Chirag Gupta

Chirag Gupta
University of California, Santa Barbara | UCSB · Department of Electrical and Computer Engineering

About

42
Publications
3,930
Reads
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811
Citations
Citations since 2017
34 Research Items
805 Citations
2017201820192020202120222023050100150200
2017201820192020202120222023050100150200
2017201820192020202120222023050100150200
2017201820192020202120222023050100150200

Publications

Publications (42)
Article
Wide bandgap (WBG) semiconductors such as gallium nitride and silicon carbide are rapidly making inroads into the power semiconductor markets dominated by the incumbent silicon. However, the performance of these WBG semiconductors has not reached the ideal material limits and thus, leaves a significant room for improvement. In this regard, for medi...
Article
Nitride based light emitting diodes (LEDs) have demonstrated very high efficiency in the blue and green wavelength ranges. For full color LED based displays, efficient and small sized devices emitting in the three primary colors - red, green and blue are required. While phosphide based red LEDs are highly efficient, high surface recombination veloc...
Article
This article reviews our investigations on the use of patterned porous GaN underlayers to achieve elastic relaxation of lattice mismatched top layers such as InGaN and AlGaN. Thereby the degree of relaxation of the top layers increases with the porosity and associated decrease in mechanical hardness of the porous GaN underlayers as well as with dec...
Article
Ultra-small red micro-LEDs (<10 μ m) with measurable output power have proved difficult to demonstrate. The smallest state-of-the-art red micro-LEDs (AlInGaP) to have exhibited a decent output power of ∼1.75 mW mm ⁻² are 20 μ m × 20 μ m in dimension. InGaN-based red micro-LED development has primarily been impeded due to the large lattice mismatch...
Article
Crack-free 1.3 μm thick elastically relaxed AlxGa1−xN layers were demonstrated on compliant high fill-factor 10 × 10 μm² tile patterned GaN-on-porous-GaN pseudo-substrates (PSs). Porous GaN was utilized as a semi-flexible underlayer. The AlxGa1−xN layer was grown in steps of 200, 300, 400, and 400 nm. While the AlxGa1−xN layer regrown on a co-loade...
Article
In this study, two methods to tune the emission wavelength of micro-LEDs fabricated on tile patterned compliant GaN-on-porous-GaN pseudo-substrates (PSs) are presented. The mechanical flexibility of porous GaN was utilized to relax the strain induced during the growth of light-emitting diode (LED) structures with n- and p-InGaN layers and enhance t...
Article
The compliant behavior of high fill-factor 10 × 10 μm² square patterned 60–140 nm thick GaN-on-porous-GaN tiles was demonstrated by utilizing porous GaN as a semi-flexible underlayer. High resolution x-ray diffraction measurements showed a larger a-lattice constant of InGaN layers deposited on these patterned GaN-on-porous GaN pseudo-substrates in...
Article
In this letter, we report on the demonstration of a Mg-doped GaN/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> N superlattice (SL) based depletion mode p-channel FinFET to improve...
Article
In this Letter, a series of metal-insulator-semiconductor capacitors consisting of Si3N4 dielectrics with different thicknesses on GaN have been fabricated to investigate their interface states. The measurement value extracted from ultraviolet assisted capacitance-voltage methods can be explained by the existence of spatially uniform hole traps in...
Article
Full-text available
The compliant behavior of densely packed 10 × 10 µm2 square patterned InGaN layers on top of porous GaN is demonstrated. The elastic relaxation of the InGaN layers is enabled by the low stiffness of the porous GaN under layer. High resolution X-ray diffraction measurements show that upon InGaN re-growths on these InGaN-on-porous GaN pseudo-substrat...
Article
Fully or partially relaxed micron-sized InGaN patterns with fill factors up to 69% were demonstrated via porosification of the underlying GaN: Si layer. The impact of the porosification etch conditions and the pattern geometry on the degree of InGaN relaxation were studied and monitored via high resolution x-ray diffraction reciprocal space maps. A...
Article
The electrical properties and trapping characteristics of Si3N4 and SiO2 dielectrics grown in situ on (000-1) N-polar GaN by metal organic chemical vapor deposition are investigated in this paper. The fixed charges, densities of near-interface trap states, and interface trap density in N-polar Si3N4 and SiO2 metal insulator semiconductor capacitors...
Article
P-n diodes and metal-oxide-semiconductor-capacitors (MOSCAPs) are integral parts of vertical GaN power MOSFETs. The voltage in the off-state in trench MOSFETs is held by the p-n junction (source-drain) and the MOSCAP (gate-drain). Although the understanding of the reverse bias behavior of the p-n diode and the MOSCAP component is critical, the lite...
Article
Nitrogen polar (N-Polar) GaN high-electron mobility transistors (HEMT) targeting high efficiency in millimeter wave power amplification applications were fabricated on epitaxial layers grown by plasma assisted molecular beam epitaxy (PAMBE) on on-axis semi-insulating bulk GaN substrates. On-state current density of ∼1 A mm ⁻¹ was observed on transi...
Preprint
To realize the full spectrum of advantages that GaN materials system offers, demonstration of p-GaN based devices is valuable. Authors report the first p-field effect transistor (pFET) based on AlGaN/GaN superlattice (SL) grown using MOCVD. Magnesium was used to dope the material in the superlattice. Lowest sheet resistance of 10 k{\Omega}/sq was a...
Article
