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27 Oct 2003

Volume 83, Issue 17, pp. 3447-3628

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 3453 (2003); http://dx.doi.org/10.1063/1.1622431 (3 pages)

Giacomo Scalari, Stéphane Blaser, Lassaad Ajili, Jérôme Faist, Harvey Beere, Edmund Linfield, David Ritchie, and Giles Davies
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Single-crystal organic field effect transistors with the hole mobility ∼ 8 cm2/V s

V. Podzorov, S. E. Sysoev, E. Loginova, V. M. Pudalov, and M. E. Gershenson

Appl. Phys. Lett. 83, 3504 (2003); http://dx.doi.org/10.1063/1.1622799 (3 pages) | Cited 121 times

Online Publication Date: 20 October 2003

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We report on the fabrication and characterization of single-crystal organic p-type field-effect transistors (OFETs) with the field-effect mobility μ ∼ 8 cm2/V s, substantially higher than that observed in thin-film OFETs. The single-crystal devices compare favorably with thin-film OFETs not only in this respect: the mobility for the single-crystal devices is nearly independent of the gate voltage and the field effect onset is very sharp. The subthreshold slope as small as S = 0.85 V/decade has been observed for a gate insulator capacitance Ci = 2±0.2 nF/cm2. This corresponds to the intrinsic subthreshold slope Si ≡ SCi at least one order of magnitude smaller than that for the best thin-film OFETs and amorphous hydrogenated silicon (α-Si:H) devices. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Ee Mobility edges; hopping transport
72.80.Le Polymers; organic compounds (including organic semiconductors)

Photoluminescence of GaN deposited on single-crystal bulk AlN with different polarities

G. Tamulaitis, I. Yilmaz, M. S. Shur, R. Gaska, C. Chen, J. Yang, E. Kuokstis, A. Khan, S. B. Schujman, and L. J. Schowalter

Appl. Phys. Lett. 83, 3507 (2003); http://dx.doi.org/10.1063/1.1623322 (3 pages) | Cited 5 times

Online Publication Date: 20 October 2003

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Photoluminescence (PL) properties of two GaN epilayers grown in identical conditions on substrates of Al face and N face of bulk single-crystal AlN are studied in the temperature range from 8 to 300 K under weak cw excitation and strong pulsed excitation up to the intensities when electron–hole heating and stimulated emission are observed. At low temperatures and pump intensities, PL of GaN on Al-face AlN is consistent with that of homoepitaxial Ga-face GaN, while GaN on N-face AlN exhibits features indicating the existence of tail localized states. At carrier densities high enough for band-to-band transitions to dominate, the room-temperature PL of GaN on N-face AlN is higher than that in GaN on Al-face AlN due to longer effective lifetime of photoexcited carriers. © 2003 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.45.+h Stimulated emission

Light-induced narrowing of excitonic absorption lines in GaN

P. Trautman, K. Pakuła, R. Bożek, and J. M. Baranowski

Appl. Phys. Lett. 83, 3510 (2003); http://dx.doi.org/10.1063/1.1622788 (3 pages) | Cited 2 times

Online Publication Date: 20 October 2003

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The fundamental absorption edge of GaN has been investigated in GaN/AlxGa1−xN heterostructures. A broad excitonic line is observed after the sample has been cooled in darkness. A metastable narrowing occurs and three excitonic absorption lines are observed after the sample has been illuminated. Measurements of this effect have been made as a function of temperature and photon energy. It seems that the broadening is induced by an electric field present around dislocations in GaN. This field is reduced by free carriers created during illumination, which results in narrowing of the excitonic lines. © 2003 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
71.55.Eq III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.35.-y Excitons and related phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors

Formation of low resistance and transparent ohmic contacts to p-type GaN using Ni–Mg solid solution

June-O Song, Dong-Seok Leem, and Tae-Yeon Seong

Appl. Phys. Lett. 83, 3513 (2003); http://dx.doi.org/10.1063/1.1622984 (3 pages) | Cited 36 times

Online Publication Date: 20 October 2003

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We report on the formation of Ni–Mg solid solution/Au ohmic contacts on p-GaN (5×1017 cm−3). The as-deposited Ni–Mg solid solution (8 nm)/Au (8 nm) contact shows near-linear I–V characteristics. However, oxidizing the contacts at 450 and 550 °C for 1 min in air results in a dramatic improvement in their I–V behaviors, producing specific contact resistance of ∼ 10−6 Ω cm2, which is much better than the conventional oxidized Ni/Au contacts. The light transmittance of the Ni–Mg solid solution/Au contacts annealed at 550 °C is measured to be better than 79% at a wavelength of 460 nm. Based on the I–V measurements, Auger electron spectroscopy, and x-ray photoemission spectroscopy results, possible ohmic formation mechanisms are described. © 2003 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
81.05.Ea III-V semiconductors
81.05.Bx Metals, semimetals, and alloys
61.72.Cc Kinetics of defect formation and annealing
73.40.Cg Contact resistance, contact potential

Characterization of 7-nm-thick strained Ge-on-insulator layer fabricated by Ge-condensation technique

