125,346 research outputs found
AlN/GaN-based MOS-HEMT technology: processing and device results
No full textProcess development of AlN/GaN MOS-HEMTs is presented, along with issues and problems concerning the fabrication processes. The developed technology uses thermally grown Al<sub>2</sub>O<sub>3</sub> as a gate dielectric and surface passivation for devices. Significant improvement in device performance was observed using the following techniques: (1) Ohmic contact optimisation using Al wet etch prior to Ohmic metal deposition and (2) mesa sidewall passivation. DC and RF performance of the fabricated devices will be presented and discussed in this paper
Dynamic Transconductance Dispersion Characterization of Channel Hot-Carrier Stressed 0.25<i>μ</i>m AlGaN/GaN HEMTs
No full textUsing the dynamic transconductance frequency dispersion technique, we characterize unstressed and hot-electron stressed short-channel AlGaN/GaN high-electron-mobility transistors. The results reported in this letter demonstrate that the stress-induced degradation in dc and pulsed characteristics is unlikely to be ascribable to sizable trap generation at the AlGaN/GaN interface
Coincident electron channeling and cathodoluminescence studies of threading dislocations in GaN
No full textWe combine two scanning electron microscopy techniques to investigate the influence of dislocations on the light emission from nitride semiconductors. Combining electron channeling contrast imaging and cathodoluminescence imaging enables both the structural and luminescence properties of a sample to be investigated without structural damage to the sample. The electron channeling contrast image is very sensitive to distortions of the crystal lattice, resulting in individual threading dislocations appearing as spots with black–white contrast. Dislocations giving rise to nonradiative recombination are observed as black spots in the cathodoluminescence image. Comparison of the images from exactly the same micron-scale region of a sample demonstrates a one-to-one correlation between the presence of single threading dislocations and resolved dark spots in the cathodoluminescence image. In addition, we have also obtained an atomic force microscopy image from the same region of the sample, which confirms that both pure edge dislocations and those with a screw component (i.e., screw and mixed dislocations) act as nonradiative recombination centers for the Si-doped c-plane GaN thin film investigated
Intentionally Carbon-Doped AlGaN/GaN HEMTs:Necessity for Vertical Leakage Paths
No full textDynamic ON-resistance (RON) in heavily carbon doped AlGaN/GaN high electron mobility transistors is shown to be associated with the semi-insulating carbon-doped buffer region. Using transient substrate bias, differences in RON dispersion between transistors fabricated on nominally identical epilayer structures were found to be due to the band-to-band leakage resistance between the buffer and the 2DEG. Contrary to normal expectations, suppression of dynamic RON dispersion in these devices requires a high density of active defects to increase reverse leakage current through the depletion region allowing the floating weakly p-type buffer to remain in equilibrium with the 2DEG
H-terminated vertical GaN PIN diodes: electrical analysis, stability and 2D modeling
No full textreservedNegli ultimi due decenni, il nitruro di gallio (GaN) è emerso come un materiale chiave per la fabbricazione di dispositivi di potenza, grazie alle sue eccezionali proprietà elettriche e termiche. In particolare, i dispositivi verticali in GaN stanno suscitando crescente interesse per applicazioni ad alta tensione e alta corrente, grazie alla migliore scalabilità e alle prestazioni superiori che possono offrire rispetto a quelli laterali. I diodi pn e Schottky verticali in GaN sono spesso utilizzati come piattaforme per studiare le proprietà del materiale, poiché la loro struttura semplice permette di rivelare meccanismi fisici che sarebbero difficili da isolare in architetture più complesse.
Questa tesi si concentra sulla caratterizzazione e modellazione fisica di diodi PIN verticali in GaN cresciuti su un substrato nativo di GaN. La particolarità di questi dispositivi è la loro terminazione al plasma di idrogeno, che si prevede possa influenzare positivamente parametri chiave come la corrente di perdita, la tensione di breakdown e l'affidabilità.