Hole transport in III-Nitrides (III-Ns) is dominantly dependent on the large effective mass of holes and thus, results in a low hole mobility. First principle band structure calculations suggest that under uniaxial strain, the valence band degeneracy can be broken and the light hole band with lower hole effective mass can be obtained as the topmost...
Article
This letter reports on the dynamic R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> performance of large-area GaN vertical trench MOSFETs (OG-FETs) fabricated on bulk GaN substrates. OG-FETs demonstrated excellent DC performance with a breakdown voltage of 900 V and a R <sub xmlns:mml="http:/...
Article
Al2O3/n-GaN MOS-capacitors grown by metalorganic chemical vapor deposition with in-situ- and ex-situ-formed Al2O3/GaN interfaces were characterized. Capacitors grown entirely in situ exhibited ~4 × 10¹² cm⁻² fewer positive fixed charges and up to ~1 × 10¹³ cm⁻² eV⁻¹ lower interface-state density near the band-edge than did capacitors with ex situ o...
Article
Full-text available
We present a large area in-situ oxide, GaN interlayer based vertical trench MOSFET (OG-FET) with an MOCVD regrown 10 nm UID-GaN interlayer as the channel and 50 nm in-situ Al2O3 as the gate dielectric. The threshold voltage of the device on bulk GaN substrate was 1 V measured at Ion/Ioff = 107. The OG-FET with an area scaled to 0.2 mm2 demonstrated...
Article
In the above paper [1] , the fifth author’s name was printed incorrectly. The correct name is Junqian Liu.
Article
Blanket regrowth studies were performed on GaN trenches with varying widths and optimized for two types of devices—those that required the profile of the trench to be maintained and those that required the complete filling of trenches, i.e., a planar surface after regrowth. Low temperature Al0.22Ga0.78N growth was optimized and used as the marker l...
Article
An improvement in the suppression of surface riding of magnesium from p-GaN:Mg into subsequent layers was achieved via low temperature flow modulation epitaxy. In particular, the slope of the Mg concentration drop was reduced to 5 nm/dec for a growth temperature of 620 °C — the lowest value ever reported for metalorganic chemical vapor deposition....
Article
Gate dielectricplays an integral role in advancing the performance and reliability of GaN-based transistors. Si-alloying of aluminum oxide (Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>...
Article
In this study, we have examined the impact of trench dimensions on the breakdown voltage and on-resistance of trench MOSFETs fabricated on sapphire and bulk GaN substrates. Contrary to simulation studies, the breakdown voltage decreased with an increase in trench dimensions in devices fabricated on sapphire substrates. However, such breakdown volta...
Article
In this study, p-n junction diodes with polarization induced p-type layer are demonstrated on Ga polar (0001) bulk GaN substrates. A quasi-p-type region is obtained by linearly grading the indium composition in un-doped In x Ga1-xN layers from 0% to 5%, taking advantage of the piezoelectric and spontaneous polarization fields which exist in group I...
Article
In this letter, we report on high breakdown voltage in situ oxide, GaN interlayer-based vertical trench MOSFETs (OG-FETs) on bulk GaN substrates. Following our previous work on OG-FETs on GaN on sapphire, utilizing a low damage gate-trench etch and using bulk GaN substrates, a breakdown voltage of 990 V with an ON-resistance 2.6 mQ · cm <sup xmlns:...
Article
GaN trench-gate MOSFETs with m- and a-plane-oriented sidewall channels were fabricated and characterized. The trench-gate MOSFET performance depended strongly on the sidewall-MOS-channel plane orientation. The m-plane-oriented MOS channel devices demonstrated higher channel mobility, higher current density, lower sub-threshold slope, and lower hyst...
Article
Controlled n-type doping down to 2 x10¹⁵ cm⁻³ was achieved in GaN grown on sapphire by MOCVD by balancing the n-type Si doping with respect to the background carbon and oxygen levels. A dopant level of ∼1 x10¹⁶ cm⁻³ displayed a very high mobility of 899 cm² V⁻¹ s⁻¹. High electron mobility in the drift layer leads to a low on resistance and high cur...
Article
The alloying of Al2O3 films with Si is a promising route to improve gate dielectric properties in Si- and wide-bandgap- based MOS devices. Here we present a comprehensive investigation of alloyed film growth by metalorganic chemical vapor deposition (MOCVD) using trimethylaluminum, disilane, and oxygen precursors over a variety of temperature and f...
Article
In this letter, a novel device design to achieve both low on-resistance and enhancement mode operation in a vertical GaN FET is demonstrated. In the traditional trench MOSFET structure, a dielectric is deposited on an n-p-n trenched structure and the channel forms via p-GaN inversion at the dielectric/p-GaN interface. However, this results in a rel...
Article
A polarization-induced three-dimensional hole gas (3DHG) was demonstrated in undoped and compositionally graded InxGa1-xN layers. All samples were grown on Ga-face bulk GaN substrates by metal organic chemical vapor deposition. A high hole concentration of 2.8 10¹⁸cm⁻³ was obtained in a 100-nm-thick InxGa1%xN layer where the indium composition was...
Article
In order to achieve high breakdown voltage in GaN vertical power devices, low threading dislocation density and low background carrier concentration is required. This work demonstrates a decrease in the background carrier concentration and threading dislocation density (TDD) with an increase in the thickness of un-intentionally doped (UID) GaN grow...
Article
In this paper, we report on the growth and electrical characterization of (Al,Si)O dielectrics grown by metalorganic chemical vapor deposition (MOCVD) using trimethylaluminum, oxygen, and silane as precursors. The growth rates, refractive indices, and composition of (Al,Si)O films grown on Si(001) were determined from ellipsometry and XPS measureme...

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