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27 Jan 1997

Volume 70, Issue 4, pp. 405-531

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A phase-locked shear-force microscope for distance regulation in near-field optical microscopy

Walid A. Atia and Christopher C. Davis

Appl. Phys. Lett. 70, 405 (1997); http://dx.doi.org/10.1063/1.118318 (3 pages) | Cited 41 times

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A nonoptical phase-locked shear-force microscope utilizing a quartz crystal tuning fork acting as a voltage-controlled oscillator in a phase-locked loop has been implemented. A tapered optical fiber is rigidly mounted on one of the prongs of the fork to serve as both a shear-force pickup and a near-field optical probe. The crystal is driven at its resonance frequency through positive feedback of the monitored current through the crystal. This signal is used as the voltage-controlled oscillator in a phase-locked loop. The scheme allows for scan speeds far beyond the Q-limited amplitude sensor bandwidth and exhibits excellent sensitivity for a high-Q resonator. Furthermore, given the small vibration amplitude of the tip (<0.5 nm) and the distance over which it is reduced (> 6 nm), it is unlikely that the tip is making direct contact with the sample surface as has been suggested for the optical shear-force detection scheme. © 1997 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
77.65.Fs Electromechanical resonance; quartz resonators
43.38.Fx Piezoelectric and ferroelectric transducers

Cathodoluminescence study of GaAs quantum wells and of submicron dots fabricated by magnetron reactive ion etching

L.-L. Chao, G. S. Cargill, M. Levy, R. M. Osgood, and G. F. McLane

Appl. Phys. Lett. 70, 408 (1997); http://dx.doi.org/10.1063/1.119124 (3 pages) | Cited 6 times

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Cathodoluminescence has been employed to investigate the luminescence and lateral transport properties of excited carriers at 8 K in GaAs-AlGaAs quantum well material and in submicron features fabricated in this material by magnetron reactive ion etching. A carrier diffusion length of 0.85±0.04 μm in quantum wells and a surface recombination velocity (5.4±0.8)×103 m/s at etched sidewalls were measured. Also, the effect of feature size on luminescence efficiency was examined and compared with model calculations using the measured values of diffusion length and surface recombination velocity. © 1997 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
73.61.Ey III-V semiconductors
81.15.Cd Deposition by sputtering

Quantum-well activated phosphors: A new concept for electroluminescent displays

R. Engelmann, J. Ferguson, and R. Solanki

Appl. Phys. Lett. 70, 411 (1997); http://dx.doi.org/10.1063/1.118319 (3 pages) | Cited 6 times

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The development of a completely new class of artificially engineered phosphors for electroluminescent displays is proposed in which deep quantum wells embedded in a high band gap material act as radiative centers. The proof of concept of such phosphor activation by quantum wells (QWs) has been demonstrated in the CdSe/SrS multi-quantum well system prepared by atomic layer epitaxy. Various QW widths (3–15 nm) were studied. The reduction in QW width shifts the emission towards shorter wavelength and the emission spectra exhibit multiple peaks, believed to be the result of transitions from several QW levels. © 1997 American Institute of Physics.
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85.60.Pg Display systems
78.60.Fi Electroluminescence
42.79.Kr Display devices, liquid-crystal devices

Photoconductivity nonlinearity at high excitation power in quantum well infrared photodetectors

M. Ershov, H. C. Liu, M. Buchanan, Z. R. Wasilewski, and V. Ryzhii

Appl. Phys. Lett. 70, 414 (1997); http://dx.doi.org/10.1063/1.118320 (3 pages) | Cited 32 times

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Nonlinear photoconductivity effects at high excitation power in quantum well infrared photodetectors (QWIPs) are studied both experimentally and theoretically. The photoconductivity nonlinearity is mainly caused by a redistribution of the electric potential at high power, which leads to a decrease of electric field in the bulk of the QWIP. As a result of the decreased field, the photoexcited electron escape probability and drift velocity decrease resulting in a decrease of responsivity. © 1997 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.50.Pz Photoconduction and photovoltaic effects
73.50.Fq High-field and nonlinear effects

Atomic force microscope study of photo-polymerized and photo-dimerized epitaxial C60 films

