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Advanced Semiconductor Devices & Microsystems (ASDAM), 2012 Ninth International Conference on

Date 11-15 Nov. 2012

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Displaying Results 1 - 25 of 81
  • [Title page]

    Publication Year: 2012 , Page(s): c1
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  • [Copyright notice]

    Publication Year: 2012 , Page(s): i - iv
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  • Contents

    Publication Year: 2012 , Page(s): v - x
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  • Preface

    Publication Year: 2012 , Page(s): xi
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  • GaN-based electronics

    Publication Year: 2012 , Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB) |  | HTML iconHTML  

    An overview of III-nitride heterojunction FET technologies is given in this paper. Structural parameter designs of HEMTs, including various field-plate parameters, are described for high-voltage applications. For low-leakage operation, future HEMT technology on a free-standing GaN substrate is presented. Some of the theoretical design issues will be also addressed. View full abstract»

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  • Early stage degradation of InAlN/GaN HEMTs during electrical stress

    Publication Year: 2012 , Page(s): 7 - 10
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    Early stage degradation of InAlN/GaN HEMTs submitted to OFF and semi-ON state stress at a drain bias of 50 V was investigated. Degradation in different parts of the device upon OFF and semi-ON state stress inferred from the comprehensive electrical characterization indicates predominantly an hot-electron degradation mechanism, as no degradation in the gate leakage current was observed for both stress conditions. Based on `end' resistance measurements suggesting more pronounced degradation in the drain and source resistance after OFF and semi-ON state stressing, respectively, it is speculated that impact ionization can play a role in the degradation of InAlN/GaN HEMTs. View full abstract»

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  • TCAD modelling of current dispersion in a 0.25 µm gate length GaN HEMT

    Publication Year: 2012 , Page(s): 11 - 14
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (365 KB) |  | HTML iconHTML  

    Current dispersion due to acceptor-type defects acting as electron traps are studied using 2D TCAD transient simulations. High and low drain pulse voltages are applied to study a dynamic picture of trapping and de-trapping of electrons using Drift Diffusion and Hydrodynamic transport models. In addition, Schottky electron tunnelling is employed to transient simulations in the presence of different densities of traps in the barrier to investigate how tunnelling affects the drain current at off-state. View full abstract»

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  • Investigation of robust bandgap semiconductor structures using optical spectroscopy methods

    Publication Year: 2012 , Page(s): 15 - 18
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (191 KB) |  | HTML iconHTML  

    In the paper we show and discuss the utilization of different optical spectroscopy methods such as photoluminescence or μ-Raman microscopy with UV or VIS excitation to analysis of robust bandgap materials properties particularly GaN and ZnO based structures. These techniques are capable to discover tiny changes in material properties induced by variety of influences such as material composition, doping, strain or temperature. The measurements of Raman spectra of annealed ZnO/GaP at different temperatures revealed that the structure annealed at 340°C show considerable changes in Raman spectra due to re-crystallization. The calibration measurements of Raman and PL temperature shift were done for AlGaN/GaN high electron mobility transistor (HEMT) structure with the aim to investigate the temperature distribution inside the HEMTs channel. View full abstract»

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  • Conductive metal oxide based gates for self-aligned technology of AlGaN/GaN HEMTs

    Publication Year: 2012 , Page(s): 19 - 22
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (186 KB) |  | HTML iconHTML  

    We present advanced gate interface of AlGaN/GaN HEMTs for self-aligned gate processing technology. The in-diffusion of the gate metal components to the AlGaN barrier layer can be eliminated. It can be done by inserting thin conductive metal oxide layer on the interface between the metal and the wide bandgap semiconductor layer. The proposed gate electrodes are prepared by thermal oxidation of high work function metals as Ni or Ir (RTA in pure O2 ambient at T=800 °C for 1 min). The highest value of oxidation temperature is limited by the optimal temperature of the ohmic contact formation. It is shown that high temperature formation of IrO2 and NiO gate contact layers has no significant impact on transport parameters of 2DEG channel of AlGaN/GaN HEMT structures thus it could be applied in self-aligned gate processing technology of the device. View full abstract»

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  • Gates of AlGaN/GaN HEMT for high temperature gas sensing applications

