electron and positron radiation effects
78.55.Ap Elemental semiconductors
81.05.Rm Porous materials; granular materials
81.05.Cy Elemental semiconductors
76.30.Mi Color centers and other defects
78.30.Am Elemental semiconductors and insulators

Oligophenyl-based organic thin film transistors

D. J. Gundlach, Y.-Y. Lin, T. N. Jackson, and D. G. Schlom

Appl. Phys. Lett. 71, 3853 (1997); http://dx.doi.org/10.1063/1.120524 (3 pages) | Cited 51 times

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Organic thin film transistors (TFTs) have been fabricated using thermally evaporated films of the oligophenyls p-quaterphenyl (p-4P), p-quinquephenyl (p-5P), and p-sexiphenyl (p-6P). The field-effect mobility of these TFTs ranges from 10−2 cm2/V s for p-4P to 10−1 cm2/V s for p-6P with on/off current ratio from 105 to 106. These values are comparable to those achieved using the more widely studied organic semiconductors alpha-sexithienyl (α-6T) and pentacene. X-ray diffraction reveals a high degree of molecular ordering, believed to be important for obtaining high field-effect mobility in organic TFTs. © 1997 American Institute of Physics.
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85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds

Phonons as probes in self-organized SiGe islands

J. Groenen, R. Carles, S. Christiansen, M. Albrecht, W. Dorsch, H. P. Strunk, H. Wawra, and G. Wagner

Appl. Phys. Lett. 71, 3856 (1997); http://dx.doi.org/10.1063/1.120525 (3 pages) | Cited 57 times

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We show how optical phonons can be used as efficient probes in self-organized Si1−xGex islands grown on Si(001). Both the alloy composition and residual strain in the islands were originally determined from the phonon frequencies and Raman intensities. The experimental results are in good agreement with the strain relaxation simulated by means of the finite element method. © 1997 American Institute of Physics.
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68.35.Ja Surface and interface dynamics and vibrations
68.60.Bs Mechanical and acoustical properties
78.30.Hv Other nonmetallic inorganics
78.66.Li Other semiconductors
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
02.70.Dh Finite-element and Galerkin methods
63.20.-e Phonons in crystal lattices
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Analysis of a thin AlN interfacial layer in Ti/Al and Pd/Al ohmic contacts to n-type GaN

B. P. Luther, J. M. DeLucca, S. E. Mohney, and R. F. Karlicek

Appl. Phys. Lett. 71, 3859 (1997); http://dx.doi.org/10.1063/1.120526 (3 pages) | Cited 50 times

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Using high resolution transmission electron microscopy, a thin pseudomorphic AlN layer (2–3 nm) has been observed at the metal/GaN interfaces of Ti/Al (35/115 nm) and Pd/Al (25/125 nm) ohmic contacts to n-type GaN annealed in Ar at 600 °C for 15 and 30 s, respectively. The interfacial layer has a c-plane (002) lattice spacing of 2.48±.03 Å and an a-plane (100) spacing matching that of GaN (2.76 Å), and the identification of this layer as AlN is consistent with chemical analysis by energy dispersive x-ray spectroscopy. The formation of this interfacial AlN layer coincides with the onset of ohmic behavior in Ti/Al and Pd/Al contacts annealed at 600 °C and may be the cause. © 1997 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
68.35.Ct Interface structure and roughness
61.72.Cc Kinetics of defect formation and annealing
79.60.Jv Interfaces; heterostructures; nanostructures

The interstitial fraction of diffusivity of common dopants in Si

H.-J. Gossmann, T. E. Haynes, P. A. Stolk, D. C. Jacobson, G. H. Gilmer, J. M. Poate, H. S. Luftman, T. K. Mogi, and M. O. Thompson

Appl. Phys. Lett. 71, 3862 (1997); http://dx.doi.org/10.1063/1.120527 (3 pages) | Cited 44 times

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The relative contributions of interstitials and vacancies to diffusion of a dopant A in silicon are specified by the interstitial fraction of diffusivity, fA. Accurate knowledge of fA is required for predictive simulations of Si processing during which the point defect population is perturbed, such as transient enhanced diffusion. While experimental determination of fA is traditionally based on an underdetermined system of equations, we show here that it is actually possible to derive expressions that give meaningful bounds on fA without any further assumptions but that of local equilibrium. By employing a pair of dopants under the same point-defect perturbance, and by utilizing perturbances very far from equilibrium, we obtain experimentally fSb ⩽ 0.012 and fB ≥ 0.98 at temperatures of ∼ 800 °C, which are the strictest bounds reported to date. Our results are in agreement with a theoretical expectation that a substitutional dopant in Si should either be a pure vacancy, or a pure interstitial(cy) diffuser. © 1997 American Institute of Physics.
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66.30.J- Diffusion of impurities
61.72.J- Point defects and defect clusters
66.30.Dn Theory of diffusion and ionic conduction in solids