A. Hassanien, J. Gasperič, J. Demsar, I. Muševič, and D. Mihailovic

Appl. Phys. Lett. 70, 417 (1997); http://dx.doi.org/10.1063/1.118321 (3 pages) | Cited 9 times

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We have used an atomic force microscope to analyze the surface of C60 thin films, which have been grown epitaxially on a mica surface and illuminated with a 514.5 nm laser light at different temperatures. Two regimes of light-induced polymerization are observed. If the illumination temperature Tp is lower than 320 K, the illuminated surface shows polymer chains typically six molecules long with an intermolecular distance of 9.2±0.1 Å . Because of the strain associated with the shorter inter-C60 distance in the polymer compared to the bulk, the surface is buckled with a period of ∼ 100 Å and amplitude of ∼5 Å resulting in a characteristic herringbone three-dimensional structure. For films, illuminated above 350 K, the surface shows primarily dimers and trimers with an unusually short inter-C60 distance of 8.8±0.1 Å, this being the shortest interbuckyball distance reported so far. We also find large changes in the adhesive forces on the polymerized films compared to unpolymerized ones, suggesting that the polymer is substantially more hydrophyllic than normal C60. © 1997 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)

Correlation of cathodoluminescence inhomogeneity with microstructural defects in epitaxial GaN grown by metalorganic chemical-vapor deposition

S. J. Rosner, E. C. Carr, M. J. Ludowise, G. Girolami, and H. I. Erikson

Appl. Phys. Lett. 70, 420 (1997); http://dx.doi.org/10.1063/1.118322 (3 pages) | Cited 248 times

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We discuss the relationship between microstructure and luminescence efficiency for heteroepitaxial films of GaN grown on c-axis sapphire substrates by metalorganic chemical-vapor deposition. We directly characterize the correlation between threading dislocations as observed by transmission electron microscopy, surface morphology as observed by atomic force microscopy, and wavelength-resolved cathodoluminescence imaging. We show that the inhomogeneity in the luminescence intensity of these films near band edge can be accounted for by a simple model where nonradiative recombination at threading dislocations causes a deficiency of minority carriers and results in dark regions of the epilayer. An upper bound for average diffusion length is estimated to be 250 nm. © 1997 American Institute of Physics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.60.Hk Cathodoluminescence, ionoluminescence
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Densities of Si determined by an image digitizing technique in combination with an electrostatic levitator

K. Ohsaka, S. K. Chung, W. K. Rhim, and J. C. Holzer

Appl. Phys. Lett. 70, 423 (1997); http://dx.doi.org/10.1063/1.118317 (3 pages) | Cited 17 times

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We have determined the densities of Si in the liquid, ρl(T), and solid, ρs(T), states as a function of temperature, T, by employing an image digitizing technique and numerical calculation methods in combination with an electrostatic levitator. The obtained density data can be fitted with the following equations: ρl(T) = ρl(Tm)−1.71×10−4(T−Tm)−1.61×10−7(T−Tm)2(g/cm3); ρs(T) = ρs(Tm)−2.63×10−5(T−Tm)(g/cm3),where Tm is the melting point, 1687 K, and ρl(Tm) and ρs(Tm) are 2.580 and 2.311 (g/cm3), respectively. The error involved in the determination is estimated to be ±0.006 (g/cm3). The ρl(T) value smoothly varies through Tm and does not indicate a reported anomalous density variation. The ρl(Tm) value is 2% larger than the literature value and the coefficient of the linear temperature dependence is approximately half of a reported value. The ρs(Tm) value closely agrees with the literature value. © 1997 American Institute of Physics.
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65.40.De Thermal expansion; thermomechanical effects
64.70.K- Solid-solid transitions
81.05.Cy Elemental semiconductors

Temperature dependent segregation of metals at Si–SiO2 interfaces during oxygen ion bombardment

J. S. Williams, K. T. Short, and A. E. White

Appl. Phys. Lett. 70, 426 (1997); http://dx.doi.org/10.1063/1.118170 (3 pages) | Cited 6 times

