D S Rawal - Academia.edu (original) (raw)

Papers by D S Rawal

Research paper thumbnail of Vertically aligned nanowires comprising AlGaN/GaN axial heterostructure by convenient maskless reactive ion etching

Materials Research Express, 2019

Axial heterostructure in a nanowire framework is of interest for next generation electronic and o... more Axial heterostructure in a nanowire framework is of interest for next generation electronic and optoelectronic devices. However, fabrication of such one-dimensional nano-architecture by efficient, economical and convenient routes remains a research challenge. In this direction, a high throughput, cost-effective and easily scalable process has been presented for fabrication of axial AlGaN/GaN heterostructure in vertically aligned nanowires. The process employs BClalt;subagt;3alt;/subagt;/Clalt;subagt;2alt;/subagt; based maskless reactive ion etching (RIE) of epitaxial heterostructures containing high density of threading dislocations. The starting material with high dislocation density comprising nano-dimensional AlGaN layer over microns thick GaN on Sapphire was grown by metal organic vapor phase epitaxy (MOVPE). Using this simple fabrication method, vertically aligned nanowires have been formed with 200-350 nm height and 30-40 nm diameter in high density (10alt;supagt;10alt;/supagt; /cmalt;supagt;2alt;/supagt;). The retention of the nano-dimensional AlGaN layer in the nanowire framework and, hence, formation of axial AlGaN/GaN heterostructures has been confirmed with photoluminescence (PL) spectroscopy and X-Ray diffraction (XRD) measurements. Near cylindrical morphology in the top region of the nanowire and high etch rate indicate that the RIE process used is highly non-selective and the threading dislocation (TD) assisted RIE remains the prime etching mechanism. Tremendous enhancement in optical characteristics of the nanowires has been achieved by surface passivation effects of Poly-3-hexylthiophene (P3HT), a sulfur containing polymer.

Research paper thumbnail of Off‐State Drain Leakage Current Mechanism in GaN High Electron Mobility Transistors from Thermal Storage Test

physica status solidi (a)

Research paper thumbnail of Parameter-based modeling of nanoscale material thermal noise in gallium nitride high-electron-mobility transistors

In this paper, we present an improved analytical model for predicting thermal noise in high-elect... more In this paper, we present an improved analytical model for predicting thermal noise in high-electron-mobility transistors (HEMTs) that considers the material’s intrinsic properties at the nanoscale, specifically, its permittivity and melting point. The developed model is validated by comparing the results obtained from the computer simulation with experimental data for different device structures fabricated from an AlGaN/GaN-based two-dimensional electron gas. Furthermore, it is demonstrated that the nanoscale material’s structural properties have to be considered to estimate the noise characteristics of the HEMT device accurately.

Research paper thumbnail of English

Defence Science Journal, 2009

Research paper thumbnail of Degradation Mechanisms in a Proton Irradiated HEMT with 3DEG Conduction and 3DHG as a Back Barrier

2021 IEEE 21st International Conference on Nanotechnology (NANO)

Research paper thumbnail of Deep Trap Characterization and the Kink Effect in AlGaN/GaN HEMTs

Research paper thumbnail of Nanoscale material parameters based modeling of thermal noise in GaN HEMTs

Semiconductor Science and Technology

Research paper thumbnail of Self heating Effects in GaN High Electron Mobility Transistor for Different Passivation Material

Defence Science Journal

In this paper effect of self-heating has been studied of AlGaN/GaN high electron mobility transis... more In this paper effect of self-heating has been studied of AlGaN/GaN high electron mobility transistor (HEMT) for different passivation layers which is promising device for high power at high frequencies. The different passivation layers used are aluminium oxide (Al2O3), silicon nitride (SiN) and silicon dioxide (SiO2). The device GaN HEMT has been simulated and characterised for its thermal behaviour by the distribution of lattice temperature inside the device using device simulation tool ATLAS from SILVACO. The transfer and output characteristics with and without self-heating has been studied for electrical characterisation. The channel temperature for different passivation observed is 448 K, 456 K and 471 K forAl2O3, SiN and SiO2 respectively. The observed different temperatures are due to difference in their thermal conductivity. This channel temperature information is critical to study the reliability of the device at high power levels.