Shu Nakaharai, Tsutomu Tezuka, Naoharu Sugiyama, Yoshihiko Moriyama, and Shin-ichi Takagi

Appl. Phys. Lett. 83, 3516 (2003); http://dx.doi.org/10.1063/1.1622442 (3 pages) | Cited 79 times

Online Publication Date: 20 October 2003

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A strained Ge-on-insulator (GOI) structure with a 7-nm-thick Ge layer was fabricated for applications to high-speed transistors. The GOI layer was formed by thermal oxidation of a strained SiGe layer grown epitaxially on a silicon-on-insulator (SOI) wafer. In transmission electron microscopy measurements, the obtained GOI layer exhibited a single-crystal structure with the identical orientation to an original SOI substrate and a smooth Ge/SiO2 interface. The rms of the surface roughness of the GOI layer was evaluated to be 0.4 nm by atomic force microscopy. The residual Si fraction in the GOI layer was estimated to be lower than the detection limit of Raman spectroscopy of 0.5% and also than the electron energy loss spectroscope measurements of 3%. It was found that the obtained GOI layer was compressively strained with a strain of 1.1%, which was estimated by the Raman spectroscopy. Judging from the observed crystal quality and the strain value, this technique is promising for fabrication of high-mobility strained Ge channel of high-performance GOI metal–insulator–semiconductor (MIS) transistors. © 2003 American Institute of Physics.
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81.65.Mq Oxidation
68.55.A- Nucleation and growth
68.47.Fg Semiconductor surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)
78.30.Hv Other nonmetallic inorganics
79.20.Uv Electron energy loss spectroscopy
68.35.Ct Interface structure and roughness
68.60.Bs Mechanical and acoustical properties

Cyclotron resonance at microwave frequencies in two-dimensional hole system in AlGaAs/GaAs quantum wells

W. Pan, K. Lai, S. P. Bayrakci, N. P. Ong, D. C. Tsui, L. N. Pfeiffer, and K. W. West

Appl. Phys. Lett. 83, 3519 (2003); http://dx.doi.org/10.1063/1.1623008 (3 pages) | Cited 19 times

Online Publication Date: 20 October 2003

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Cyclotron resonance at the microwave frequency is used to measure the band edge mass (mb) in the two-dimensional hole (2DH) system, confined in 30 nm quantum wells in the Al0.1Ga0.9As/GaAs/Al0.1Ga0.9As heterostructures. We find that for 2DH density p ⩽ 1.0×1010 cm−2, mb is nearly constant, ∼ 0.35me. It increases with increasing density, to ∼ 0.5me at p = 7.4×1010 cm−2. © 2003 American Institute of Physics.
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73.21.Fg Quantum wells
73.20.At Surface states, band structure, electron density of states
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Donor–donor binding in semiconductors: Engineering shallow donor levels for ZnTe

A. Janotti, Su-Huai Wei, and S. B. Zhang

Appl. Phys. Lett. 83, 3522 (2003); http://dx.doi.org/10.1063/1.1622791 (3 pages) | Cited 7 times

Online Publication Date: 20 October 2003

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In the past, codoping by mixing donors with acceptors has been proposed to lower the dopant ionization energy. However, the level repulsion between donor and acceptor states is weak due to symmetry considerations. Here, we propose an innovative approach to lower the donor ionization energy by combining donor with donor. Using first-principles band structure method, we demonstrated this concept with n-type doping in ZnTe. For example, we find that the BrTe–SnZn pair has a binding energy of 0.9 eV and a shallow ϵ(+/0) donor level at 70 meV below the conduction-band minimum, compared to 240 meV for the isolated BrTe impurity. © 2003 American Institute of Physics.
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71.55.Gs II-VI semiconductors
71.15.Nc Total energy and cohesive energy calculations
71.15.-m Methods of electronic structure calculations
71.20.Nr Semiconductor compounds

On the nitrogen vacancy in GaN

D. C. Look, G. C. Farlow, P. J. Drevinsky, D. F. Bliss, and J. R. Sizelove

Appl. Phys. Lett. 83, 3525 (2003); http://dx.doi.org/10.1063/1.1623009 (3 pages) | Cited 30 times

Online Publication Date: 20 October 2003

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The dominant electrically active defect produced by 0.42 MeV electron irradiation in GaN is a 70 meV donor. Since only N-sublattice displacements can be produced at this energy, and since theory predicts that the N interstitial is a deep acceptor in n-type GaN, we argue that the 70 meV donor is most likely the isolated N vacancy. The background shallow donors, in the 24–26 meV range, actually decrease in concentration, probably due to interactions with mobile N interstitials that are produced by the irradiation. Thus, the recent assignment of a photoluminescence (PL) line as an exciton bound to a 25 meV N-vacancy donor is incompatible with our results. Moreover, we do not observe that PL line in our sample. © 2003 American Institute of Physics.
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71.55.Eq III-V semiconductors
61.72.J- Point defects and defect clusters
81.05.Ea III-V semiconductors
61.80.Fe Electron and positron radiation effects
78.55.Cr III-V semiconductors
61.82.Fk Semiconductors
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