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Rutherford backscattering and channeling techniques have been used to study temperature-dependent segregation of Cu, Au, and Pd at Si–SiO2 interfaces during high dose 15 keV O+ bombardment of Si. Results illustrate a strong tendency for metals to be retained in an amorphous Si layer adjacent to the continuous SiO2 layer formed by O+ bombardment of Si. The magnitude of segregation depends on the bombardment temperature. We explain our temperature-dependent data in terms of a thermodynamic model whereby the segregation is driven by a large solubility difference between metals in amorphous Si and SiO2. Segregation is enhanced when the metal diffusivity in amorphous Si is high. © 1997 American Institute of Physics.
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61.80.Jh Ion radiation effects
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
61.72.Dd Experimental determination of defects by diffraction and scattering

Three dimensional polarization dependence of OH bands absorption in potassium niobate crystals

Xiaolin Tong, Amnon Yariv, Min Zhang, and Aharon Agranat

Appl. Phys. Lett. 70, 429 (1997); http://dx.doi.org/10.1063/1.118171 (3 pages) | Cited 1 time

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Absorption band countered on wave numbers 3504 and 6843 cm−1 have been observed in potassium niobate crystals. These absorption bands correspond to the transition energies of O–H stretching vibration, from the ground state to the first excited state and to the second excited state, respectively. Absorption bands around 3992 and 4476 cm−1 are attributed to the combination of O–H vibration plus libration. The integrated absorption intensities around 3504, 3992, and 4476 cm−1 are three dimensional polarization dependent which indicates the motion properties of hydrogen ions in the lattice. © 1997 American Institute of Physics.
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78.30.Hv Other nonmetallic inorganics
63.20.Pw Localized modes
66.30.Lw Diffusion of other defects
42.70.Mp Nonlinear optical crystals

The ring-hexavacany in silicon: A stable and inactive defect

S. K. Estreicher, J. L. Hastings, and P. A. Fedders

Appl. Phys. Lett. 70, 432 (1997); http://dx.doi.org/10.1063/1.118172 (3 pages) | Cited 41 times

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Molecular dynamics simulations as well as ab initio and near ab initio Hartree-Fock calculations in crystalline silicon predict that the configuration of the hexavacancy that has a hexagonal ring missing from the crystal is remarkably stable. The energetics imply that it does form and is more likely to grow than to dissociate during heat treatments. Further, the energy eigenvalues and the charge distribution imply that it has no electrical or optical activity. However, it is a large void in the crystal and could be an efficient gettering center and a precursor of extended defects. © 1997 American Institute of Physics.
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61.72.J- Point defects and defect clusters
61.72.Bb Theories and models of crystal defects
71.55.Cn Elemental semiconductors

Fabrication of small diamond tips for scanning probe microscopy application

E. Oesterschulze, W. Scholz, Ch. Mihalcea, D. Albert, B. Sobisch, and W. Kulisch

Appl. Phys. Lett. 70, 435 (1997); http://dx.doi.org/10.1063/1.118173 (3 pages) | Cited 20 times

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A process for the fabrication of diamond cantilevers integrated on a silicon wafer is presented. At one end the cantilevers possess a tip with a small radius of curvature thus allowing their use in scanning probe microscopy applications. The influence of various procedures to enhance diamond nucleation of the properties of the tips is investigated. Ultrasonic pretreatment with 1 μm diamond paste and subsequent hot-filament chemical-vapor deposition turned out to yield the best results. Micro-Raman measurements show the tips to consist of stress-free diamond up to their very apex. © 1997 American Institute of Physics.
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07.79.Cz Scanning tunneling microscopes
81.05.ub Fullerenes and related materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Depth-resolved and excitation power dependent cathodoluminescence study of GaN films grown by metalorganic chemical vapor deposition

X. Li and J. J. Coleman

Appl. Phys. Lett. 70, 438 (1997); http://dx.doi.org/10.1063/1.118174 (3 pages) | Cited 26 times

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We have studied the luminescence properties of GaN films grown by metalorganic chemical vapor deposition using depth-resolved and excitation power dependent cathodoluminescence spectroscopy. In the thickness range we studied ( ∼ 3 μm), the luminescence properties, measured by the ratio of band-edge emission to the yellow band intensity, improve as the layer thickness increases. © 1997 American Institute of Physics.
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71.55.Eq III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Enhancement of Schottky barrier height in heterodimensional metal-semiconductor contacts