    Publication Year: 2012 , Page(s): 23 - 26
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    The sensing capability of the Pt or Ir based Schottky gate electrodes on AlGaN/GaN heterostructures at elevated temperatures can be improved. It is carried by inserting a thin interlayer of conductive metal oxide between the sensing electrode and the semiconductor barrier layer. High temperature sensing ability of new composite gates is evaluated by detection of hydrogen. We investigate the different absorbing layers and the influence of composition and interfacial oxide layer thickness on sensitivity and response time of gas sensors. View full abstract»

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  • High temperature AlGaN/GaN HFET microwave characterization

    Publication Year: 2012 , Page(s): 27 - 30
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (365 KB) |  | HTML iconHTML  

    The paper reports high temperature on-wafer microwave characterization setup for AlGaN/GaN HEMT devices. DC output characteristics as well as microwave parameters fT and fmax were measured and visualized in the form of 3-D diagrams in the temperature range from room temperature up to 425°C. Significant influence of temperature on DC and microwave properties was observed. View full abstract»

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  • Characterization and control of insulated gates for GaN power switching transistors

    Publication Year: 2012 , Page(s): 31 - 36
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (993 KB) |  | HTML iconHTML  

    We observed the peculiar capacitance-voltage (C-V) characteristics with two capacitance steps in the Al2O3/AlGaN/GaN samples prepared by atomic layer deposition where the interface states near the midgap or deeper in energies act as fixed charges. From the voltage shift at the reverse bias in the photo-assisted C-V curve, we estimated the interface state density distribution at the Al2O3 /AlGaN interface for the first time. The effects of the inductively coupled plasma (ICP) etching of AlGaN on the interface properties of the Al2O3/AlGaN/GaN structures were investigated. The transmission electron microscopy and X-ray photoelectron spectroscopy analyses indicated that monolayer-level roughness and disorder of the chemical bonds at the AlGaN surface caused poor C-V characteristics due to high-density interface states at the Al2O3/ICP-etched AGaN interface. View full abstract»

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  • Current instabilities and other reliability aspects in AlGaN/GaN MOS-HFETs with atomic layer deposited Al2O3 as gate oxide

    Publication Year: 2012 , Page(s): 37 - 40
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    An impact of the different voltage ramps (from 25mV/s to 20V/s) in off-state regime for HFET and MOS-HFET was experimentally investigated. Because of the temperature in the channel drops at low voltage steps, density of temperature-active interface states and states in the GaN buffer near the channel is reduced, and therefore the IDS,off-state decreases. A positive temperature coeficient is attended. An another behaviour for MOS-HFET for fast traps in comparison to HFET was observed. A smaller temperature-dependence of fast traps in comparison to slow traps can be responsible for this effect. The same tendency of IDS,off.state for all devices were found. The MOSHFET exhibited no change of drain current IDS,off-state for 5 hours, but for the HFET the value was more than 500 times higher. View full abstract»

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  • Influence of layer structure on electrical properties of AlGaN/GaN HEMTs

    Publication Year: 2012 , Page(s): 41 - 44
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB) |  | HTML iconHTML  

    The C-V and I-V characteristics of the Ni/Al0.26Ga0.74N/GaN and Ni/Al0.20Ga0.80N/GaN Schottky diodes were measured for determination of structures electrical parameters as well as influence of metal-pad electrode to Schottky barrier height evaluation. From measured C-V curves, the sheet charge density of carriers in the channel was determined. The I-V characteristics were measured in the temperature range from 298 to 473 K and analyzed considering different current-transport mechanisms. The Schottky barrier height of both investigated structures with metal-pad show equal value ~1.3 eV at 298 K, while for structures without metal-pad the barrier height of the Schottky diodes was 2.23 eV and 2.02 eV for Ni/Al0.26Ga0.74N/GaN and Ni/Al0.20Gain0.80N/GaN sample, respectively. This results indicate the presence of excess oxide layer under Schottky contact at AlGaN surface during the contact processing. View full abstract»

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  • Material and device issues of InAlN/GaN heterostructures

    Publication Year: 2012 , Page(s): 45 - 50
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (209 KB) |  | HTML iconHTML  

