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15 Dec 2005

Volume 98, Issue 12, Articles (12xxxx)

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An unusual nonlinearity in current-voltage curves of a bidimensional electron gas at low temperatures

R. Khlil, A. El Hdiy, A. Cavanna, F. Laruelle, and Y. Jin

J. Appl. Phys. 98, 123701 (2005); http://dx.doi.org/10.1063/1.2141650 (5 pages) | Cited 2 times

Online Publication Date: 16 December 2005

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Electrical characterization of a bidimensional electron gas transport has been investigated. Three AlGaAs/GaAs heterostructures have been used for the study. Hall measurements have been performed at 4.2 K and current-voltage characteristics at fixed temperatures between 4.2 and 300 K. Measurements have been made using a four-point probe method. A saturation of the current at weak electric fields was observed in the range of low temperatures (<100 K). The channel conductivity, the contact resistance, the electron mobility and the bidimensional electron gas density were determined. Electron drift velocities were deduced from current-voltage curves at the beginning of the saturation regime at 4.2 K and compared with those found in the literature. The saturation, giving weak velocity, is related to impurity and alloy scatterings. Drift velocities close to the Fermi velocity are related to the Gunn effect. A Schottky effect has been observed at low temperatures (<100 K) when the electron transport is perpendicular to the direction leading to the saturation of the current. This Schottky behavior indicates degradation of Ohmic contacts in the Au/Ni/Ge structure constituting the source and the drain.
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73.40.−c
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
73.40.Cg Contact resistance, contact potential

One-dimensional photonic crystals based on porous n-type silicon

T. V. Murzina, F. Yu. Sychev, E. M. Kim, E. I. Rau, S. S. Obydena, O. A. Aktsipetrov, M. A. Bader, and G. Marowsky

J. Appl. Phys. 98, 123702 (2005); http://dx.doi.org/10.1063/1.2142075 (4 pages) | Cited 6 times

Online Publication Date: 16 December 2005

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Photonic crystals (PC) based on porous n‐Si are fabricated and their structural, optical, and nonlinear optical properties are studied. The n‐Si based PC composed of five pairs of layers with alternate porosity reveal a rather broad photonic band gap (PBG) of more than 100 nm and a reflectivity of up to 0.75. An average pore diameter of approximately 90 nm is found in n‐Si based PC in contrast to mesoporous p‐Si based PC, where pores are approximately 15 nm in diameter. Second-harmonic generation (SHG) spectroscopy reveals the enhancement of the SHG intensity by a factor of 102 at the blue edge of the PBG spectra which is attributed to the fulfillment of the phase matching conditions and the localization of the fundamental optical field in the PC.
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42.70.Qs Photonic bandgap materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Impact of nitrogen incorporation on interface states in (100)Si/HfO2

Y. G. Fedorenko, L. Truong, V. V. Afanas’ev, A. Stesmans, Z. Zhang, and S. A. Campbell

J. Appl. Phys. 98, 123703 (2005); http://dx.doi.org/10.1063/1.2140871 (9 pages) | Cited 8 times

Online Publication Date: 21 December 2005

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The influence of nitrogen incorporation on the energy distribution of interface states in the (100)Si/HfO2 system and their passivation by hydrogen has been studied as compared to N-free samples. The nitrogen in the (100)Si/HfO2 entity is found to increase the trap density, most significantly, in the upper part of the Si band gap, in which energy range N prevents passivation of interface traps by hydrogen. At the same time, passivation of fast interface traps in the lower part of the band gap proceeds efficiently, provided the thickness of the nitrogen-containing interlayer is kept within a few monolayers. The minimal interface trap density below the midgap achieved after passivation in H2 is determined by the presence of slow N-related states, likely located in the insulator. As inferred from capacitance-voltage and ac conductance analysis, the lowest density of electrically active defects [(8–9)×1010 eV−1 cm−2 at 0.4–0.5 eV from the top of the Si valence band edge] is achieved both in the N-free and N-containing (100)Si/HfO2 structures after post-deposition anneal at 800 °C in N2+5% O2 followed by passivation in molecular hydrogen at 400 °C for 30 min.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.At Surface states, band structure, electron density of states
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Photoconduction in Alq3

Debdutta Ray, Meghan P. Patankar, N. Periasamy, and K. L. Narasimhan

J. Appl. Phys. 98, 123704 (2005); http://dx.doi.org/10.1063/1.2143119 (7 pages) | Cited 6 times

Online Publication Date: 21 December 2005

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Photoelectronic properties of Alq3 were studied by photoconductivity (PC) measurements in thin film, sandwich (indium-tin-oxide/Alq3/LiF/Al) devices. We find that the photocurrent is dominated by bulk generation of carriers for incident photon energies greater than 2.75 eV. The quantum efficiency of photocarrier generation has been measured from carrier collection measurements to be about 10%. The quantum efficiency is largely independent of electric field. This enables a direct measurement of the electric field dependence of mobility using photoconductivity measurements, which is used for quantitative analysis of the dark forward current in these devices. PC measurements were also used to obtain (μ0nτn) product which can be used as a measure of material quality. For Alq3, we find that the value of (μ0nτn) product was between 3×10−15 cm2/V to 8×10−15 cm2/V for different samples. In forward bias, at high field the photocurrent shows saturation accompanied by a phase shift. These effects are attributed to space charge effects in the device.
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73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
73.50.Pz Photoconduction and photovoltaic effects
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