Effects of Post-annealing on the Passivation Interface Characteristics of AlGaN/GaN High Electron Mobility Transistors PDF Download
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Languages : en
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Author: Minh-Trang Teresa Ha
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Category :
Languages : en
Pages : 43
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AlGaN/GaN HEMTs are the most promising high power switching devices. The material properties of III-nitrides are exceptionally better than that of Si and GaAs. GaN-based devices have been recorded to have higher operating temperatures and higher breakdown field due to the wide bandgap. AlGaN/GaN heterostructures forms 2DEG without doping due to the spontaneous polarization. The performance and reliability of AlGaN/GaN HEMTs are dependent on the structure of the AlGaN/GaN heterostructures. Surface passivation has been proven to improve the 2DEG conductivity and device performance. 20 nm of plasma-enhanced chemical vapor deposition (PECVD) SiN was deposited on AlGaN/GaN HEMTs, and the PECVD SiN passivated sample demonstrated higher carrier concentration of 9.88 ? 1012 cm-2 compared to the un-passivated sample, 8.08 ? 1012 cm-2. High temperature annealing is an important processing step in the fabrication of the devices, and the effects have shown to improve the DC and RF performance. High temperature annealing may affect the structure and the 2DEG conductivity. The annealing effects modifies the AlGaN layer and the AlGaN/GaN interface. Herein, we present the a study on the thermal stability of the PECVD SiN passivation layer on AlGaN/GaN HEMT structures at high temperature anneals. High-resolution x-ray diffraction (HRXRD) measurements were used to investigate the strain of AlGaN layer, and Hall measurements were used to investigate the 2DEG conductivity. PECVD SiN passivated and un-passivated AGaN/GaN HEMTs structure underwent high temperature thermal anneals for 30 minutes in N2. The starting temperature of the annealing is 400?C with step of 50?C until degradation. Degradation was determined through Hall sheet resistivity and mobility measurements. The ending annealed temperature is 1000 ?C and 700 ?C for passivated and control samples, respectively. From no anneal to degradation temperature, the 2DEG conductivity dropped by 15% and 34% for passivated and un-passivated samples, respectively. The HRXRD measurements found the change in-plane strain of the AlGaN layer after high temperature anneals. Higher in-plane strain showed higher 2DEG conductivity. In-plane strain from no anneal to degradation temperature dropped from 2% and 7% for passivated and un-passivated samples, respectively. Therefore, the passivated sample demonstrated to be more stable at high temperatures. The SiN passivation layer adds tensile stress to the AlGaN layer thus increased the piezoelectric effect and 2DEG conductivity.
Author: Sameer Jayanta Joglekar
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Category :
Languages : en
Pages : 161
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Gallium Nitride (GaN) belongs to a class of materials called wide band-gap semiconductors. In recent years, the versatile nature of this material has been exploited for a wide range of applications from solid state lighting to RF and microwave communication, as well as high power switching. The first part of this thesis discusses planar AlGaN/GaN transistors. GaN is a piezoelectric material, and changes in mechanical stress result in a change in the charge density which in turn affects the maximum current in AlGaN/GaN transistors. Finite element modelling techniques were applied to quantify the mechanical stress distribution in planar AlGaN/GaN RF transistors resulting from device fabrication, and operation in the on- and off-state. Thereafter, two important surface and interface effects were studied in this thesis. In the first one, the impact of surface cleanings, surface treatments and plasma-based dry etch conditions on two different types of ohmic contact technologies was investigated. Contact resistance measurements were correlated with surface characterization results. The second was that of interface positive charges at the Al2O3-GaN interface and the increase in electron density in the device resulting from them. In both these problems, a combination of device electrical measurements and material characterization techniques was used to establish direct correlations between device behavior and material properties. The second part of the thesis deals exclusively with nano-ribbon (NR) or fin-like AlGaN/GaN transistors. Fundamental transport properties of charge density and mobility in NR devices were studied in order to understand the difference in behavior of these devices from planar devices. The influence of passivation films on the charge density in these structures was investigated, using Al2O3 passivation as a specific example. Electron mobility degradation due to sidewall-scattering in NR devices was quantified using different mobility extraction methods based on device measurements. The thesis concludes with a potential application of NR AlGaN/GaN transistors for high linearity power amplification. A new kind of transistor with varying threshold voltages along the gate width is proposed to improve the DC and RF linearity of GaN-based devices.
Author: Michael Hosch
Publisher: Cuvillier Verlag
ISBN: 3736938446
Category : Technology & Engineering
Languages : en
Pages : 129
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This thesis deals with the analysis and optimization of some of the most prominent non-ideal effects in AlGaN/GaN high electron mobility transistors used in microwave applications as well as the optimization of the RF gain. The effect of current collapse, the root cause of leakage currents as well as field-dependent self-heating effects have been investigated by eletrical characterization using well established techniques and have been analyzed using 2-dimensional physical device simulations. It will be shown that the origin of all effects is strongly related to the device surface and some are even competing effects making device optimization a challenge. However, a detailed localization of the regions affecting device performance will be given leading to a better understanding for fabrication process optimization. Finally, I simulation study is conducted giving suggestions for RF gain improvement based on very simple device layout variations.