Research paper thumbnail of Comparative study of Au and Ni/Au gated AlGaN/GaN high electron mobility transistors

AIP Advances

Investigation on de-trapping mechanisms related to non-monotonic kink pattern in GaN HEMT devices... more Investigation on de-trapping mechanisms related to non-monotonic kink pattern in GaN HEMT devices AIP Advances 7, 085209 (2017);

Research paper thumbnail of Memory effect in silicon nitride deposition using ICPCVD technique

Journal of Theoretical and Applied Physics

In this study, a plasma-based low-temperature, low-pressure SiN film deposition is investigated f... more In this study, a plasma-based low-temperature, low-pressure SiN film deposition is investigated for device applications. Ammonia, nitrogen and silane are being used for optimization of the quality of SiN film for device passivation by ICPCVD. Characterization of SiN film is done using elastic recoil detection analysis, AFM, FTIR and ellipsometry. The effect of previous process parameters on subsequent process is called memory effect, which has been investigated by all the characterization techniques. During deposition, this effect has been observed for the same parameters that are used to maintain the stoichiometry of the film. It has been observed that some of the residues of gases used for SiN deposition remain present even after the deposition in the chamber and are carried over for the next deposition process and alter the film property, though parameters such as flow rate, temperature, pressure and time remain fixed. This memory effect alters the film surface roughness and stoi...

Research paper thumbnail of Improvement in DC Pulse Characteristics of AlGaN/GaN HEMT by Employing Dual Metal Gate Structure

Semiconductor Science and Technology

Research paper thumbnail of GaN nanostructures by reactive ion etching: Mask and Maskless approach

Nano-Structures & Nano-Objects

Research paper thumbnail of Design and Fabrication of Multi-finger Field Plate for Enhancement of AlGaN/GaN HEMT Breakdown Voltage

Defence Science Journal

The design and fabrication of gate/source connected multi-finger field plate structures using TCA... more The design and fabrication of gate/source connected multi-finger field plate structures using TCAD ATLAS simulation software is presented. The designed field plate structures are fabricated on indigenous AlGaN/GaN HEMT devices. AlGaN/GaN HEMT devices with field plate structures exhibit about three times improvement in breakdown voltage of device and are in close agreement with the simulation results. Integration of field plates in device have resulted in higher VDS (drain to source voltage) operation and improvement in output power of AlGaN/GaN HEMT devices. Incorporation of field plates also decrease the reverse leakage current of HEMT devices.

Research paper thumbnail of A Highly Selective Low Pressure Inductively Coupled Plasma Etching Process for GaAs Using Photoresist Mask

The Open Plasma Physics Journal

GaAs etch characteristics like etch rate, etch profile sidewall angle, etch surface morphology an... more GaAs etch characteristics like etch rate, etch profile sidewall angle, etch surface morphology and selectivity are studied as a function of Inductively Coupled Plasma (ICP) power and Cl 2 /BCl 3 flow rate ratio in ICP at low pressure (<15mTorr) and low RF bias power (<100W) regime to achieve moderate GaAs etch rate with an-isotropic profiles and smooth surface morphology. The low pressure regime etching at Cl 2 /BCl 3 flow rate ratio of 4:1 has resulted in vertical etch profiles with controlled sidewall angle ~ 84º, smooth surface morphology and good mask selectivity ~15 without significant deposition of CCl x polymer on the etched sidewalls but with limited etch depth ~ 100μm using photoresist mask. The mask selectivity is found to be a strong function of RF bias power and ICP power and a weaker function of process pressure. The resultant etch depth increases with an increase in pressure and flow rate ratio at the expense of etch surface morphology, as the desorption of chemical species limits the etching process at higher Cl 2 flow rates and leaves some of the residue on the surface.

