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19 May 1997

Volume 70, Issue 20, pp. 2641-2767

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Near-infrared and visible photoluminescence from argon plasma polymerized fullerene film

Can Xu, Guanghua Chen, Erqing Xie, and Jinlong Gong

Appl. Phys. Lett. 70, 2641 (1997); http://dx.doi.org/10.1063/1.118983 (3 pages) | Cited 2 times

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Oxygenated polymeric fullerene films synthesized in argon plasma show strong photoluminescence in near-infrared and visible region (1.50–2.36 eV) at room temperature excited by a 514.5 nm argon ion laser. After being annealed at different high temperatures, photoluminescence decreased in intensity. The generation and decrease of the photoluminescence were explained in terms of the change of the fullerene C60 symmetry. © 1997 American Institute of Physics.
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78.66.Tr Fullerenes and related materials
78.55.Kz Solid organic materials
82.35.-x Polymers: properties; reactions; polymerization

Cryogenic picosecond sampling using fiber-coupled photoconductive switches

S. Verghese, N. Zamdmer, Qing Hu, and A. Förster

Appl. Phys. Lett. 70, 2644 (1997); http://dx.doi.org/10.1063/1.119011 (3 pages) | Cited 2 times

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A photoconductive sampling technique was developed that is well suited to probing cryogenic devices such as mesoscopic devices. Low-temperature-grown GaAs photoconductive switches were embedded in a coplanar waveguide and illuminated with pigtailed optical fibers. The chip was conduction cooled in a liquid helium cryostat. The fiber-coupled switches were designed to minimize external infrared-radiation loading and to obtain efficient optical to electrical conversion. Measurements at 300, 77, and 4.2 K demonstrate very low thermal loading and a temporal resolution of 4.7 ps—arising from dispersion of the femtosecond pulses (λ = 810nm) in the optical fiber. © 1997 American Institute of Physics.
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42.81.Dp Propagation, scattering, and losses; solitons
78.47.-p Spectroscopy of solid state dynamics
84.30.Ng Oscillators, pulse generators, and function generators
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Photon tunneling from an optically manipulated microsphere to a surface by lasing spectral analysis

Keiji Sasaki, Hideki Fujiwara, and Hiroshi Masuhara

Appl. Phys. Lett. 70, 2647 (1997); http://dx.doi.org/10.1063/1.118984 (3 pages) | Cited 18 times

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Photon tunneling of lasing emission from a dye-doped microspherical particle to an object was investigated by use of a microspectroscopy system combined with a laser manipulation technique. An emission spectrum drastically changed with approaching the lasing microsphere to a glass plate. The intensity ratio between resonant peaks exhibited exponential dependence on the sphere-object distance, whose decay constant agreed with the penetration depth of an evanescent field just outside of the microsphere. The variation in the spectral profile can be explained with the Mie scattering theory. Applicability of the lasing microsphere as a probe of a near-field scanning optical microscope is discussed. © 1997 American Institute of Physics.
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78.66.Vs Fine-particle systems
42.55.Sa Microcavity and microdisk lasers
07.79.Fc Near-field scanning optical microscopes

80 W cw TEM00 1064 nm beam generation by use of a laser-diode-side-pumped Nd:YAG rod laser

Susumu Konno, Shuichi Fujikawa, and Koji Yasui

Appl. Phys. Lett. 70, 2650 (1997); http://dx.doi.org/10.1063/1.118985 (2 pages) | Cited 14 times

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We have demonstrated stable and efficient 80 W cw TEM00 operation (M2 = 1.1) of a diode-side-pumped Nd:YAG rod laser. The laser has a simple and scalable configuration consisting of a diffusive pumping reflector and a polarization-dependent bifocusing compensation. © 1997 American Institute of Physics.
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42.55.Xi Diode-pumped lasers
42.60.Pk Continuous operation

Effect of carrier diffusion in oxidized vertical-cavity surface-emitting lasers determined from lateral spontaneous emission

J. H. Shin, H. E. Shin, and Y. H. Lee

Appl. Phys. Lett. 70, 2652 (1997); http://dx.doi.org/10.1063/1.118986 (3 pages) | Cited 8 times

