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Optoelectronic and Microelectronic Materials and Devices, 2008. COMMAD 2008. Conference on

Date July 28 2008-Aug. 1 2008

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  • Table of contents

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  • Author index

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  • Abstract cards

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    Presents abstracts for the articles comprising the conference proceedings. View full abstract»

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  • Book of abstracts

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    Summary form only given. Provides an abstract for each of the seven keynote presentations and a brief professional biography of each presenter. View full abstract»

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  • Preface

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  • Alternating current bias-assisted photoenhanced oxidation of n-GaN in dionized water

    Page(s): 1 - 3
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    Patterned oxidation of n-GaN in water at room temperature is achieved by using an imprint technique and an alternating current (ac) bias-assisted photoelectrochemical process. Mold is fabricated by a double-side polished sapphire coated with indium tin oxide thin film to be an electrode for electric conduction and allow the high transparency for ultraviolet light. The growth rate of gallium oxide-based material of around 12 nm/min could be achieved when an ac bias of 3 V with a duty cycle of 90% was applied to the system. The film is determined by high-resolution transmission electron microscopy and selected area electron diffraction pattern. View full abstract»

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  • Improved robustness of AlGaN/GaN HEMTs using Deuterium to passivate the structural defects

    Page(s): 4 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1354 KB) |  | HTML iconHTML  

    GaN related devices have demonstrated excellent performances for high power, high temperature up to X-band applications. However, even if the reliability studies on AlGaN/GaN high electron mobility transistors (HEMT) have led to higher mean time to failure (MTTF), physical mechanisms induced by stresses are still not well known. This paper proposes an original solution to improve the robustness of the devices by passivating the traps that are supposed to be related to the degradation process. Based on the experience of previous works, we use Deuterium H+ to block the traps located at the AlGaN/GaN interface above the gated zone of the device, and the traps in the bulk of the conducting channel (2 dimensions electron gas : 2DEG). 2 batches of devices are processed with and without deuterium, and submitted to temperature stresses at 500degC. Low frequency noise (LFN) measurements are performed to track the evolution of the spectral current density of the drain current, which is known to be related to the structural evolution of the traps and of the crystal structure perfection. Devices with deuterium feature stable LFN spectra, while LFN spectra of the devices without deuterium evolve during the different stress steps. Thus, deuterium can offer an interesting alternative to enhance the robustness of AlGaN/GaN devices operating under stringent temperature conditions. View full abstract»

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  • Pulsed laser deposited stoichiometric ZnO thin films

    Page(s): 8 - 11
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    Room temperature free-exciton emission was observed in stoichiometric ZnO epilayers grown on Al2O3 substrates by pulsed laser deposition. Absorption and photoluminescence measurements clearly showed the free-exciton emissions at 3.30~3.31 eV. This free-exciton recombination results from the high-quality single-crystalline ZnO epilayers. Temperature-dependent excitonic properties revealed the higher thermal stability of stoichiometric ZnO epilayers with the effective phonon energy, electron-phonon interaction and exciton-phonon coupling of 65.2 meV, 0.093 meV/K and 680 meV, respectively. The strong exciton-phonon coupling has been attributed to the high Frohlich constant due to the strong localization energy in the stoichiometric ZnO epilayers. View full abstract»

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  • Experimental and numerical investigation of the electrical characteristics of vertical n-p junction diodes created by Si implantation into p-GaN

    Page(s): 12 - 15
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (161 KB) |  | HTML iconHTML  

    Vertical n-p junction diodes were fabricated by Si+ ion implantation into Mg doped p/p+ GaN, followed by rapid thermal annealing at 1260degC in NH3/N2 for 30 s. Implantations were performed at 40, 60 and 80 keV and circular contacts on the n-region were fabricated with various diameters between 100 and 600 mum. Light emission from the periphery of the contact under forward bias conditions confirmed the existence of an n-p junction. Current-voltage characteristics revealed rectifying behaviour associated with n-p junction. 2-Dimensional Sentaurus Devicetrade was used to simulate the device. Current density distribution indicates high current near the peripheral region and it appears that the performance of the device is not determined by the implantation conditions. Further optimisation of the vertical structure is required to improve the device performance. View full abstract»

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  • High resolution Deep Level Transient Spectroscopy of p-n diodes formed from p-type polycrystalline diamond on n-type silicon.

    Page(s): 16 - 19
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (89 KB) |  | HTML iconHTML  

    High resolution Laplace deep level transient spectroscopy (LDLTS) at temperatures up to 450 K has been applied to thin polycrystalline semiconducting diamond films deposited on n-type silicon. Such structures form p-n diodes and can be characterised by capacitance DLTS. The boron doped diamond films were grown by hot filament chemical vapour deposition and the diamond film thickness was 3-4 microns. The boron concentration in the diamond films ranged from 7times1018 cm-3 to 1times1019 cm-3. In the LDLTS an isothermal measurement of thousands of capacitance transients was made and then averaged, and the result was inverse transformed to find the trap emission rate. The temperature was chosen as the maximum of the conventional DLTS emission peak. Conventional DLTS showed a combination of majority and minority carrier emission from deep levels. Multiple peaks in the LDLTS spectra suggest that some of the defects are located in a strain field. Capture cross section measurements also show that these peaks exhibit a time dependent capture cross section, which is indicative of carriers being trapped at a large electrically active defect. It is shown in the paper that a combination of LDLTS and direct capture cross section measurements can be applied to semiconducting diamond and can be used to understand whether defects possess single or multiple energy levels, and whether the trapping is at an isolated point defect or in defects in the strain field of an extended defect. View full abstract»