Research paper thumbnail of A Reproducible High Etch Rate ICP Process for Etching of Via-Hole Grounds in 200μm Thick GaAs MMICs

JSTS:Journal of Semiconductor Technology and Science

Research paper thumbnail of Comparison of Two DC Extraction Methods for Mobility and Parasitic Resistances in a HEMT

IEEE Transactions on Electron Devices

Research paper thumbnail of Scaling of current collapse in GaN/AlGaN HEMT for microwave power applications

2015 IEEE MTT-S International Microwave and RF Conference (IMaRC), 2015

Research paper thumbnail of Characterization of ion implanted layers in GaAs and inflence of various parameters on device performance

Research paper thumbnail of Development of GaAs Hyperabrupt Schottky Varactor Diode using Ion-Implanted Active Layer on SI GaAs

We report here the fabrication of ion implanted GaAs hyperabrupt varactor diode that can be integ... more We report here the fabrication of ion implanted GaAs hyperabrupt varactor diode that can be integrated in MMIC process. Varactor diodes with constant sensitivity γ of 0.55–0.65 with Cmax/Cmin varying from 2.5 to 3.5 have been fabricated. Varactors diode geometries with different anode lengths, anode width, single and multiple finger anodes with device area varying from 50 to 6,000 μm2 were fabricated. The breakdown voltage of >10 V have been obtained for all the different value capacitors ranging from 0.16 to 11.2 pF.

Research paper thumbnail of Effect of Process Steps on the Formation of Thin Platinum Silicide Films

Effect of various process steps for determining crystallite quality of thin platinum silicide (Pt... more Effect of various process steps for determining crystallite quality of thin platinum silicide (PtSi) films that find applications for making IR detectors was studied by X-ray diffraction (XRD) method. The films in the range of 50-150 Å were grown on p- as well as on n- type silicon substrates by evaporation and sputtering techniques. Effect of annealing, run-to-run variation, pre-sputter etch etc. were studied. Results indicate that after annealing, sharp PtSi peaks along <011> at 29.1 degrees, <112> at 42.8 degrees and <211> at 43.9 degrees are observed for the cases wherein Pt metal was deposited by sputtering techniques. No significant differences were observed between films made on p- or n- type Silicon substrates. Furthermore, in case of deposition by sputtering technique, it was found that pre-sputter etch step does not improve further the quality of the PtSi films.

Research paper thumbnail of Vertically aligned nanowires comprising AlGaN/GaN axial heterostructure by convenient maskless reactive ion etching

Materials Research Express, 2019

Axial heterostructure in a nanowire framework is of interest for next generation electronic and o... more Axial heterostructure in a nanowire framework is of interest for next generation electronic and optoelectronic devices. However, fabrication of such one-dimensional nano-architecture by efficient, economical and convenient routes remains a research challenge. In this direction, a high throughput, cost-effective and easily scalable process has been presented for fabrication of axial AlGaN/GaN heterostructure in vertically aligned nanowires. The process employs BClalt;subagt;3alt;/subagt;/Clalt;subagt;2alt;/subagt; based maskless reactive ion etching (RIE) of epitaxial heterostructures containing high density of threading dislocations. The starting material with high dislocation density comprising nano-dimensional AlGaN layer over microns thick GaN on Sapphire was grown by metal organic vapor phase epitaxy (MOVPE). Using this simple fabrication method, vertically aligned nanowires have been formed with 200-350 nm height and 30-40 nm diameter in high density (10alt;supagt;10alt;/supagt; /cmalt;supagt;2alt;/supagt;). The retention of the nano-dimensional AlGaN layer in the nanowire framework and, hence, formation of axial AlGaN/GaN heterostructures has been confirmed with photoluminescence (PL) spectroscopy and X-Ray diffraction (XRD) measurements. Near cylindrical morphology in the top region of the nanowire and high etch rate indicate that the RIE process used is highly non-selective and the threading dislocation (TD) assisted RIE remains the prime etching mechanism. Tremendous enhancement in optical characteristics of the nanowires has been achieved by surface passivation effects of Poly-3-hexylthiophene (P3HT), a sulfur containing polymer.