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The effect of carrier diffusion on threshold current is studied quantitatively for the oxide-aperturbed 780 nm vertical-cavity surface-emitting lasers (VCSEL) from the measured spontaneous emission. The oxide aperture size of 2–10 μm is prepared and characterized. The diffusion coefficient of 4.6 cm2/s and the nonradiative recombination coefficient of 6.8×107/s are obtained using the independence of the nonradiative recombination coefficient on the laser aperture size. The contribution of carrier diffusion loss is 42% of the threshold current for the 2 μm VCSEL. The relative contribution of the diffusion becomes smaller for the larger devices as is expected. © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
73.50.Dn Low-field transport and mobility; piezoresistance

Quasiphase matched surface emitting second harmonic generation in periodically reversed asymmetric GaAs/AlGaAs quantum well waveguide

A. Fiore, Y. Beaulieu, S. Janz, J. P. McCaffrey, Z. R. Wasilewski, and D. X. Xu

Appl. Phys. Lett. 70, 2655 (1997); http://dx.doi.org/10.1063/1.118987 (3 pages) | Cited 7 times

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We experimentally demonstrate surface-emitting second harmonic generation in a waveguide containing asymmetric coupled GaAs/AlGaAs quantum wells. The nonlinear conversion efficiency is enhanced by reversing the asymmetric well orientation every coherence length, in order to quasiphase match the vertical second harmonic generation process. The measured spectrum of the asymmetric quantum well susceptibility is dominated by an excitonic peak at a pump frequency corresponding to half of the first electron-heavy hole transition energy. © 1997 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Wi Nonlinear waveguides
78.66.Fd III-V semiconductors

Using an elastomeric phase mask for sub-100 nm photolithography in the optical near field

John A. Rogers, Kateri E. Paul, Rebecca J. Jackman, and George M. Whitesides

Appl. Phys. Lett. 70, 2658 (1997); http://dx.doi.org/10.1063/1.118988 (3 pages) | Cited 112 times

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Bringing an elastomeric phase mask into conformal contact with a layer of photoresist makes it possible to perform photolithography in the near field of the mask. This technique provides an especially simple method for forming features with sizes of 90–100 nm in photoresist: straight lines, curved lines, and posts, on both curved and planar surfaces. It combines experimental convenience, new optical characteristics, and applicability to nonplanar substrates into a new approach to fabrication. Nanowire polarizers for visible light illustrate one application for this technique. © 1997 American Institute of Physics.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer

Experimental evidence of single round-trip oscillation in polarization self-modulated vertical-cavity surface emitting lasers

G. Ropars, P. Langot, M. Brunel, M. Vallet, F. Bretenaker, A. Le Floch, and K. D. Choquette

Appl. Phys. Lett. 70, 2661 (1997); http://dx.doi.org/10.1063/1.118982 (3 pages) | Cited 9 times

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The polarizations and frequencies of the two eigenstates of a vertical cavity surface emitting laser with an external cavity containing a quarter-wave plate are theoretically and experimentally analyzed. It is shown that the polarizations of these eigenstates are fixed by the neutral axes of the quarter-wave plate. The optical pulses at a frequency equal to a half of the free spectral range of the external cavity, observed through a linear polarizer, are due to beats between the two eigenstates. All these features show that such polarization self-modulated lasers oscillate in a single round trip. © 1997 American Institute of Physics.  
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42.55.Px Semiconductor lasers; laser diodes
42.60.Rn Relaxation oscillations and long pulse operation

White light from InGaN/conjugated polymer hybrid light-emitting diodes

Fumitomo Hide, Peter Kozodoy, Steven P. DenBaars, and Alan J. Heeger

Appl. Phys. Lett. 70, 2664 (1997); http://dx.doi.org/10.1063/1.118989 (3 pages) | Cited 79 times

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We report white light emission from InGaN/conjugated polymer hybrid light-emitting diodes (LEDs). White light sources (or sources with various colors) are achieved by combining the photoluminescence (PL) from semiconducting (conjugated) polymers with the emission from high efficiency InGaN based LEDs; the InGaN based LED provides the blue component and, simultaneously, serves as the short wavelength pump source for exciting the PL of the polymer film(s). © 1997 American Institute of Physics.
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42.70.Jk Polymers and organics
85.60.Jb Light-emitting devices