T. Ytterdal, M. S. Shur, M. Hurt, and W. C. B. Peatman

Appl. Phys. Lett. 70, 441 (1997); http://dx.doi.org/10.1063/1.118175 (2 pages) | Cited 11 times

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We report on the measurements of the heterodimensional Schottky barrier height in two-dimensional metal-semiconductor field effect transistors (2D MESFETs). Our experimental data indicate approximately 0.1 eV greater barrier height compared to conventional metal-semiconductor contacts of the same materials. The enhancement is explained in terms of two effects—quantization of energy levels of the carriers in the quantum well and broadening of the corresponding wave functions. The increased barrier height leads to a substantial reduction of the gate leakage current in 2D MESFETs. © 1997 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Tv Field effect devices
73.40.Ns Metal-nonmetal contacts

Compressively strained multiple quantum well InAsSb lasers emitting at 3.6 μm grown by metal-organic chemical vapor deposition

B. Lane, D. Wu, A. Rybaltowski, H. Yi, J. Diaz, and M. Razeghi

Appl. Phys. Lett. 70, 443 (1997); http://dx.doi.org/10.1063/1.118176 (3 pages) | Cited 23 times

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A compressively strained InAsSb/InAs multiple quantum-well (MQW) structure was grown by low-pressure metal-organic chemical vapor deposition. Maximum output power (from two facets) up to 1 W with differential efficiency about 70% was obtained from a MQW laser with stripe width of 100 μm and cavity length of 700 μm for emitting wavelength of 3.65 μm at 90 K in pulse mode operation. About 2 times lower threshold current density was obtained from the MQW lasers for a temperature range of 90 to 140 K compared to the double heterostructure lasers grown on the same growth conditions. © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.66.Fd III-V semiconductors
78.45.+h Stimulated emission

Optical transition in SiGe self-organized dots

H. Chen, W. Q. Cheng, X. G. Xie, Q. Huang, and J. M. Zhou

Appl. Phys. Lett. 70, 446 (1997); http://dx.doi.org/10.1063/1.118177 (3 pages) | Cited 7 times

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It is found that the SiGe alloy self-organizers into uniform quantum dots embedded in the Si layer during the growth of a strained Si/Ge short period superlattice on a Si(001) substrate at a temperature of 800 °C by molecular beam epitaxy. The peak of photoluminescence from the quantum dots is at an energy higher than the band gap of Si. The intensity is two orders of magnitude higher than that of SiGe/Si quantum well. © 1997 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators

Scanning tunneling microscopy of the atomic structure of the GaAs (110) surface at reduced tip sample separation

A. J. Heinrich, M. Wenderoth, M. A. Rosentreter, M. A. Schneider, and R. G. Ulbrich

Appl. Phys. Lett. 70, 449 (1997); http://dx.doi.org/10.1063/1.118314 (3 pages) | Cited 9 times

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A scanning tunneling microscope was used to study the GaAs (110) surface at small tip-sample distances of about 2–3 Å. Atomically resolved images in this new mode referred to as near contact imaging mode revealed corrugation maxima both on the As and on the Ga surface sites at one sample voltage. These dual atom images differ significantly from the simultaneously measured conventional filled-state images at larger tunneling gap widths of 4–9 Å which show the As sublattice only. We interpret the dual atom images in terms of local tip induced modifications of the electronic surface states. These modifications are dragged along the surface with the scanning movement of the tip. © 1997 American Institute of Physics.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.20.At Surface states, band structure, electron density of states

Indium doping of CdTe polycrystalline films prepared by co-sputtering of CdTe–In–Cd targets

M. Becerril, O. Zelaya-Angel, R. Ramírez-Bon, F. J. Espinoza-Beltrán, and J. González-Hernández

Appl. Phys. Lett. 70, 452 (1997); http://dx.doi.org/10.1063/1.118178 (3 pages) | Cited 6 times

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Indium doped CdTe polycrystalline films were grown on Corning glass substrates at room temperature by co-sputtering from a CdTe–Cd–In target. The elemental Cd and In were glued onto the CdTe target covering small areas. The electrical, structural, and optical properties were analyzed as a function of the concentration of both elements. It was found that when Cd and In are simultaneously incorporated, the electrical resistivity drops and the carrier concentration increases. In both cases the changes are of several orders of magnitude. From the results, we conclude that, using this deposition technique, n-type In doped CdTe polycrystalline films can be produced. © 1997 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors
81.15.Cd Deposition by sputtering