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Languages : en
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Here we studied the effect of buffer layer quality on dc characteristics of AlGaN/GaN high electron mobility (HEMTs). AlGaN/GaN HEMT structures with 2 and 5 [mu]m GaN buffer layers on sapphire substrates from two different vendors with the same Al concentration of AlGaN were used. The defect densities of HEMT structures with 2 and 5 [mu]m GaN buffer layer were 7 × 109 and 5 × 108 cm2, respectively, as measured by transmission electron microscopy. There was little difference in drain saturation current or in transfer characteristics in HEMTs on these two types of buffer. However, there was no dispersion observed on the nonpassivated HEMTs with 5 [mu]m GaN buffer layer for gate-lag pulsed measurement at 100 kHz, which was in sharp contrast to the 71% drain current reduction for the HEMT with 2 [mu]m GaN buffer layer.
Author: Jaesun Lee
Publisher:
ISBN:
Category : Heterostructures
Languages : en
Pages : 176
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Abstract: AlGaN/GaN high electron mobility transistors (HEMTs) have demonstrated high current levels, high breakdown voltages, and high frequency power performance due to its unique material properties. The further improvements of AlGaN/GaN HEMTs rely on the improvement of material quality and further reduction of parasitic resistance. The purpose of this study is to fabricate and characterize AlGaN/GaN HEMTs for high frequency and high power applications. The first focus of this research is to investigate the post-gate annealing effect on the direct current and radio frequency device performances. Post-gate annealing of AlGaN/GaN turns out to be one of the simple and effective techniques to improve breakdown voltage and power performance of devices dramatically. Especially, after post-annealing at 400 0C for 10 minutes, the maximum drain current at a gate bias of 1 V increases from 823 mA/mm to 956 mA/mm. The transconductance of the devices was improved from 223 mS/mm to 233 mS/mm. The breakdown voltages of the devices were enhanced remarkably from 25 V to 187 V. The threshold voltage exhibited a negative shift. The values fT and fMAX increase from 24 GHz and 80 GHz to 55 GHz and 150 GHz, respectively. The output power and associated gain at 10 GHz are improved from 16.4 dBm and 11.4 dB to 25.9 dBm and 19 dB, respectively. The power added efficiency (PAE) is improved from 29.4 to 52.5 %. The second focus is to develop self-aligned AlGaN/GaN HEMTs, which are very attractive because of the minimized source access resistance. However, the thick metal scheme and high processing temperature of ohmic contacts on III-nitrides hinder the realization of self-aligned devices. In this study, self-aligned AlGaN/GaN high electron mobility transistors are fabricated and characterized with the thin metal schemes of Ti/Al/Ti/Au and Mo/Al/Mo/Au for gate to source and drain self-alignment. Thin Mo/Al/Mo/Au metal layer show good ohmic contact behavior even after annealed for 5 minutes at 600 0C in a furnace while thin ohmic metal scheme of Ti/Al/Ti/Au does not produce ohmic contact even after annealed at 750 0C for 30 minutes. The third focus is to develop the enhancement mode AlGaN/GaN HEMTs. Quasi-enhancement mode AlGaN/GaN HEMT devices with 1-um gate length are fabricated. These quasi-enhancement mode devices exhibit the threshold voltage of as low as - 0.3 V, a gm of 140 mS/mm, an fT of 4.3 GHz, and an fMAX of 13.3 GHz, respectively. Further improvement of enhancement-mode GaN-based HEMT devices is desired for applications of complementary integrated circuits.
Author: David J. Meyer
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Trupti Ranjan Lenka
Publisher: Springer Nature
ISBN: 9811921652
Category : Technology & Engineering
Languages : en
Pages : 246
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This book covers two broad domains: state-of-the-art research in GaN HEMT and Ga2O3 HEMT. Each technology covers materials system, band engineering, modeling and simulations, fabrication techniques, and emerging applications. The book presents basic operation principles of HEMT, types of HEMT structures, and semiconductor device physics to understand the device behavior. The book presents numerical modeling of the device and TCAD simulations for high-frequency and high-power applications. The chapters include device characteristics of HEMT including 2DEG density, Id-Vgs, Id-Vds, transconductance, linearity, and C-V. The book emphasizes the state-of-the-art fabrication techniques of HEMT and circuit design for various applications in low noise amplifier, oscillator, power electronics, and biosensor applications. The book focuses on HEMT applications to meet the ever-increasing demands of the industry, innovation in terms of materials, design, modeling, simulation, processes, and circuits. The book will be primarily helpful to undergraduate/postgraduate, researchers, and practitioners in their research.
Author: Michael James Murphy
Publisher:
ISBN:
Category :
Languages : en
Pages : 226
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Author: Hongyu Yu
Publisher: CRC Press
ISBN: 1351767607
Category : Science
Languages : en
Pages : 301
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GaN is considered the most promising material candidate in next-generation power device applications, owing to its unique material properties, for example, bandgap, high breakdown field, and high electron mobility. Therefore, GaN power device technologies are listed as the top priority to be developed in many countries, including the United States, the European Union, Japan, and China. This book presents a comprehensive overview of GaN power device technologies, for example, material growth, property analysis, device structure design, fabrication process, reliability, failure analysis, and packaging. It provides useful information to both students and researchers in academic and related industries working on GaN power devices. GaN wafer growth technology is from Enkris Semiconductor, currently one of the leading players in commercial GaN wafers. Chapters 3 and 7, on the GaN transistor fabrication process and GaN vertical power devices, are edited by Dr. Zhihong Liu, who has been working on GaN devices for more than ten years. Chapters 2 and 5, on the characteristics of polarization effects and the original demonstration of AlGaN/GaN heterojunction field-effect transistors, are written by researchers from Southwest Jiaotong University. Chapters 6, 8, and 9, on surface passivation, reliability, and package technologies, are edited by a group of researchers from the Southern University of Science and Technology of China.