Contrast of microwave near-field microscopy

B. Knoll, F. Keilmann, A. Kramer, and R. Guckenberger

Appl. Phys. Lett. 70, 2667 (1997); http://dx.doi.org/10.1063/1.119255 (3 pages) | Cited 52 times

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Constant-height scanning is demonstrated to improve near-field microscopy by eliminating artifacts connected with topography scanning, hence, to image the inherent electromagnetic contrast. Microwaves are chosen for this study because the long wavelength eliminates coherence artifacts, owing to a scale separation of wave and image frequencies. Measured amplitude and phase images of conductive films are quantitatively analyzed by considering the longitudinal electric near field. The observed spatial resolution of 200 nm equals the probing tip size and proves that the skin depth δ of the tip material (here, 1600 nm) presents no resolution limit to scanning optical microscopy. © 1997 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
42.30.Va Image forming and processing

Distributed feedback quantum cascade lasers

Jérome Faist, Claire Gmachl, Federico Capasso, Carlo Sirtori, Deborah L. Sivco, James N. Baillargeon, and Alfred Y. Cho

Appl. Phys. Lett. 70, 2670 (1997); http://dx.doi.org/10.1063/1.119208 (3 pages) | Cited 121 times

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See Also: Erratum

Show Abstract
Pulsed single mode operation of distributed feedback quantum cascade lasers is reported above room temperature at both 5.4 and 8 μm wavelengths. Peak optical powers up to 60 mW at 300 K are obtained with a tuning range of ∼60 nm from 100 to ∼320 K. The linewidth is limited by thermal drift during the pulse with a typical value of 0.3 cm−1 for a 10 ns long pulse at 300 K. © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking

Polarimetry of thin metal transmission gratings in the resonance region and its impact on the response of metal-semiconductor-metal photodetectors

Erli Chen and Stephen Y. Chou

Appl. Phys. Lett. 70, 2673 (1997); http://dx.doi.org/10.1063/1.118990 (3 pages) | Cited 7 times

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The resonance behavior of metal transmission gratings and its impact on the response of metal-semiconductor-metal (MSM) photodetectors have been studied experimentally and theoretically. The metal gratings, with finger spacings in the subwavelength region of the visible light, were fabricated using e-beam lithography and lift-off. Strong resonances have been observed only in the S polarization. As a result, the light transmitted through a grating is primarily S polarized if the grating’s finger spacing is less than one-third of the wavelength of the incident light, but P polarized otherwise. Similar phenomenon has been observed in the response of MSM photodetectors since the fingers (electrodes) of an MSM photodetector basically form a grating. Theoretical simulations employing the rigorous modal-expansion theory fairly predict the observed phenomenon. © 1997 American Institute of Physics.
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73.40.Sx Metal-semiconductor-metal structures
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Dj Gratings

Laser-induced generation of pure tensile stresses

M. H. Niemz, C. P. Lin, C. Pitsillides, J. Cui, A. G. Doukas, and T. F. Deutsch

Appl. Phys. Lett. 70, 2676 (1997); http://dx.doi.org/10.1063/1.118991 (3 pages)

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While short compressive stresses can readily be produced by laser ablation, the generation of pure tensile stresses is more difficult. We demonstrate that a 90° prism made of polyethylene can serve to produce short and pure tensile stresses. A compressive wave is generated by ablating a thin layer of strongly absorbing ink on one surface of the prism with a Q-switched frequency-doubled Nd:YAG laser. The compressive wave driven into the prism is reflected as a tensile wave by the polyethylene-air interface at its long surface. The low acoustic impedance of polyethylene makes it ideal for coupling tensile stresses into liquids. In water, tensile stresses up to −200 bars with a rise time of the order of 20 ns and a duration of 100 ns are achieved. The tensile strength of water is determined for pure tensile stresses lasting for 100 ns only. The technique has potential application in studying the initiation of cavitation in liquids and in comparing the effect of compressive and tensile stress transients on biological media. © 1997 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
81.40.Lm Deformation, plasticity, and creep
42.62.Be Biological and medical applications
43.25.Yw Nonlinear acoustics of bubbly liquids