Photoluminescence study of p-type CdGeAs2 ordered semiconductor crystals

J. E. McCrae, R. L. Hengehold, Y. K. Yeo, M. C. Ohmer, and P. G. Schunemann

Appl. Phys. Lett. 70, 455 (1997); http://dx.doi.org/10.1063/1.118179 (3 pages) | Cited 8 times

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Results of a photoluminescence (PL) study as a function of excitation laser power, sample temperature, crystal orientation, and polarization are reported for the nonlinear optical material CdGeAs2. One broad weak PL peak near 0.38 eV, and another somewhat narrower and often far brighter PL peak near 0.55 eV were found at 4 K. The high energy PL peak shifts first towards lower, then higher, and back to lower energies again as the temperature increases from 2.2 to 295 K. This high energy peak is attributed to donor–acceptor pair dominant transitions at low temperatures, but it is attributed to band-to-band dominant transitions at higher temperatures. Strongly polarized PL was observed with the E field of the PL parallel to the material’s c axis, and a polarization ratio as high as 6:1 was obtained. © 1997 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
42.70.Mp Nonlinear optical crystals

Depletion-type thin-film transistors with a ferroelectric insulator

M. W. J. Prins, S. E. Zinnemers, J. F. M. Cillessen, and J. B. Giesbers

Appl. Phys. Lett. 70, 458 (1997); http://dx.doi.org/10.1063/1.118180 (3 pages) | Cited 46 times

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We present a study of electrical characteristics of ferroelectric field-effect transistors made of PbZr0.2Ti0.8O3 and SnO2:Sb thin films. Due to properly chosen semiconductor parameters, the transistor channel can be totally depleted by the ferroelectric charge displacement. The observed remnant on/off ratio of the channel current amounts to 7×103. Pulse response measurements give information on data retention, device speed, and the occurrence of charge injection. The results lead to important design considerations for ferroelectric transistors. © 1997 American Institute of Physics.
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85.30.Tv Field effect devices
77.22.Ej Polarization and depolarization
73.61.Le Other inorganic semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Effect of hydrogen on the indium incorporation in InGaN epitaxial films

E. L. Piner, M. K. Behbehani, N. A. El-Masry, F. G. McIntosh, J. C. Roberts, K. S. Boutros, and S. M. Bedair

Appl. Phys. Lett. 70, 461 (1997); http://dx.doi.org/10.1063/1.118181 (3 pages) | Cited 51 times

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The InN percent in metalorganic chemical vapor deposition (MOCVD) and atomic layer epitaxy (ALE) grown InGaN was found to be significantly influenced by the amount of hydrogen flowing into the reactor. The temperature ranges for this study are 710–780 °C for MOCVD, and 650–700 °C for ALE. For a given set of growth conditions, an increase of up to 25% InN in InGaN, as determined by x-ray diffraction, can be achieved by reducing the hydrogen flow from 100 to 0 sccm. Additionally, the hydrogen produced from the decomposition of ammonia does not seem to change the InN percent in the films, indicating that the ammonia decomposition rate is less than 0.1%. The phenomenon of having hydrogen control the indium incorporation was not reported in the growth of any other III–V compound previously studied. © 1997 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Dd Experimental determination of defects by diffraction and scattering

Ultra-low resistive ohmic contacts on n-GaN using Si implantation

Jinwook Burm, Kenneth Chu, William A. Davis, William J. Schaff, Lester F. Eastman, and Tyler J. Eustis

Appl. Phys. Lett. 70, 464 (1997); http://dx.doi.org/10.1063/1.118182 (3 pages) | Cited 60 times

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Implanted ohmic contacts were made on molecular beam epitaxy grown GaN materials. Si was implanted at a doping density of about 4×1020  cm-3 to decrease the contact resistance of the contact, followed by an activation anneal at 1150 °C for 30 s. The overlay metal Ti/Au was evaporated. Four-probe measurements were performed on transmission line model patterns. The measured maximum contact resistance was 0.097 Ω mm and the apparent specific contact resistance was 3.6×10−8 Ω cm2. © 1997 American Institute of Physics.
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73.40.Cg Contact resistance, contact potential
73.40.Ns Metal-nonmetal contacts
61.72.uj III-V and II-VI semiconductors