Recombination characteristics of minority carriers near the AlxOy/GaAs interface using the light beam induced current technique

H. Gebretsadik, K. Zhang, K. Kamath, X. Zhang, and P. Bhattacharya

Appl. Phys. Lett. 71, 3865 (1997); http://dx.doi.org/10.1063/1.120545 (3 pages) | Cited 5 times

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The light beam induced current (LBIC) technique was used to characterize the interface formed by the wet oxidation of AlAs and AlxGa1−xAs (x = 0.98 and 0.95). LBIC scans were used to calculate the diffusion lengths of minority carriers both in the bulk and near these interfaces; and the corresponding interface recombination velocities were estimated. The interface recombination velocity at the oxide/semiconductor interface is 3.13×105 cm/s for AlAs, and 1.90×104 cm/s for Al0.98Ga0.02As. It is found that the addition of gallium in the AlAs can significantly improve this property. © 1997 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.25.+i Surface conductivity and carrier phenomena
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.65.Mq Oxidation
72.40.+w Photoconduction and photovoltaic effects

Composition evaluation of InxGa1−xAs Stranski-Krastanow-island structures by strain state analysis

A. Rosenauer, U. Fischer, D. Gerthsen, and A. Förster

Appl. Phys. Lett. 71, 3868 (1997); http://dx.doi.org/10.1063/1.120528 (3 pages) | Cited 40 times

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The compositional analyses of InxGa1−x/GaAs (001) island structures grown by molecular beam epitaxy at a substrate temperature of 560 °C with nominal In contents of x = 60% and 100% are presented on the basis of high resolution transmission electron microscopy micrographs. The linear dependence of the lattice parameter on the In content (Vegard’s law) is exploited to quantitatively derive composition profiles on an atomic scale by measuring local lattice parameters and displacements. The relaxation of the thin transmission electron microscopy specimen is taken into account by the accurate thickness determination using the quantitative analysis of the information from transmission electron micrographs procedure. The final evaluation step consists of finite element modeling with the appropriate sample geometry, where the In distribution is chosen to obtain the best fit between experimental and simulated displacements. The observed In content is significantly smaller than the nominal In concentration which is due to segregation of In and diffusion of Ga from the GaAs buffer into the island during the growth. The measured mean In concentration of the islands with a nominal In content of 60% (100%) is 24% (45%). © 1997 American Institute of Physics.
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68.55.Nq Composition and phase identification
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
02.70.Dh Finite-element and Galerkin methods
64.75.-g Phase equilibria
81.05.Ea III-V semiconductors

Bis(dithienothiophene) organic field-effect transistors with a high ON/OFF ratio

H. Sirringhaus, R. H. Friend, X. C. Li, S. C. Moratti, A. B. Holmes, and N. Feeder

Appl. Phys. Lett. 71, 3871 (1997); http://dx.doi.org/10.1063/1.120529 (3 pages) | Cited 40 times

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A conjugated, fused-thiophene oligomer, bis(dithienothiophene) (BDT), has been synthesized and deposited by vacuum sublimation as the active layer in organic thin film transistors (TFTs). The TFTs show exceptionally high ON/OFF ratios up to 108 between accumulation and depletion with sharp turn-on characteristics comparable to that of amorphous silicon TFTs (subthreshold slope S=0.6 V/decade). Field-effect mobilities are 0.02–0.05 cm2/V s. The good performance is explained by the relatively high π-π∗ gap of the short-chain BDT molecule and the favorable coplanar π-π stacking in BDT, differing from the herringbone stacking in the oligothiophenes. © 1997 American Institute of Physics.
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85.30.Tv Field effect devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.05.Hd Other semiconductors

Identification of isolation-edge related random telegraph signals in submicron silicon metal–oxide–semiconductor field-effect transistors

N. Lukyanchikova, M. V. Petrichuk, N. Garbar, E. Simoen, and C. Claeys

Appl. Phys. Lett. 71, 3874 (1997); http://dx.doi.org/10.1063/1.120530 (3 pages) | Cited 2 times