Carbon nanotubes are coherent electron sources

Heinz Schmid and Hans-Werner Fink

Appl. Phys. Lett. 70, 2679 (1997); http://dx.doi.org/10.1063/1.118978 (2 pages) | Cited 42 times

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The observation of electron interference effects provides direct evidence of the coherence of the electrons emitted from a carbon nanotube. To demonstrate this, the low-energy electron point source microscope has been used to mount an individual carbon nanotube onto a tungsten tip. In subsequent experiments, the electrons emitted from the nanotube were used to generate holograms. Comparison with a standard tungsten atomic point source emitter establishes a high degree of coherence for a nanotube emitter. © 1997 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
79.70.+q Field emission, ionization, evaporation, and desorption
61.05.jp Electron holography

Stable amorphous-silicon thin-film transistors

H. Meiling and R. E. I. Schropp

Appl. Phys. Lett. 70, 2681 (1997); http://dx.doi.org/10.1063/1.118992 (3 pages) | Cited 24 times

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Hydrogenated amorphous silicon, a-Si:H, prepared with the hot-wire chemical vapour deposition technique is incorporated in thin-film transistors (TFTs). High-quality TFTs are fabricated with this type of a-Si:H, which we deposited at a rate of 17 Å/s. TFTs with a current switching ratio of 5×105, a threshold voltage of 6.3 V, and an electron field-effect mobility in the saturation regime of 0.6 cm2/V s are obtained. These TFTs do not show any threshold voltage shift upon prolonged gate voltage application, in contrast to conventional a-Si:H TFTs. This has been achieved by optimizing the electronic properties of the hot-wire layer, and by optimizing the interface between the gate dielectric and the hot-wire layer. © 1997 American Institute of Physics.
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85.30.Tv Field effect devices
73.61.Jc Amorphous semiconductors; glasses
81.05.Gc Amorphous semiconductors

Raman characterization of aligned carbon nanotubes produced by thermal decomposition of hydrocarbon vapor

Wenzhi Li, Hao Zhang, Chaoying Wang, Yun Zhang, Liwen Xu, Ke Zhu, and Sishen Xie

Appl. Phys. Lett. 70, 2684 (1997); http://dx.doi.org/10.1063/1.118993 (3 pages) | Cited 159 times

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Raman characterization of aligned carbon nanotubes of average diameter 10–15 nm, produced by chemical vapor deposition on a mesoporous substrate, has been carried out. The resonance behavior and higher-order Raman bands up to fourth order have been observed and compared with those of carbon nanotubes produced by arc discharge and highly oriented pyrolytic graphite, as well as pyrolytic graphite. The phonon properties have been analyzed with the help of high-resolution transmission electron microscope studies. © 1997 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
78.30.Na Fullerenes and related materials
81.05.ub Fullerenes and related materials

Direct thermal conductance measurements on suspended monocrystalline nanostructures

T. S. Tighe, J. M. Worlock, and M. L. Roukes

Appl. Phys. Lett. 70, 2687 (1997); http://dx.doi.org/10.1063/1.118994 (3 pages) | Cited 81 times

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We describe and demonstrate a new class of devices that enable direct thermal conductance measurements on monocrystalline nanostructures. These are possible through our newly developed techniques for three-dimensional, successive surface nanomachining of GaAs-based heterostructures. Our methods allow the patterning of complex devices comprising electrically insulating, mesoscopic thermal conductors with separate, thermal transducers in situ. Intimate thermal contact between these elements is provided by their epitaxial registry. Low-temperature thermal conductance measurements indicate that phonon boundary scattering in these initial nanometer is scale structures is partially specular. These devices offer promise for ultrasensitive bolometry and calorimetry. © 1997 American Institute of Physics.
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73.23.-b Electronic transport in mesoscopic systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Direct-injection high-Tc dc-SQUID with an upper YBa2Cu3O7−x ground plane

H. Terai, M. Hidaka, T. Satoh, and S. Tahara

Appl. Phys. Lett. 70, 2690 (1997); http://dx.doi.org/10.1063/1.118995 (3 pages) | Cited 12 times

