H. Hung

Nitride-based LEDs with p-InGaN capping layer

Nitride-based light-emitting diodes (LEDs) with Mg-doped In/sub 0.23/Ga/sub 0.77/N capping layers were successfully fabricated. Compared to Mg-doped GaN layers, it was found that we could achieve a much larger hole concentration from Mg-doped In/sub 0.23/Ga/sub 0.77/N layers. It was also found that we could reduce the 20 mA operation voltage from 3.78 to 3.37 V by introducing a 5-nm-thick In/sub 0.23/Ga/sub 0.77/N layer on top of the p-GaN layer. Furthermore, it was found that output intensity of LEDs with In/sub 0.23/Ga/sub 0.77/N capping layer was much larger, particularly at elevated temperatures.

Vertical single-crystal ZnO nanowires grown on ZnO:Ga/glass templates

Vertical single-crystal ZnO nanowires with uniform diameter and uniform length were selectively grown on ZnO:Ga/glass templates at 600/spl deg/C by a self-catalyzed vapor-liquid-solid process without any metal catalyst. It was found that the ZnO nanowires are grown preferred oriented in the [002] direction with a small X-ray diffraction full-width half-maximum. Photoluminescence, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy measurements also confirmed good crystal quality of our ZnO nanowires. Field emitters using these ZnO nanowires were also fabricated. It was found that threshold field of the fabricated field emitters was 14 V//spl mu/m. With an applied electric field of 24 V//spl mu/m, it was found that the emission current density was around 0.1 mA/cm/sup 2/.

Well-Aligned, Vertically Al-Doped ZnO Nanowires Synthesized on ZnO : Ga ∕ Glass Templates

High-density, single-crystal, vertically aligned, Al-doped ZnO nanowires with an Al content of 1.05 atom % were synthesized on ZnO:Ga/glass templates at 550°C. Although introducing Al did not change the physical dimensions of the ZnO nanowires, the lattice constant increased by 0.25% and the optical properties of the ZnO nanowires were degraded. However, the experimental results also showed that the threshold emission field can be significantly decreased from 16 to 10 V/μm, and the work function, Φ, can also be reduced from 5.3 to 3.39 eV by introducing Al atoms into the ZnO nanowires.

Terahertz temperature-dependent defect mode in a semiconductor-dielectric photonic crystal

In this work, terahertz (THz) temperature-dependent properties of defect mode in a defective semiconductor-dielectric photonic crystal (SDPC) are theoretically investigated based on the calculated transmittance spectrum. Two different defective PCs, the symmetric structure of (Si/SiO2)NInSb(SiO2/Si)N and the asymmetric one of (Si/SiO2)NInSb(Si/SiO2)N, will be considered. With a strongly temperature-dependent permittivity in defect layer InSb, the defect mode can be thermally tuned, that is, the defect frequency will be shifted to higher frequency as the temperature increases. With the inherent loss in InSb, the strength of defect mode will be strongly depressed at a higher temperature. We use the condition of impedance match to explain the presence of defect mode. The understanding of properties of defect mode could be of technical use in the terahertz optoelectronic applications.

ANALYSIS OF TUNABLE MULTIPLE-FILTERING PROPERTY IN A PHOTONIC CRYSTAL CONTAINING STRONGLY EXTRINSIC SEMICONDUCTOR

In this work, we analyze the tunable multiple-filtering property at infrared frequency in a finite semiconductor-dielectric photonic crystal (SDPC), (AB) P A, where A is a strongly extrinsic semiconductor, n-type germanium (n-Ge). B is a dielectric material, and P is the number of periods. It is found that multiple filtering phenomenon can be obtained in the region where the permittivity of n-Ge is negative. The number of resonant peaks is found to be equal to P. With the permittivity of n-Ge being concentration-dependent, these resonant peaks can be shifted as a function of impurity concentration. The analysis indicates that such an SDPC can work as a tunable multichannel filter which is of technical use for the semiconductor applications in optical communications.