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  • SIMS investigation of oxygen in 3C-SiC on Si

    Page(s): 20 - 22
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (185 KB) |  | HTML iconHTML  

    In this paper, we present and analyse secondary ion mass spectrometry (SIMS) measurements of oxygen concentration in 3C-SiC epitaxial layers on Si. The concentration of oxygen determined by SIMS was as high as 1019 to 1020 atom/cm3. Unlike silicon, oxygen can act as donor atoms in SiC with calculated ionization levels of 200 meV. It is generally believed that the main contribution of dopant concentration in the unintentionally doped SiC film is related to background nitrogen. Because of the high ionisation level, oxygen is not electrically active at room temperature. By measuring the conductivity of the films at higher temperatures, we extracted three donor energy levels: EA1 =79 meV, EA2 = 180 meV, and EA3 = 350 meV. The activation energy of 180 meV could be associated with the calculated ionization level for oxygen. Further analysis of the conductivity measurements at elevated temperatures will be performed to determine the electrically active donor concentration that is associated with the activation energy of 180 meV. View full abstract»

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  • Self-mixing displacement sensing using the junction voltage variation in a GaN laser

    Page(s): 23 - 25
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (245 KB) |  | HTML iconHTML  

    The self-mixing (SM) laser sensing technique allows a simple, self-aligned and robust system for measuring displacement. Low-cost blue emitting GaN laser diodes have recently become available due to the high volume requirements for Blu-ray disc devices such as high-definition video players and gaming consoles. These GaN lasers have a significantly shorter wavelength (around 405 nm) compared to other semiconductor lasers (generally around 800 nm for SM sensors). Therefore, if used in SM displacement sensors, they provide significantly higher resolution. Further to that, the measurement resolution is affected by the ability of the system to properly interpret the movement corresponding to the fraction of the half wavelength of the laser resulting in an incomplete fringe. Doubling the number of fringes will reduce the global error when a fringe is not properly detected. In this paper we report the world's first SM displacement measurement system based on junction voltage variation in blue emitting semiconductor lasers. Instead of monitoring the SM signals using a photo-diode, the signal is obtained via direct sensing of the laser junction voltage variation. This removes the need for a photo-diode, providing a cost reduction and increasing the reliability of the system. The sensitivity and precision of this system is evaluated and compared against the performance of systems using red (650 nm) and near IR (780 nm) laser based sensors with all three sensors sharing the same optical and electronic hardware. View full abstract»

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  • Isotropic dry-etching of SiC for AlGaN/GaN MEMS fabrication

    Page(s): 26 - 29
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    We present an isotropic fluorine based process to etch 4H-SiC substrates compatible with standard metallic etch masks and reasonable etching rates. Additionally, a new masking material has been established in order to obtain a stable protection of the layers underneath, based on a combination of sputtered AlN and Ni. The isotropic etching was achieved using a temperature assisted RF plasma etch process. The influence of gas flow, substrate temperature, RF power and working pressure on the etch rate and etch profile was analyzed. An optimized process with a lateral etch rate of 50 nm/min (RF power, working pressure, gas flow and temperature of 50 W, 0.4 mbar, 40 sccm SF6 and 425degC, respectively) was found, which enables the fabrication of novel resonant micro-electromechanical systems (MEMS) based on AlGaN/GaN heterostructures on SiC substrates. View full abstract»

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  • High resolution Laplace Deep Level Transient Spectroscopy studies of shallow and deep levels in n-GaN

    Page(s): 30 - 33
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (93 KB) |  | HTML iconHTML  

    Deep Level Transient Spectroscopy (DLTS) and high resolution Laplace DLTS (LDLTS) have been used to distinguish the difference between electrically active point and extended defects in MOVPE-grown n-type GaN. Three dominant features are observed in the conventional DLTS spectrum, with energies in the region of 40 meV, 550 meV and 1.46 eV. However, detailed examination with LDLTS shows that all these peaks consist of multiple emission rates. The low energy feature consists of three point defects closely spaced in energy, which are identified as ON, and SiGa. The feature at around 550 meV is shown to be due to defects in the strain field of a dislocation, which is deduced because the activation energy is dependent upon DLTS fill pulse length. LDLTS of this peak shows a very complicated spectrum, also indicative of a system of defects in a dislocation strain field. When applied to the very deep level of 1.46 eV, LDLTS shows multiple emission rates but they behave as point-defect like states. View full abstract»

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  • Suitability of synthetic diamond films for x-ray dosimetry applications

    Page(s): 34 - 37
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    Simple sandwich-type device structures have been fabricated by deposition of metal contacts on opposing faces of polycrystalline diamond films synthesised using chemical vapour deposition. The electrical characteristics of these devices have been investigated during exposure to a 6 megavolt photon beam from a clinical linear accelerator. The photocurrent appears to vary as the dose rate to the power of 0.78-0.85. The angular dependence of the photocurrent is less than 10 per cent. Further study on a range of CVD diamond substrates from different manufacturers is on-going. View full abstract»

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  • A study of the properties of RF sputtered MgXZn1-XO thin films

    Page(s): 38 - 40
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    MgXZn1-XO, a ZnO-based ternary compound, has been recognized as a promising material to be used in UV light emitting devices, UV laser diodes and UV detectors. In this paper, a batch of MgxZn1-xO films were fabricated using radio frequency sputtering on glass substrates with a Mg0.32Zn0.68O target. Then the structure and the optical properties of these films after being treated at different annealing temperatures were studied. View full abstract»

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