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We have fabricated direct-injection high-Tc superconducting quantum interference devices (SQUIDs) with integrated YBa2Cu3O7−x (YBCO) ground planes in the upper part of structure. The YBCO/PrBa2Cu3O7−x(PBCO)/YBCO edge junctions with 10-nm-thick PBCO barriers showed RSJ-like current-voltage (I–V) characteristics before and after the ground plane formation. We measured the voltage modulations of these SQUIDs with two different hole sizes to evaluate the line inductance. At a temperature of 30 K, the estimated line inductance under the ground plane was about 1.0 pH/□, while the estimated line inductance without the ground plane was 2.8 pH/□. © 1997 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.72.-h Cuprate superconductors
74.78.Fk Multilayers, superlattices, heterostructures

Investigation of the compensation mechanism in semi-insulating GaAs from alpha-spectra studies at low temperature

J. W. Chen, D. G. Ebling, R. Geppert, R. Irsigler, Th. Schmid, M. Rogalla, J. Ludwig, and K. Runge

Appl. Phys. Lett. 70, 2693 (1997); http://dx.doi.org/10.1063/1.118981 (3 pages) | Cited 1 time

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We present the results of charge collection measurements on liquid encapsulated Czochralski grown semi-insulating GaAs devices for alpha particles. Experimental evidence is given which demonstrates a drastic enhancement of charge collection efficiency after prolonged illumination with 1.086 μm below-gap light. The recovery of EL2 from metastable state to normal state can also be achieved by electric field at high bias voltage. The experimental result shows that the EL2 defect is practically the dominant trap for free charge carriers and together with other shallow defects responsible for the electric compensation in semi-insulating GaAs. The metastable transition of the EL2 defect is always simultaneously accompanied by the neutralization of a shallow acceptor. No change in the type of conductivity was found. © 1997 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
29.40.Wk Solid-state detectors
61.80.Jh Ion radiation effects

Depth analysis of phase formation in Si after high-dose Fe ion implantation by depth-selective conversion-electron Mössbauer spectroscopy

S. Kruijer, W. Keune, M. Dobler, and H. Reuther

Appl. Phys. Lett. 70, 2696 (1997); http://dx.doi.org/10.1063/1.118996 (3 pages) | Cited 3 times

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Fe+ ions of 200 keV in energy were implanted into Si(111) at 350 °C with a dose of 7×1017 cm−2. The depth distribution of the two formed phases (ϵ-FeSi and β-FeSi2) was investigated nondestructively up to a depth of about 800 Å by depth-selective conversion-electron Mössbauer spectroscopy (DCEMS) in combination with depth-profiling (destructive) Auger electron spectroscopy (AES). Near the surface only β-FeSi2 is formed, while a mixture of β-FeSi2 and ϵ-FeSi is formed at larger depths. The Fe-concentration depth profile calculated from the DCEMS results is in good agreement with that measured by AES. © 1997 American Institute of Physics.
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61.72.uf Ge and Si
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
76.80.+y Mössbauer effect; other γ-ray spectroscopy

Correlation between dielectric breakdown and charge generation in silicon oxide films

Tetsuo Hayakawa, Yukihiko Watanabe, Hirofumi Funabashi, Yasuichi Mitsushima, and Yasunori Taga

Appl. Phys. Lett. 70, 2699 (1997); http://dx.doi.org/10.1063/1.118997 (3 pages) | Cited 1 time

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To clarify the correlation between breakdown characteristics and charge generation under high field electrical stress, we have separated the contributions of the charges generated in the oxide bulk and near the Si/SiO2 interface to oxide breakdown. It is found that the density of positive charges generated near the cathode interface increases monotonically with stress time, and that it was independent of stress conditions immediately before breakdown. No correlation between charge generation in the oxide bulk and oxide breakdown has been observed. These results are new experimental evidences which support the model showing that positive charges generated near the cathode interface are responsible for oxide breakdown. © 1997 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.22.Jp Dielectric breakdown and space-charge effects
77.55.-g Dielectric thin films

X-ray photoelectron spectroscopic evaluation of valence band offsets for strained Si1−xGex, Si1−yCy, and Si1−x−yGexCy on Si(001)

