In the last 30 days

• Open/close High energy irradiation effects on AlGaN/GaN HFET devices

  G Sonia et al 2007 Semicond. Sci. Technol. 22 1220 Tag this article

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  The effect of proton, carbon, oxygen and krypton irradiation on AlGaN HFET devices has been studied. Irradiation was performed at 68 and 120 MeV with fluences in the range from 1 × 10 ⁷ to 1 × 10 ¹³ cm ⁻². Before and after irradiation, dc and pulsed I– V characteristics, loadpull and S-parameters of the AlGaN HFET devices were measured. A thick GaN reference layer was characterized by x-ray diffraction, photoluminescence and Hall measurements before and after irradiation. Proton, carbon and oxygen irradiation show no degradation in devices while krypton irradiation shows a small change at a fluence of 1 × 10 ¹⁰ cm ⁻² in the device characteristics. The device results are correlated with the thick GaN results.

• Open/close The status and perspectives of metal oxide thin-film transistors for active matrix flexible displays

  Jae Kyeong Jeong 2011 Semicond. Sci. Technol. 26 034008 Tag this article

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  The purpose of this paper is to give an overview of the state-of-the-art of metal oxide thin-film transistors (TFTs). First, the question of how to achieve high-performance oxide TFTs is addressed, including the exploration of new channel materials, the realization of low-resistance ohmic contacts and the implementation of high- k dielectric materials as the gate insulator. The electrical instability of the oxide TFTs is also discussed, which is critical for their application in flexible backplane electronics: special attention is given to the understanding of the degradation mechanism of oxide TFTs against bias thermal stress (BTS) and light illuminated BTS. Finally, the recent application of oxide TFTs in active matrix displays, such as electronic paper, liquid crystal displays and organic light-emitting diodes, is addressed.

• Open/close Performance modeling of MWIR InAs/GaSb/B–Al_0.2Ga_0.8Sb type-II superlattice nBn detector

  P Martyniuk et al 2012 Semicond. Sci. Technol. 27 055002 Tag this article

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  This paper reports on the unipolar medium wavelength infrared (MWIR) InAs/GaSb/B–Al _0.2Ga _0.8Sb type-II superlattice (T2SL) nBn detector's photoelectrical performance. In our model, the heterojunction barrier-active region (absorber) was assumed to be decisive as the contributing dark current mechanism limiting nBn's detector performance. The voltage drop analysis on the nBn structure was introduced to estimate the bias drop on the heterojunction barrier-active region. It was assumed that the contact n ⁺-barrier heterojunction's layer has an insignificant influence on the electrical properties of the detector. In addition, a bulk-based model with an effective band gap of T2SL material has been assumed in the device modeling. Both current–voltage ( I–V) and differential resistance–area product RA( V, T), characteristics of nBn's detector were found to be dominated by diffusion and generation–recombination currents in the zero-bias and the low-bias regions. At medium values of reverse voltages, the dark current was mostly affected by trap-assisted tunneling, whereas the band-to-band tunneling revealed its contribution at high values of reverse bias ( V > 0.7 V). The RA( V, T) characteristics' fitting procedure allowed estimation of both diffusion and generation–recombination lifetimes as well as the trap energy level temperature dependence within T2SL energy gap. It was predicted that at T = 77 K, the RA product and detectivity reached values of 1000 Ωcm ² and 4 × 10 ¹¹ cm Hz ^1/2 W ^-1, respectively. The corresponding values at room temperature were 0.01 Ωcm ² and D* = 5 × 10 ⁸ cmHz ^1/2 W ⁻¹, respectively. Finally, InAs/GaSb/B–Al _0.2Ga _0.8Sb T2SLs nBn's state of the art was compared to the performance of InAs/GaSb T2SLs PIN photodiodes and the HgCdTe bulk photodiodes operated at near-room temperature. It was shown that the RA product of the MWIR T2SLs nBn detector has reached a comparable level with the state of the art of the HgCdTe bulk photodiodes.

• Open/close Thin film encapsulation for flexible AM-OLED: a review

  Jin-Seong Park et al 2011 Semicond. Sci. Technol. 26 034001 Tag this article

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  Flexible organic light emitting diode (OLED) will be the ultimate display technology to customers and industries in the near future but the challenges are still being unveiled one by one. Thin-film encapsulation (TFE) technology is the most demanding requirement to prevent water and oxygen permeation into flexible OLED devices. As a polymer substrate does not offer the same barrier performance as glass, the TFE should be developed on both the bottom and top side of the device layers for sufficient lifetimes. This work provides a review of promising thin-film barrier technologies as well as the basic gas diffusion background. Topics include the significance of the device structure, permeation rate measurement, proposed permeation mechanism, and thin-film deposition technologies (Vitex system and atomic layer deposition (ALD)/molecular layer deposition (MLD)) for effective barrier films.

• Open/close ZnO nanorods: synthesis, characterization and applications

  Gyu-Chul Yi et al 2005 Semicond. Sci. Technol. 20 S22 Tag this article

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  This paper presents a review of current research activities on ZnO nanorods (or nanowires). We begin this paper with a variety of physical and chemical methods that have been used to synthesize ZnO nanorods (or nanowires). There follows a discussion of techniques for fabricating aligned arrays, heterostructures and doping of ZnO nanorods. At the end of this paper, we discuss a wide range of interesting properties such as luminescence, field emission, gas sensing and electron transport, associated with ZnO nanorods, as well as various intriguing applications. We conclude with personal remarks on the outlook for research on ZnO nanorods.