    Motivation for replacing the AlGaN barrier layer of the conventional AlGaN/GaN HEMTs with lattice-matched InAlN is explained. State-of-the-art InAlN/GaN HEMTs are reviewed; emphasize is given to the analysis of the normally-off InAlN/GaN HEMTs using either a gate recessing or a concept of polarization engineering. Reliability issues of InAlN/GaN HEMTs are studied for different stress conditions and results discussed in respect to AlGaN/GaN HEMTs. Concept of InAlN/GaN/AlGaN double-heterostructure QW HEMT is shown to be more effective in blocking the hot electron injection in to the buffer. Novel InN-channel based devices are suggested with a relaxed InAlN buffer. The InN/InAlN-based HEMTs should be the choice for reaching a THz frequency range. View full abstract»

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  • Electrical characterization of the InAlN/GaN heterostructures by capacitance methods

    Publication Year: 2012 , Page(s): 51 - 54
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (186 KB) |  | HTML iconHTML  

    This paper highlights the electrical characterization of 4 types of the Schottky structures prepared on InAlN/GaN epi-layer designed for HEMT's with the AlN buffer layer and semi-insulating 6H-SiC substrate, which have different mechanical strain due to different growth conditions, using capacitance-voltage and Deep Level Transient Spectroscopy methods (DLTS). The sudden fall of capacitance in the range of reverse voltage from -2.5 to -3.3 V is caused by heterostructure's interface depletion. According to the DLTS measurement it is highly probable that the similar system of defects is present in all samples. Parameters of 7 hole-like traps were identified. Three of them HT1 (1.48 eV) HT2 (1.06 eV) and HT4 (1.01 eV) are certainly present in two structures and one HT3 (1.24 eV) in three structure. The highest concentration of defects has structure with the highest mechanical strain (Strain Raman 2 GPa). View full abstract»

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  • Electrothermal analysis of In0.12Al0.88N/GaN HEMTs

    Publication Year: 2012 , Page(s): 55 - 58
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (421 KB) |  | HTML iconHTML  

    InAlN/GaN High Electron Mobility Transistors (HEMTs) are very popular because of their promising electrical and thermal properties. With the innovation of these structures and the development of fabrication processes, there are still many serious issues like current collapse or self-heating effects, which must be addressed. In this work, the DC device behavior is studied both experimentally and by means of two-dimensional hydrodynamic device simulations. Very good agreement between measurements and simulations with Minimos-NT is achieved using the hydrodynamic transport model including self-heating and impact ionization effects. View full abstract»

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  • Interface traps in insulator/AlGaN/GaN heterostructure capacitors

    Publication Year: 2012 , Page(s): 59 - 62
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (145 KB) |  | HTML iconHTML  

    We have modeled and simulated capacitance voltage characteristics of metal/insulator/semiconductor heterostructure capacitor. The heterostructure was formed by AlGaN/GaN. Two types of distributions of interface traps in the AlGaN energy gap were used in our calculations and the two types of interface traps were assumed to be present at the insulator/AlGaN interface - an acceptor type and a donor type traps. The first one is obviously obtained in the upper part of the energy gap and the second one in the lower part of the gap. We obtained C-V characteristics with two capacitance steps which are sometimes obtained in experimental practice. The behavior and a shape of the C-V curves have been analyzed. The two steps in the characteristics correspond to the AlGaN and the GaN layers depletion. We observed also the stretching of the C-V curves as a result of interface traps presence in the structure. View full abstract»

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  • Arsenide-based terahertz materials and devices for 800 and 1550 nm excitations

    Publication Year: 2012 , Page(s): 63 - 70
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (660 KB) |  | HTML iconHTML  

    Photoconductors based on III-V semiconductor compounds, and suitable for 800 and 1550 nm excitations, were grown using the low temperature growth technique in a Molecular Beam Epitaxy (MBE) system. Photoconductive antennas were fabricated and tested in a time-domain spectroscopy (TDS) system. The photoconductors were synthesised to absorb light at the wavelengths of 800 nm or 1.55 μm. The photoconductive antennas were composed of aperture and dipole structures. A combination of the unique material characteristics, such as femtosecond carrier lifetime, high dark resistivity and high mobility, and the geometry of the antenna structures resulted in the development of fully operational THz devices at both excitation wavelengths. View full abstract»