Research paper thumbnail of Off‐State Drain Leakage Current Mechanism in GaN High Electron Mobility Transistors from Thermal Storage Test

physica status solidi (a)

Research paper thumbnail of Parameter-based modeling of nanoscale material thermal noise in gallium nitride high-electron-mobility transistors

In this paper, we present an improved analytical model for predicting thermal noise in high-elect... more In this paper, we present an improved analytical model for predicting thermal noise in high-electron-mobility transistors (HEMTs) that considers the material’s intrinsic properties at the nanoscale, specifically, its permittivity and melting point. The developed model is validated by comparing the results obtained from the computer simulation with experimental data for different device structures fabricated from an AlGaN/GaN-based two-dimensional electron gas. Furthermore, it is demonstrated that the nanoscale material’s structural properties have to be considered to estimate the noise characteristics of the HEMT device accurately.

Research paper thumbnail of English

Defence Science Journal, 2009

Research paper thumbnail of Degradation Mechanisms in a Proton Irradiated HEMT with 3DEG Conduction and 3DHG as a Back Barrier

2021 IEEE 21st International Conference on Nanotechnology (NANO)

Research paper thumbnail of Deep Trap Characterization and the Kink Effect in AlGaN/GaN HEMTs

Research paper thumbnail of Nanoscale material parameters based modeling of thermal noise in GaN HEMTs

Semiconductor Science and Technology

Research paper thumbnail of Self heating Effects in GaN High Electron Mobility Transistor for Different Passivation Material

Defence Science Journal

In this paper effect of self-heating has been studied of AlGaN/GaN high electron mobility transis... more In this paper effect of self-heating has been studied of AlGaN/GaN high electron mobility transistor (HEMT) for different passivation layers which is promising device for high power at high frequencies. The different passivation layers used are aluminium oxide (Al2O3), silicon nitride (SiN) and silicon dioxide (SiO2). The device GaN HEMT has been simulated and characterised for its thermal behaviour by the distribution of lattice temperature inside the device using device simulation tool ATLAS from SILVACO. The transfer and output characteristics with and without self-heating has been studied for electrical characterisation. The channel temperature for different passivation observed is 448 K, 456 K and 471 K forAl2O3, SiN and SiO2 respectively. The observed different temperatures are due to difference in their thermal conductivity. This channel temperature information is critical to study the reliability of the device at high power levels.

Research paper thumbnail of Comparative study of Au and Ni/Au gated AlGaN/GaN high electron mobility transistors

AIP Advances

Investigation on de-trapping mechanisms related to non-monotonic kink pattern in GaN HEMT devices... more Investigation on de-trapping mechanisms related to non-monotonic kink pattern in GaN HEMT devices AIP Advances 7, 085209 (2017);

Research paper thumbnail of Memory effect in silicon nitride deposition using ICPCVD technique

Journal of Theoretical and Applied Physics

In this study, a plasma-based low-temperature, low-pressure SiN film deposition is investigated f... more In this study, a plasma-based low-temperature, low-pressure SiN film deposition is investigated for device applications. Ammonia, nitrogen and silane are being used for optimization of the quality of SiN film for device passivation by ICPCVD. Characterization of SiN film is done using elastic recoil detection analysis, AFM, FTIR and ellipsometry. The effect of previous process parameters on subsequent process is called memory effect, which has been investigated by all the characterization techniques. During deposition, this effect has been observed for the same parameters that are used to maintain the stoichiometry of the film. It has been observed that some of the residues of gases used for SiN deposition remain present even after the deposition in the chamber and are carried over for the next deposition process and alter the film property, though parameters such as flow rate, temperature, pressure and time remain fixed. This memory effect alters the film surface roughness and stoi...

Research paper thumbnail of Improvement in DC Pulse Characteristics of AlGaN/GaN HEMT by Employing Dual Metal Gate Structure

Semiconductor Science and Technology

Research paper thumbnail of GaN nanostructures by reactive ion etching: Mask and Maskless approach

Nano-Structures & Nano-Objects

Research paper thumbnail of Design and Fabrication of Multi-finger Field Plate for Enhancement of AlGaN/GaN HEMT Breakdown Voltage

Defence Science Journal

The design and fabrication of gate/source connected multi-finger field plate structures using TCA... more The design and fabrication of gate/source connected multi-finger field plate structures using TCAD ATLAS simulation software is presented. The designed field plate structures are fabricated on indigenous AlGaN/GaN HEMT devices. AlGaN/GaN HEMT devices with field plate structures exhibit about three times improvement in breakdown voltage of device and are in close agreement with the simulation results. Integration of field plates in device have resulted in higher VDS (drain to source voltage) operation and improvement in output power of AlGaN/GaN HEMT devices. Incorporation of field plates also decrease the reverse leakage current of HEMT devices.