• Open/close Semipolar GaN grown on foreign substrates: a review

  F Scholz 2012 Semicond. Sci. Technol. 27 024002 Tag this article

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  Non- and semipolar GaN-based optoelectronic device structures have attracted much attention in recent years. Best results have been obtained on small bulk substrates cut from thick c-plane epi-wafers. However, owing to the limited size of such substrates, it is very attractive to study hetero-epitaxial approaches on foreign substrates. In this paper, we review the current state of such studies which eventually lead to large area non- or semipolar nitride structures. The simplest approach is to use planar sapphire or SiC wafers of non- c-plane orientations on which potentially less polar GaN can be grown. However, typically huge dislocation and in particular stacking fault densities evolve. More sophisticated approaches make use of the good GaN growth performance in the c-direction, eventually leading anyway to large area non- or semipolar structures. Several such approaches are discussed in this paper.

• Open/close Indium incorporation and emission wavelength of polar, nonpolar and semipolar InGaN quantum wells

  Tim Wernicke et al 2012 Semicond. Sci. Technol. 27 024014 Tag this article

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  InGaN quantum wells were grown by metal organic vapor-phase epitaxy on polar (0 0 0 1), nonpolar (1 0   0) and on semipolar (1 0   2), (1 1   2), (1 0   1) as well as (2 0   1) oriented GaN substrates. The room-temperature photoluminescence (PL) and electroluminescence (EL) emission energies for quantum wells grown on different crystal orientations show large variations of up to 600 meV. The following order of the emission energy was found throughout the entire range of growth temperatures: (1 0   1) < (1 1   2) = (0 0 0 1) < (2 0   1) < (1 0   0) = (1 0   2). In order to differentiate between the effects of strain, quantum-confined stark effect (QCSE) and indium incorporation the experimental data were compared to k.p theory-based calculations for differently oriented InGaN QWs. The major contribution to the shift between (1 0   0) and (0 0 0 1) InGaN quantum wells can be attributed to the QCSE. The redshift between (1 0   0) and the semipolar (1 0   2) and (2 0   1) QWs can be attributed to shear and anisotropic strain affecting the valence band structure. Finally, for (1 1   2) and (1 0   1) the emission energy shift could be attributed to a significantly higher indium incorporation efficiency.

• Open/close Transparent conducting oxide semiconductors for transparent electrodes

  Tadatsugu Minami 2005 Semicond. Sci. Technol. 20 S35 Tag this article

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  The present status and prospects for further development of polycrystalline or amorphous transparent conducting oxide (TCO) semiconductors used for practical thin-film transparent electrode applications are presented in this paper. The important TCO semiconductors are impurity-doped ZnO, In ₂O ₃ and SnO ₂ as well as multicomponent oxides consisting of combinations of ZnO, In ₂O ₃ and SnO ₂, including some ternary compounds existing in their systems. Development of these and other TCO semiconductors is important because the expanding need for transparent electrodes for optoelectronic device applications is jeopardizing the availability of indium-tin-oxide (ITO), whose main constituent, indium, is a very expensive and scarce material. Al- and Ga-doped ZnO (AZO and GZO) semiconductors are promising as alternatives to ITO for thin-film transparent electrode applications. In particular, AZO thin films, with a low resistivity of the order of 10 ⁻⁵ Ω cm and source materials that are inexpensive and non-toxic, are the best candidates. However, further development of the deposition techniques, such as magnetron sputtering or vacuum arc plasma evaporation, as well as of the targets is required to enable the preparation of AZO and GZO films on large area substrates with a high deposition rate.

• Open/close Using the kinetic Wulff plot to design and control nonpolar and semipolar GaN heteroepitaxy

  Benjamin Leung et al 2012 Semicond. Sci. Technol. 27 024005 Tag this article

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  For nonpolar and semipolar orientations of GaN heteroepitaxially grown on sapphire substrates, the development of growth procedures to improve surface morphology and microstructure has been driven in a largely empirical way. This work attempts to comprehensively link the intrinsic properties of GaN faceted growth, across orientations, in order to understand, design and control growth methods for nonpolar (1 1  2 0) GaN and semipolar (1 1  2 2) GaN on foreign substrates. This is done by constructing a comprehensive series of kinetic Wulff plots (or v-plots) by monitoring the advances of convex and concave facets in selective area growth. A methodology is developed to apply the experimentally determined v-plots to the interpretation and design of evolution dynamics in nucleation and island coalescence. This methodology offers a cohesive and rational model for GaN heteroepitaxy along polar, nonpolar and semipolar orientations, and is broadly extensible to the heteroepitaxy of other materials. We demonstrate furthermore that the control of morphological evolution, based on invoking a detailed knowledge of the v-plots, holds a key to the reduction of microstructural defects through effective bending of dislocations and blocking of stacking faults. The status and outlook of semipolar and nonpolar GaN growth on sapphire substrates will be presented.

• Open/close Growth of 2 inch ZnO bulk single crystal by the hydrothermal method

  Katsumi Maeda et al 2005 Semicond. Sci. Technol. 20 S49 Tag this article

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  Zinc oxide (ZnO) single crystals were grown by the hydrothermal method using a platinum inner container. The 2 inch ZnO wafers obtained from these bulk crystals possess an extremely high crystallinity and purity. The electrical resistivity is highly uniform over the entire wafer area. After annealing, the step-and-terrace structure was observed on the surface of the wafer. The etch pit density was decreased to less than 80 cm ⁻². These results suggest that these 2 inch ZnO wafers are suitable for wide band gap device applications.