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In this letter, evidence is given for a new class of random telegraph signals (RTSs) in submicron n-metal–oxide–semiconductor field-effect transistors (n-MOSFETs). These two-level fluctuations not only occur when the MOSFET is biased in linear operation but also when it is operated in the source or drain-substrate diode mode. A detailed investigation of the RTS parameters, i.e., the amplitude, the emission, and the capture time constants, reveal a close correlation with the current through the forward biased drain- (or source-) substrate diode. At the same time, from the substrate bias dependence of the trap characteristics, it is inferred that it behaves like a near-interface oxide trap. From this, it is concluded that the most likely position is along the channel width perimeter, at the isolation edges of the transistors and close to the source or drain junction. © 1997 American Institute of Physics.
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85.30.Tv Field effect devices
72.70.+m Noise processes and phenomena

Electron multiplication in AlxGa1−xAs/GaAs heterostructures

C. K. Chia, J. P. R. David, G. J. Rees, P. N. Robson, S. A. Plimmer, and R. Grey

Appl. Phys. Lett. 71, 3877 (1997); http://dx.doi.org/10.1063/1.120531 (3 pages) | Cited 9 times

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We have measured the electron multiplication characteristics of thin ( ∼ 0.1 μm) AlxGa1−xAs(500 Å)/GaAs(500 Å) single heterostructures with 0.3 ⩽ x ⩽ 0.6, grown in a p-i-n configuration. In these devices, at low electric fields, the electron multiplication occurs mainly in the latter half of the i region because of dead space effects. As the electric field increases the multiplication behavior converges to that of the equivalent alloy. Our measurements show that the electron multiplication in these structures never exceeds that of GaAs. A simple Monte Carlo simulation suggests that the advantage obtained from the conduction band edge step down from AlxGa1−xAs to GaAs is offset by the energy loss via higher phonon emission in the AlxGa1−xAs layer. © 1997 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Fq High-field and nonlinear effects
02.70.Rr General statistical methods
02.50.Ng Distribution theory and Monte Carlo studies
85.30.De Semiconductor-device characterization, design, and modeling
77.22.Jp Dielectric breakdown and space-charge effects

Photoluminescence properties of GaN grown on compliant silicon-on-insulator substrates

J. Cao, D. Pavlidis, A. Eisenbach, A. Philippe, C. Bru-Chevallier, and G. Guillot

Appl. Phys. Lett. 71, 3880 (1997); http://dx.doi.org/10.1063/1.120532 (3 pages) | Cited 22 times

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A compliant substrate approach has been employed to release lattice-mismatch caused strain in GaN epilayers through stress absorption in the substrate. GaN layers have been grown on silicon-on-insulator (SOI) substrates by low-pressure metalorganic chemical vapor deposition. Photoluminescence measurements at 4 K show the spectrum of grown GaN being dominated by UV emission around 3.47 eV related to neutral-donor bound excitons. The much weaker yellow luminescence shows a broad spectrum around 2.16 eV. Peak position of the UV emission changes both with measurement temperature and strain. At room temperature, the UV peak is red shifted by 64 meV corresponding well to the band-gap temperature dependence. Strain-induced blue shift of the peak, compared to unstrained GaN, is much less than for growth on sapphire, indicating strain relief in the GaN by growth on SOI. Further reduction of the blue shift is consistent with increased electron mobility. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
71.35.-y Excitons and related phenomena
62.20.-x Mechanical properties of solids

Characteristics of GaAs and AlGaAs homojunction avalanche photodiodes with thin multiplication regions

K. A. Anselm, P. Yuan, C. Hu, C. Lenox, H. Nie, G. Kinsey, J. C. Campbell, and B. G. Streetman

Appl. Phys. Lett. 71, 3883 (1997); http://dx.doi.org/10.1063/1.120533 (3 pages) | Cited 10 times

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The gain and noise of thin GaAs and Al0.2Ga0.8As homojunction avalanche photodiodes were measured. The gain and the excess noise factor were found to be significantly lower than would be expected using ionization coefficients reported in the literature. The discrepancy is believed to be due to physical effects that become significant in thin multiplication layers. It is shown that the gain and excess noise under electron injection can be accurately fit using conventional models with width-dependent ionization coefficients. © 1997 American Institute of Physics.  
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85.60.Dw Photodiodes; phototransistors; photoresistors

Stability of CdSe and ZnSe dots self-organized on semiconductor surfaces

I. Suemune, T. Tawara, T. Saitoh, and K. Uesugi

Appl. Phys. Lett. 71, 3886 (1997); http://dx.doi.org/10.1063/1.120534 (3 pages) | Cited 16 times