Myeongcheol Kim and H. J. Osten

Appl. Phys. Lett. 70, 2702 (1997); http://dx.doi.org/10.1063/1.118998 (3 pages) | Cited 21 times

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The crucial parameters which determine the electrical and optical behavior of a heterojunction are the valence and conduction band offsets. We demonstrate that carefully performed in situ x-ray photoelectron spectroscopic measurements allow the evaluation of valence band offsets in strained heteroepitaxial systems on Si(001). The result obtained for a Si0.75Ge0.25 alloy layer agrees very well with the known value, indicating the reliability of the used method. For Si0.977C0.023 alloy layers tensily strained on Si(001), we could not find any significant valence band offset to Si. The observed band gap narrowing is mainly dominated by a conduction band offset. Ternary strained Si0.727Ge0.25C0.023 alloy layers show the same valence band offset to Si as the appropriate binary Si0.75Ge0.25 alloy layers, that is, the valence band offset is dominated by Ge effects. © 1997 American Institute of Physics.  
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71.20.Nr Semiconductor compounds
71.70.Fk Strain-induced splitting
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.05.Cy Elemental semiconductors

Blocking effect of charge transfer at the porous silicon/silicon interface

Th. Dittrich, J. Rappich, and V. Yu. Timoshenko

Appl. Phys. Lett. 70, 2705 (1997); http://dx.doi.org/10.1063/1.118979 (3 pages) | Cited 5 times

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The photoluminescence (PL) of a thin porous silicon (por-Si) layer and of bulk c-Si is investigated in situ after the formation in 0.2 M NH4F (pH 3.2) and in water, ethanol, and their vapors. The excitation light of the used pulsed N2 laser is absorbed in the por-Si surface layer. This allows the contactless study of changes of the diffusion of excess carriers from the por-Si layer into the c-Si by using the PL of c-Si as a probe. The radiative recombination of c-Si decreases after exchanging the electrolyte by the other media while the PL intensity of the por-Si increases strongly. The strongest increase of the PL of por-Si is observed in ethanol atmosphere. The results are discussed on the basis of blocking of the out diffusion of excess carriers from the por-Si layer into the bulk c-Si due to electrical charging of interface states. © 1997 American Institute of Physics.
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78.55.Mb Porous materials
73.63.-b Electronic transport in nanoscale materials and structures

Explanation for the oxide thickness dependence of breakdown characteristics of metal-oxide-semiconductor structures

D. J. DiMaria and J. H. Stathis

Appl. Phys. Lett. 70, 2708 (1997); http://dx.doi.org/10.1063/1.118999 (3 pages) | Cited 30 times

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Experimental evidence is presented showing that the thickness dependence observed for charge-to-breakdown measurements of very thin oxide layers in metal-oxide-semiconductor structures is correlated with that for the reduction in total generated microscopic defects necessary to induce destruction. These results are related to a percolation model for the formation of paths connecting some of these defects from the cathode to the anode at the time of breakdown. © 1997 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.22.Jp Dielectric breakdown and space-charge effects

Anisotropy of the nitrogen conduction states in the group III nitrides studied by polarized x-ray absorption

K. Lawniczak-Jablonska, T. Suski, Z. Liliental-Weber, E. M. Gullikson, J. H. Underwood, R. C. C. Perera, and T. J. Drummond

Appl. Phys. Lett. 70, 2711 (1997); http://dx.doi.org/10.1063/1.119000 (3 pages) | Cited 23 times

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The energy distribution of the nitrogen antibonding electron states in the hexagonal epitaxial layers of AlN, GaN, and InN and cubic epitaxial layers of GaN and InN along pxy plane and pz direction is reported. The study was performed by the polarized x-ray absorption at the K edge of N. A strong polarization dependence of the absorption spectra indicating the significant anisotropy of the conduction band was found in the case of hexagonal samples. Very weak polarization dependencies observed in cubic samples correspond well with the defect distribution anisotropy. Qualitatively different and cation dependent antibonding states distribution point out the role played by a contribution of hybridized cation-nitrogen electronic states to the individual conduction band structures of AlN, GaN, and InN. © 1997 American Institute of Physics.
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73.61.Ey III-V semiconductors
71.20.Nr Semiconductor compounds
78.70.Dm X-ray absorption spectra
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