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  • GaAs nanowhiskers for femtosecond photodetectors and THz emitters

    Publication Year: 2012 , Page(s): 71 - 74
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    We have developed and characterized ultrafast and highly sensitive photodetectors based on GaAs nanowhiskers fabricated with an improved top-down etching method. We evaluated the material properties of the etched nanowhiskers by micro photoluminescence measurements and studied the effect of post annealing on nanowhiskers' luminescence. The nanowhiskers were integrated into the coplanar striplines for device testing using DC and time-resolved electro-optic characterization techniques. Our photodetectors exhibit a very low dark current below 500 pA at 10 V bias as well as a high responsivity of 0.19 A/W at 30 V, and a cut-off frequency of 1.3 THz. These characteristics make the GaAs nanowhisker photodetectors very promising candidates for high-speed optoelectronics and efficient THz emitters. View full abstract»

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  • Improving output power of terahertz heterodyne photomixer by impedance matching

    Publication Year: 2012 , Page(s): 75 - 78
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB) |  | HTML iconHTML  

    This work explores the possibilities of directly addressing the impedance mismatch problem in the design and modelling of a continuous wave photomixer employing high impedance antennas, based on conservative design rules and material choices. Two antenna designs derived from the folded dipole are presented and compared to published results from an existing device showing an improvement of up to 4.6 dB in output power. The possibilities of implementing a lumped element matching network are discussed. View full abstract»

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  • Cathodoluminescence characterization of InGaN/GaN QW pyramidal structure by Monte Carlo method

    Publication Year: 2012 , Page(s): 79 - 82
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (239 KB) |  | HTML iconHTML  

    The aim of this paper is to present the quantitative study of cathodoluminescence from InGaN/GaN single quantum wells grown on the GaN pyramid facets. Monte Carlo method has been used to investigate the generation, diffusion and recombination of minority carriers inside the structure under focused electron beam. The influence of various carrier diffusion lengths in top GaN layer and buffer GaN on the depth distributions of recombination and the contribution of individual layers to the cathodoluminescence in dependence on the thickness of the top GaN layer have been determined. The possibility to determine the position of the quantum well within the structure using cathodoluminescence analysis has been discussed. View full abstract»

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  • Nanostructures for plasmonic solar cells and biosensing

    Publication Year: 2012 , Page(s): 83 - 86
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (402 KB) |  | HTML iconHTML  

    The key element for real-life plasmonics application depends on the fabrication of subwavelength nanostructures supporting localized surface plasmon resonance (LSPR) with mass reproducibility yet low cost. We have investigated two fabrication techniques for photovoltaic and biosensing purposes, i.e. self-assembly nanoisland and nanosphere lithography, which enable formation of relatively large area LSPR supporting arrays on transparent substrates yet without demanding for expensive manufacturing equipments. View full abstract»

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  • Nucleation and annihilation of magnetic vortices in Pacman-like nanodots observed by micro-Hall probes

    Publication Year: 2012 , Page(s): 87 - 90
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (356 KB) |  | HTML iconHTML  

    We have used micro-Hall probe for the study of vortex dynamics in micromagnetic objects with lowered symmetry. The Pacman-like nanodot of the diameter of 1 μm was placed directly on the Hall probe and the signal was red in band resistance configuration. We show that the vortex nucleation and annihilation, as well as s-and c-state creation/annihilation are clearly visible on the magnetization reversal characteristics at 77 K. The experimental characteristics is in good agreement with the one calculated by micromagnetic simulations. View full abstract»

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  • Detection elements for on-cantilever laboratory

    Publication Year: 2012 , Page(s): 91 - 94
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (329 KB) |  | HTML iconHTML  

    Micrometer-scaled cantilever-based sensors can be utilized in electrostatic and magnetic measurements and also are perspective for future chemical and biological sensing applications. GaAs is the most used III-V material for cantilever probe development thanks to its optoelectronic properties, high mobility 2D electrons, high piezoresistivity and sufficient mechanical properties. Novel sensing probes, prepared by integration of various detection elements are perspective for specific requirements. This work is mainly focused on technology process of such micro-CLs and also on fabrication of detection elements (transistors) with the aim to integrate directly on the micro-CLs. View full abstract»

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