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14 Jun 2004

Volume 84, Issue 24, pp. 4839-5046

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 4409 (2004); http://dx.doi.org/10.1063/1.1757648 (3 pages)

Azita Soleymani, Piroz Zamankhan, and William Polashenski
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Effects of high temperature forming gas anneal on the characteristics of metal-oxide-semiconductor field-effect transistor with HfO2 gate stack

Rino Choi, Chang Seok Kang, Hag-Ju Cho, Young-Hee Kim, Mohammad S. Akbar, and Jack C. Lee

Appl. Phys. Lett. 84, 4839 (2004); http://dx.doi.org/10.1063/1.1755412 (3 pages) | Cited 12 times

Online Publication Date: 25 May 2004

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The effects of high temperature forming gas (N2:H2 = 96:4) anneal (600 °C) prior to metallization have been evaluated in terms of the improvement in the carrier mobility of HfO2/nitride layer gate stack metal-oxide-semiconductor field-effect transistors with TaN gate electrode. The high-temperature forming gas anneal has been found to be effective in improving the interface quality by lowering both interface state density and interface charges. The improvements resulting in decreased Coulombic scattering centers can be attributed to hydrogen atoms that were concentrated near the interface. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
61.72.Cc Kinetics of defect formation and annealing
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation

Critical point transitions of wurtzite AlN in the vacuum–ultraviolet spectral range

J. Chen, W. Z. Shen, H. Ogawa, and Q. X. Guo

Appl. Phys. Lett. 84, 4866 (2004); http://dx.doi.org/10.1063/1.1762694 (3 pages) | Cited 6 times

Online Publication Date: 25 May 2004

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The optical reflection spectra have been measured on a high-quality wurtzite aluminum nitride (AlN) single crystal with synchrotron radiation in the range of 6–16 eV at different temperatures. The energy positions of the dominant structures due to the critical point (CP) transitions have been extracted by employing Adachi’s dielectric function model. By the aid of the band structure of AlN, we have assigned up to ten CP transitions in the reflection spectra. The crystal-field splitting at the center of the Brilliouin zone is observed to be 110 meV. We have further revealed the temperature dependencies of these interband transitions. © 2004 American Institute of Physics.
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78.40.Fy Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)
71.20.Nr Semiconductor compounds
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
64.70.-p Specific phase transitions

Leakage mechanism in GaN and AlGaN Schottky interfaces

Tamotsu Hashizume, Junji Kotani, and Hideki Hasegawa

Appl. Phys. Lett. 84, 4884 (2004); http://dx.doi.org/10.1063/1.1762980 (3 pages) | Cited 46 times

Online Publication Date: 25 May 2004

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Based on detailed temperature-dependent current–voltage (I–V–T) measurements the mechanism of leakage currents through GaN and AlGaN Schottky interfaces is discussed. The experiments were compared to calculations based on thin surface barrier model in which the effects of surface defects were taken into account. Our simulation method reproduced the experimental I–V–T characteristics of the GaN and AlGaN Schottky diodes, and gave excellent fitting results to the reported Schottky I–V curves in GaN for both forward and reverse biases at different temperatures. The present results indicate that the barrier thinning caused by unintentional surface-defect donors enhances the tunneling transport processes, leading to large leakage currents through GaN and AlGaN Schottky interfaces. © 2004 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
72.20.Fr Low-field transport and mobility; piezoresistance
73.61.Ey III-V semiconductors

Terahertz emission due to interminiband resonant Zener tunneling in wide-miniband GaAs/Al0.3Ga0.7As superlattices

Y. Shimada, N. Sekine, and K. Hirakawa

Appl. Phys. Lett. 84, 4926 (2004); http://dx.doi.org/10.1063/1.1759382 (3 pages) | Cited 10 times

Online Publication Date: 28 May 2004

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We have investigated terahertz (THz) emission induced by high-field electron transport in biased wide-miniband GaAs/Al0.3Ga0.7As superlattices. With increasing bias electric fields, two distinct regimes are observed in the bias-field dependence of the emitted THz intensity. These two regimes are attributed to the intraminiband transport and interminiband Zener tunneling regimes, respectively. In the Zener tunneling regime, quasiperiodic structures are observed in the bias field dependence of the emitted THz intensity and are identified to be due to the resonant Zener tunneling between the Wannier–Stark ladders associated with the ground and excited minibands. © 2004 American Institute of Physics.
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73.63.-b Electronic transport in nanoscale materials and structures
72.20.Ht High-field and nonlinear effects
84.40.-x Radiowave and microwave (including millimeter wave) technology
71.20.Nr Semiconductor compounds

Measurement of spin polarization by Andreev reflection in ferromagnetic In1−xMnxSb epilayers

R. P. Panguluri, B. Nadgorny, T. Wojtowicz, W. L. Lim, X. Liu, and J. K. Furdyna

Appl. Phys. Lett. 84, 4947 (2004); http://dx.doi.org/10.1063/1.1760883 (3 pages) | Cited 12 times

Online Publication Date: 28 May 2004

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We carried out point contact Andreev reflection (PCAR) spin spectroscopy measurements on epitaxially grown ferromagnetic In1−xMnxSb epilayers with a Curie temperature of ∼9 K. The spin sensitivity of PCAR in this material was demonstrated by parallel control studies on its nonmagnetic analog, In1−yBeySb. We found the conductance curves of the Sn point contacts with In1−yBeySb to be fairly conventional, with the possible presence of proximity-induced superconductivity effects at the lowest temperatures. These measurements provided control data for subsequent PCAR measurements on ferromagnetic In1−xMnxSb, which indicated spin polarization in In1−xMnxSb to be 52±3%. © 2004 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.30.Wx Spin crossover
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
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