Research paper thumbnail of A Highly Selective Low Pressure Inductively Coupled Plasma Etching Process for GaAs Using Photoresist Mask

The Open Plasma Physics Journal

GaAs etch characteristics like etch rate, etch profile sidewall angle, etch surface morphology an... more GaAs etch characteristics like etch rate, etch profile sidewall angle, etch surface morphology and selectivity are studied as a function of Inductively Coupled Plasma (ICP) power and Cl 2 /BCl 3 flow rate ratio in ICP at low pressure (<15mTorr) and low RF bias power (<100W) regime to achieve moderate GaAs etch rate with an-isotropic profiles and smooth surface morphology. The low pressure regime etching at Cl 2 /BCl 3 flow rate ratio of 4:1 has resulted in vertical etch profiles with controlled sidewall angle ~ 84º, smooth surface morphology and good mask selectivity ~15 without significant deposition of CCl x polymer on the etched sidewalls but with limited etch depth ~ 100μm using photoresist mask. The mask selectivity is found to be a strong function of RF bias power and ICP power and a weaker function of process pressure. The resultant etch depth increases with an increase in pressure and flow rate ratio at the expense of etch surface morphology, as the desorption of chemical species limits the etching process at higher Cl 2 flow rates and leaves some of the residue on the surface.

Research paper thumbnail of A Reproducible High Etch Rate ICP Process for Etching of Via-Hole Grounds in 200μm Thick GaAs MMICs

JSTS:Journal of Semiconductor Technology and Science

Research paper thumbnail of Comparison of Two DC Extraction Methods for Mobility and Parasitic Resistances in a HEMT

IEEE Transactions on Electron Devices

Research paper thumbnail of Scaling of current collapse in GaN/AlGaN HEMT for microwave power applications

2015 IEEE MTT-S International Microwave and RF Conference (IMaRC), 2015

Research paper thumbnail of Characterization of ion implanted layers in GaAs and inflence of various parameters on device performance

Research paper thumbnail of Development of GaAs Hyperabrupt Schottky Varactor Diode using Ion-Implanted Active Layer on SI GaAs

We report here the fabrication of ion implanted GaAs hyperabrupt varactor diode that can be integ... more We report here the fabrication of ion implanted GaAs hyperabrupt varactor diode that can be integrated in MMIC process. Varactor diodes with constant sensitivity γ of 0.55–0.65 with Cmax/Cmin varying from 2.5 to 3.5 have been fabricated. Varactors diode geometries with different anode lengths, anode width, single and multiple finger anodes with device area varying from 50 to 6,000 μm2 were fabricated. The breakdown voltage of >10 V have been obtained for all the different value capacitors ranging from 0.16 to 11.2 pF.

Research paper thumbnail of Effect of Process Steps on the Formation of Thin Platinum Silicide Films

Effect of various process steps for determining crystallite quality of thin platinum silicide (Pt... more Effect of various process steps for determining crystallite quality of thin platinum silicide (PtSi) films that find applications for making IR detectors was studied by X-ray diffraction (XRD) method. The films in the range of 50-150 Å were grown on p- as well as on n- type silicon substrates by evaporation and sputtering techniques. Effect of annealing, run-to-run variation, pre-sputter etch etc. were studied. Results indicate that after annealing, sharp PtSi peaks along <011> at 29.1 degrees, <112> at 42.8 degrees and <211> at 43.9 degrees are observed for the cases wherein Pt metal was deposited by sputtering techniques. No significant differences were observed between films made on p- or n- type Silicon substrates. Furthermore, in case of deposition by sputtering technique, it was found that pre-sputter etch step does not improve further the quality of the PtSi films.