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Several monolayers (ML) of CdSe were deposited on (001) GaAs surfaces to study the stability of the CdSe films. The CdSe film with the 2 ML thickness showed atomically flat surfaces just after the growth. However, in three days after the growth, self-organization into dots at room temperature was clearly observed. This unexpected self-organization of dots observed at room temperature from the once coherently-grown CdSe film will be closely correlated to the enhancement of the heterointerface diffusion observed in this combination of CdSe and GaAs. This correlation between the stability of the dots and the heterointerface diffusion was examined in the common cation case of ZnSe/ZnS, which is known to show low interface diffusion. Self-organization of ZnSe dots was observed with an atomic force microscope on (001) ZnS surfaces. The ZnSe dots were stable as expected and did not show instability such as observed for the CdSe dots on GaAs or on ZnSe. © 1997 American Institute of Physics.
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81.05.Dz II-VI semiconductors
68.35.Fx Diffusion; interface formation
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
68.35.B- Structure of clean surfaces (and surface reconstruction)

Temperature dependence of Fermi level obtained by electroreflectance spectroscopy of undoped n+-type doped GaAs

K. M. Huang, K. L. Wang, D. P. Wang, K. F. Huang, T. C. Huang, and A. K. Chu

Appl. Phys. Lett. 71, 3889 (1997); http://dx.doi.org/10.1063/1.120535 (3 pages)

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The electroreflectance (ER) spectra of an undoped n+-type doped GaAs have been measured over a range of temperature from 25 to 400 K. Many Franz–Keldysh oscillations were observed above the band-gap energy, which enabled the electric field strength and, hence, also the Fermi level to be determined. The photovoltaic effect is shown to be negligible, even at the low temperature. The experiment shows that the Fermi level decreases with increasing temperature and has almost the same temperature dependence as the energy gap. It is pinned at about 0.63 of energy gap below the conduction band. © 1997 American Institute of Physics.  
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78.20.Jq Electro-optical effects
71.20.Nr Semiconductor compounds

Determination of irreversibility field variations in mono- and multifilamentary (Bi,Pb)2Sr2Ca2Cu3Ox tapes by transport current methods

J. W. Anderson, J. A. Parrell, M. Polak, and D. C. Larbalestier

Appl. Phys. Lett. 71, 3892 (1997); http://dx.doi.org/10.1063/1.120546 (3 pages) | Cited 8 times

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The irreversibility field, H∗, has been measured for a variety of mono- and multifilamentary (Bi,Pb)2Sr2Ca2Cu3Ox (2223) tapes using two different transport current techniques. It is common to characterize the quality of 2223 tapes by their zero-field, 77 K critical current density [Jc(0 T, 77 K)], even though this ignores the fact that significant self-fields depress Jc(0 T, 77 K) and the possibility that the in-field Jc(B) characteristics may be optimized independently of the Jc(0 T, 77 K) value. To provide more useful information, we propose a second characterization, that of the irreversibility field, H∗. Having both H∗ and Jc(0 T, 77 K) information helps in separating the two independent contributions that better connectivity and stronger flux pinning can make to the Jc of a tape. We illustrate this point with results from a variety of mono- and multifilamentary Bi-2223/Ag tapes in damaged and undamaged conditions, which show that H∗ (77 K) can vary from ∼ 100 to ∼ 200 mT and not directly correlate with Jc(0 T, 77 K). The two proposed protocols for H∗ measurement are robust and compatible with common transport measurement procedures. © 1997 American Institute of Physics.
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74.25.Sv Critical currents
84.71.Mn Superconducting wires, fibers, and tapes
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.72.-h Cuprate superconductors

Origin of peak effect in the magnetization hysteresis loop of melt-processed REBa2Cu3Oy superconductors

N. V. N. Viswanath, T. Rajasekharan, Latika Menon, N. Harish Kumar, S. K. Malik, G. K. Dey, and D. D. Upadhyaya

Appl. Phys. Lett. 71, 3895 (1997); http://dx.doi.org/10.1063/1.120536 (3 pages) | Cited 4 times

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Melt-processed Sm-123 samples with an excess Sm2BaCuOy (Sm-211) phase is studied by transmission electron microscope (TEM) and superconducting quantum interference device magnetometer, to explain the origin of the peak effect exhibited in the magnetization hysteresis loops of light RE-123 samples in intermediate fields at 77 K. TEM images of the sample showing peak effect reveal dilute concentrations of areas with ortho-II structure distributed on a nanometer scale within the twin regions of the sample. The ortho-II structure is an oxygen deficient 123 with a lower Tc than the bulk of the material and will be a source of flux pinning by turning normal in high fields, thus contributing to the peak effect. With an increase in Sm-211 concentration, the peak effect disappears from the hysteresis loop, as does the ortho-II structure in the TEM images. © 1997 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Ha Magnetic properties including vortex structures and related phenomena
64.75.-g Phase equilibria
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