L’obiettivo di questo studio è valutare le prestazioni e l’affidabilità dei diodi, e analizzare l’impatto della passivazione al plasma di idrogeno. È stata inoltre dedicata attenzione ad altri aspetti fondamentali, come l’efficacia del drogaggio con Mg, la qualità dei contatti ohmici e le proprietà elettriche dello strato drogato in modo non intenzionale, per ottenere una comprensione completa del comportamento del dispositivo in applicazioni reali ad alta potenza.
Attraverso misure elettriche (I-V, C-V) e ottiche (elettroluminescenza) eseguite a diverse temperature, sono state studiate le prestazioni dei diodi e i meccanismi fisici che ne guidano il comportamento. Dopo una caratterizzazione preliminare, l’indagine si è concentrata sul regime di conduzione diretta. Sono stati condotti stress in corrente, analizzando l’evoluzione nel tempo dei parametri elettrici e ottici per identificare i meccanismi di degrado e fallimento, e valutare l’affidabilità a lungo termine del dispositivo.
Un aspetto chiave di questo lavoro è l’uso di simulazioni TCAD con Sentaurus, che permettono una comprensione più approfondita dei meccanismi di trasporto e degrado, supportando la formulazione di un modello fisico coerente.Over the past two decades, gallium nitride (GaN) has emerged as a key material for power
device fabrication, due to its exceptional electrical and thermal properties. In particular,
vertical GaN devices are gaining interest for high-voltage and high-current applications,
thanks to the superior scalability and performance they can offer compared to their lateral
counterparts. Vertical GaN pn and Schottky diodes are often used as platforms to study the
material properties, since their simple structure allows to reveal physical mechanisms that
would be difficult to isolate in more complex architectures.
This thesis focuses on the characterization and physical modeling of vertical GaN PIN diodes
grown on a native GaN substrate. The peculiarity of these devices is their hydrogen plasma
termination, which is expected to positively influence key parameters such as leakage current,
breakdown voltage and reliability.
The goal of this study is to assess the performance and reliability of the diodes and evaluate
the impact of hydrogen plasma passivation. Attention was also given to other key aspects such
as the effectiveness of Mg doping, the quality of ohmic contacts and the electrical properties
of the unintentionally doped layer, to get a complete understanding of the device behavior
under high-power real-life applications.
Through electrical (I-V, C-V) and optical (electroluminescence) measurements performed at
different temperatures, we studied the performance of the diodes and the physical mechanisms
driving their behavior. After preliminary characterization, we focused our investigation on the
forward conduction regime. Current stress tests were conducted, studying the evolution over
time of electrical and optical parameters to identify degradation and failure mechanisms and
assess long-term device reliability.
A key aspect of this work is the use of Sentaurus TCAD simulations, that allows a deeper
understanding of transport and degradation mechanisms, assisting in the formulation of a
coherent physical model
Remote temperature mapping of high-power InGaN/GaN MQW flip-chip design LEDs
No full textWe report on the study of heat 2D-distribution in InGaN LEDs with the stress made on local device overheating and
temperature gradients inside the structure. The MQW InGaN/GaN/sapphire blue LEDs are designed as bottom emitting
devices where light escapes the structure through the transparent GaN current spreading layer and sapphire substrate, whereas the LED structure with high-reflectivity Ni/Ag p-contact is bonded to the thermally conductive Si submount by a flip-chip method. The measurements are performed with an IR microscope operating in a time-resolved mode (3-5 μm spectral range, <20 μm spatial and 10 μs temporal resolution), while scanning a heat emission map through a transparent sapphire substrate. We show how current crowding (which is difficult to avoid) causes a local hot region near the n-contact pads and affects the performance of the device at a high injection level