ENHANCEMENT OF NEAR-INFRARED PHOTONIC BAND GAP IN A DOPED SEMICONDUCTOR PHOTONIC CRYSTAL

In this work, the enhancement in photonic band gap (PBG) in a dielectric-semiconductor photonic crystal (DS PC) is investigated. We consider two possible schemes that can be used to enhance the PBG in the near-infrared region. The flrst scheme is to add an ultrathin metal layer into the DS PC such that a structure of ternary metal-dielectric-semiconductor (MDS) PC is formed. The second scheme is to make use of the heterostructured PC. In scheme 1, it is found that the addition of metal layer will signiflcantly move the left band edge to the shorter wavelength position, leading to an enlargement in the PBG. This enlargement can be extended as the thickness of metal fllm is increased. In addition, a pronounced enhancement in PBG is achieved when the metal with a higher plasma frequency is used. In scheme 2, we flnd that the PBG can be signiflcantly enlarged compared to scheme 1. In addition, the increase in the band extension is shown to be four times larger than that in scheme 1. The results illustrate that, in order to enhance the PBG, the use of scheme 2 is superior to scheme 1. The enhancement of near- infrared (NIR) PBG is of technical use in the optical communications.

Selective growth of vertical ZnO nanowires on ZnO:Ga∕Si3N4∕SiO2∕Si templates

High density vertical single crystal ZnO nanowires were selectively grown on ZnO:Ga∕Si3N4∕SiO2∕Si templates at various temperatures by a two-step oxygen injection process of self-catalyzed vapor-liquid-solid (VLS) technology. It was found that tips of the ZnO nanowires are hexagonal. It was also found that average length of the ZnO nanowires increased while the average tip diameter of the ZnO nanowires decreased as the growth temperature increased. Furthermore, it was found that the ZnO nanowires grown at 500°C were “tube-shaped” while the ZnO nanowires grown at 700°C were “cone-shaped.” Photoluminescence (PL), x-ray diffraction (XRD), and energy depersive x-ray (EDX) results all indicate that the quality of our ZnO nanowires is good.

Magnetooptical Effects in Wave Properties for a Semiconductor Photonic Crystal at Near-Infrared

We investigate the magnetooptical effects in near-infrared wave properties for a semiconductor-based photonic crystal (PC) containing n-type InSb. We find that the static magnetic field serves as an externally switching and tuning agent in the wave transmission near 1.54 μm. With the applied static magnetic field, an additional small transmission gap, which does not appear in the absence of static magnetic field, can be opened up. The position of this gap can also be further tuned by the variation in this static field. The analytical results near this wavelength reveal that such a semiconductor PC can work as a magnetically tunable notch filter, which will be informative and of technical use to signal processing in optical communications.

Tunable Multichannel Filter in a Photonic Crystal Containing Semiconductor Photonic Quantum Well

A tunable multichannel filter in the finite photonic crystal (PC) containing photonic quantum well (PQW) as a defect is proposed. The symmetric structure (AB)<i>P</i>(CD)<i>Q</i>( BA)<i>P</i> and the asymmetric structure (AB)<i>P</i>(CD)<i>Q</i>(AB)<i>P</i> are considered in this work. Here, the host PC of (AB)<i>P</i> is made of Si for layer A and of SiO₂ for layer B. In the PQW, (CD)<i>Q</i>, C also is Si, but D is an extrinsic semiconductor, <i>n</i>-type silicon (<i>n</i>-Si). With the use of <i>n</i>-Si, it is found that both structures can function as a tunable multichannel filter in the infrared region. The number of channels is equal to <i>Q</i> + 1 in the symmetric structure, whereas it is <i>Q</i> for the asymmetric one. The positions of multiple resonant peaks can be tuned by the variation in the impurity concentration of <i>n</i> -Si. The proposed filter could be used to design the wavelength division multiplexer filter that is of technical use in optical communications.

High temperature characteristics of ZnO-based MOS-FETs with photochemical vapor deposition SiO 2 gate oxide

ZnO-based MOSFETs were fabricated in this study. The I-V curve of the source-drain ohmic contacts shows in figure 1. We can get the good ohmic performance by using the Ti/Al/Ti/Au metals and annealing at 525 °C, 3 minutes. Then, we deposited the SiO2 layer by using photo-CVD system and the schematic diagram of photo-CVD system shows in figure 2.