Optical properties of GaN grown on ZnO by reactive molecular beam epitaxy

F. Hamdani, A. Botchkarev, W. Kim, H. Morkoç, M. Yeadon, J. M. Gibson, S.-C. Y. Tsen, David J. Smith, D. C. Reynolds, D. C. Look, K. Evans, C. W. Litton, W. C. Mitchel, and P. Hemenger

Appl. Phys. Lett. 70, 467 (1997); http://dx.doi.org/10.1063/1.118183 (3 pages) | Cited 52 times

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High quality wurtzite GaN epilayers have been grown on ZnO(0001) substrates by reactive molecular beam epitaxy. Photoluminescence and reflectivity measurements point to high quality presumably due to the near match of both the crystal lattice parameter and the stacking order between GaN and ZnO. In addition, the good films lack the characteristic yellow photoluminescence band. Any misorientation of the GaN epilayer planes with respect to the ZnO substrate is not detectable with polarized reflectivity. The x-ray double crystal diffraction measurements indicate this misorientation is much smaller than those for GaN epilayers on SiC and Al2O3 . © 1997 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.40.Fy Semiconductors

A model for visible photon emission from reverse-biased silicon p-n junctions

Amjad T. Obeidat, Zaven Kalayjian, Andreas G. Andreou, and Jacob B. Khurgin

Appl. Phys. Lett. 70, 470 (1997); http://dx.doi.org/10.1063/1.118184 (2 pages) | Cited 19 times

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We report visible (380–650 nm) electroluminescence from reverse-biased silicon p-n junctions and from n- and p-type field-effect transistors designed for a standard chip-fabrication process. We measured the spectra of over 40 junctions and devices and found that they differed from previously reported silicon electroluminescence spectra. We use a hot carrier recombination model and account for Fabry-Perot effects to explain the observed electroluminescence spectrum. Our model’s prediction is in good agreement with the measured spectra. © 1997 American Institute of Physics.
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78.60.Fi Electroluminescence
85.60.Bt Optoelectronic device characterization, design, and modeling

Optical studies of Ge islanding on Si(111)

P. D. Persans, P. W. Deelman, K. L. Stokes, L. J. Schowalter, A. Byrne, and T. Thundat

Appl. Phys. Lett. 70, 472 (1997); http://dx.doi.org/10.1063/1.118169 (3 pages) | Cited 17 times

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We report an experimental study of the optical properties of island layers resulting from molecular beam epitaxial deposition of Ge on Si(111) substrates. The combination of electroreflectance spectroscopy of the E1 transition and Raman scattering allows us to separately determine the strain and composition of the islands. For deposition at 500 °C a deposited layer of 1.36 nm of Ge assembles into 80 nm diameter islands 11 nm thick. The average Si impurity content in the islands is 2.5% while the average in-plane strain is 0.5%. Both strain and Si impurity content in islands decrease with increasing Ge deposition. © 1997 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials

Technique for measurement of the minority carrier mobility with a bipolar junction transistor

S. L. D’Souza, M. R. Melloch, M. S. Lundstrom, and E. S. Harmon

Appl. Phys. Lett. 70, 475 (1997); http://dx.doi.org/10.1063/1.118185 (3 pages) | Cited 3 times

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A simple technique to measure the minority carrier mobility using a bipolar junction transistor is demonstrated. By fixing the base-emitter voltage, the carrier injection into the base is constant. The collector current is then monitored as a function of a magnetic field applied perpendicular to the current transport across the base. The magnetic field leads to an increase in base transit time and a corresponding decrease in collector current. From the resulting fractional change in collector current, the minority carrier mobility in the base can be determined. For narrow base transistors, quasiballistic transport across the base must be taken into account when determining the bulk minority carrier mobility. © 1997 American Institute of Physics.
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85.30.De Semiconductor-device characterization, design, and modeling
85.30.Pq Bipolar transistors
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Ey III-V and II-VI semiconductors
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