Structural characterization of epitaxial lateral overgrown GaN on patterned GaN/GaAs(001) substrates
No full textEpitaxial lateral overgrown (ELO) cubic GaN (c-GaN) on SiO2 patterned GaN/GaAs(0 0 1) substrates by metalorganic vapor phase epitaxy was investigated using transmission electron microscopy and X-ray diffraction (XRD) measurements. The density of stacking faults (SFs) in ELO c-GaN was similar to6 x 10(8) cm(-2), while that in underlying GaN template was similar to5 x 10(9) cm(-2). XRD measurements showed that the full-width at half-maximum of c-GaN (0 0 2) rocking curve decreased from 33 to 17.8 arcmin, indicating the improved crystalline quality of ELO c-GaN. The mechanism of SF reduction in ELO c-GaN was also discussed. (C) 2002 Elsevier Science B.V. All rights reserved
Pulsed excimer laser annealing of Mg-doped cubic GaN
No full textA KrF (248 nm) excimer laser with a 38 ns pulse width was used to study pulsed laser annealing (PLA) on Mg-doped cubic GaN alms. The laser-induced changes were monitored by photoluminescence (PL) measurement. It indicated that deep levels in as-grown cubic GaN : Mg films were neutralized by H and PLA treatment could break Mg-H-N complex. The evolution of emissions around 426 and 468 nm with different PLA conditions reflected the different activation of the involved deep levels. Rapid thermal annealing (RTA) in N-2 atmosphere reverts the luminescence of laser annealed samples to that of the pre-annealing state. The reason is that most H atoms still remained in the epilayers after PLA due to the short duration of the pulses and reoccupied the original locations during RTA. (C) 2000 Elsevier Science B.V. All rights reserved. PACS: 61.72.Vv; 61.72.Cc; 18.55. -m
Control of residual carbon concentration in GaN high electron mobility transistor and realization of high-resistance GaN grown by metal-organic chemical vapor deposition
No full textGaN films were grown by metal-organic chemical vapor deposition (MOCVD) under various growth conditions. The influences of MOCVD growth parameters, i.e., growth pressure, ammonia (NH3) flux, growth temperature, trimethyl-gallium flux and H-2 flux, on residual carbon concentration ([C]) were systematically investigated. Secondary ion mass spectroscopy measurements show that [C] can be effectively modulated by growth conditions. Especially, it can increase by reducing growth pressure up to two orders of magnitude. High-resistance (HR) GaN epilayer with a resistivity over 1.0 x 10(9) Omega center dot cm is achieved by reducing growth pressure. The mechanism of the formation of HR GaN epilayer is discussed. An AlxGa1-xN/GaN high electron mobility transistor structure with a HR GaN buffer layer and an additional low-carbon GaN channel layer is presented, exhibiting a high two dimensional electron gas mobility of 1815 cm(2)/Vs. (C) 2014 Elsevier B.V. All rights reserved
AlGaN/GaN/InGaN/GaN DH-HEMTs structure with an AlN interlayer grown by MOCVD
No full textA novel AlGaN/GaN/GaN/GaN double heterojunction high electron mobility transistors (DH-HEMTS) structure with an AlN interlayer on sapphire substrate has been grown by MOCVD. The structure featured a 6-10 nm In0.1Ga0.9N layer inserted between the GaN channel and GaN buffer. And wer also inserted one ultrathin. AlN interlayer into the Al/GaN/GaN interface, which significantly enhanced the mobility of two-dimensional electron gas (2DEG) existed in the GaN channel. AFM result of this structure shows a good surface morphology and a low dislocation density, with the root-mean-square roughness (RMS) of 0.196 nm for a scan area of 5 mu m x 5 mu m. Temperature dependent Hall measurement was performed on this sample, and a mobility as high as 1950 cm(2)/Vs at room temperature (RT) was obtained. The sheet carrier density was 9.89 x10(12) cm(2), and average sheet resistance of 327 Omega/sq was achieved. The mobility obtained in this paper is about 50% higher than other results of similar structures which have been reported. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- …
