Vivek Kumar Surana

Bio: Vivek Kumar Surana is an academic researcher from Indian Institute of Technology Bombay. The author has contributed to research in topics: Transconductance & Passivation. The author has an hindex of 3, co-authored 4 publications receiving 39 citations.

Thermally Grown TiO 2 and Al 2 O 3 for GaN-Based MOS-HEMTs

Abstract: We have demonstrated the potential use of thermally grown TiO2 and Al2O3 oxides as gate dielectrics for GaN-based high-electron-mobility-transistors. TiO2 and Al2O3 are found to provide negative and positive band offsets with AlGaN, respectively. A significant performance improvement on various device characteristics provides evidence for its potential use. The oxides are formed by a combination of predeposition of a thin film and followed by oxidation in pure O2 environment. The formation and thickness of the oxides are confirmed through the X-ray photoelectron spectroscopy and the transmission electron microscopy. The performance improvement for TiO2- and Al2O3-based oxide gates have been identified in terms of a ideality factor and a reduction in the gate leakage current in comparison with that of control devices. This is further augmented by an increase in the ${n}_{s}\times \mu $ product. The ON/OFF current ratio and turn-ON voltage increase by 2–3 orders of magnitude and 0.3–0.6, respectively, for the Schottky diodes. The negative shift on the capacitance–voltage characteristics is also found to be minimal, indicating higher gate coupling with thermally grown oxides.

Gate Current Reduction and Improved DC/RF Characteristics in GaN-Based MOS-HEMTs Using Thermally Grown TiO 2 as a Dielectric

Abstract: This paper demonstrates a reduction in the gate leakage current and improvement in transistor characteristics in thermally grown TiO2/AlGaN/GaN heterostructure-based metal–oxide–semiconductor high-electron-mobility transistors (MOS-HEMTs). In contrast to the conventional AlGaN/GaN HEMTs, thermionic field emission through gate is not the dominant current transport mechanism for the thermally grown TiO2/AlGaN interface. The gate current is greatly affected by the properties of the oxide material and oxide–semiconductor interface in addition to the property of the barrier layer. The MOS-HEMTs with a 3.4-nm-thick TiO2 gate insulator exhibits a low gate leakage current of 10−8 Acm−2, which leads to superior device performances in terms of saturation drain current, peak transconductance, subthreshold swing, and unity gain frequency of 620 mA/mm, 158 mS/mm, 75 mV/decade, and 7 GHz, respectively, for a 400-nm gate length device. This is further augmented by an increase in ON/OFF ratio to ${5}\times {10}^{{8}}$ and a large reduction in the subthreshold leakage current by at least two orders of magnitude in comparison to that of a control HEMT. Trap-assisted tunneling (TAT) and Poole–Frenkel (PF) emission are found to be the dominant current mechanisms for gate leakage at high temperatures and moderate electric field. The activation energy of traps in PF emission is found to be 0.49 eV, and the extracted trap energy levels for the TAT are found to be in the range of 1.7–2.2 eV. The reverse bias current is found to saturate at high voltages when the field across the diode also saturates. The transistor characteristics improvement is largely ascribed to an increase in 2-D electron gas (2DEG) density.

Realization of high quality silicon nitride deposition at low temperatures

Abstract: This work demonstrates the low temperature thin-film deposition of silicon nitride ( SiN x) for III-nitride-based high electron mobility transistors using inductively coupled plasma chemical vapor deposition. It is observed that the nonlinear dependency of the deposition temperature and gas flow rates have a profound impact on the film quality. The process parameter space is scanned and the optimum film quality is achieved, which is verified with physical and electrical characterizations. The best quality film is achieved at a deposition temperature of 380 °C demonstrating near ideal stoichiometry with negligible hydrogen ( <5%) and oxygen ( <3%) concentrations. In addition, the optimized film is found to have zero pinholes even at a thickness of 10 nm and is uniform over a large area with an rms roughness of 0.58 nm. The deposited films are characterized by atomic force microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The dielectric strength and dielectric constant of these films are determined from current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the metal-insulator-metal structure, respectively. For the best quality film, the values of dielectric strength and dielectric constant are measured to be ∼ 8 MV/cm and ∼ 7.5, respectively. A metal-insulator-semiconductor-heterostructure (metal/SiN x/AlGaN/GaN) capacitor is fabricated with the optimized recipe for interface characterization. The density of slow traps is determined from the hysteresis in the C-V curve and found to be 7.38 × 10 10 cm − 2. The frequency dependent conductance method is also used to investigate the trap density. The trap state density is found to be 1.67 × 10 12 cm − 2 eV − 1 at 0.29 eV below conduction band.

Tensile strain and Fermi level alignment in thermally grown TiO2 and Al2O3 based AlGaN/GaN MOS-HEMTs

Abstract: This work reports on the origin of performance improvement for thermally grown TiO2 and Al2O3 based AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs). The oxides have been used as gate dielectrics and passivation layer. High resolution X-ray diffraction, X-ray photoelectron spectroscopy, and transistor characteristics are analysed to investigate the improvements in the two dimensional electron gas (2DEG) concentration. The HRXRD analysis reveals that in-plane tensile stress of AlGaN layer is increased by 23% (12%) for TiO2 (Al2O3) sample as compared to that of an as-grown sample. The induced tensile stress in the AlGaN barrier layer enhances the piezoelectric polarization charges which effectively improve the carrier confinement and mobility at the interface. The improvement in the DC characteristics is observed as a reduction in the gate leakage current without deteriorating gate control and transconductance. The output characteristics of TiO2 (Al2O3) based MOS-HEMTs have shown a 60% (40%) increment in the maximum saturation drain current and 50% (40%) increment in the transconductance as compared to that of a control sample. The RF characteristics also show similar order of improvements.

Performance Improvement in AlGaN/GaN High‐Electron‐Mobility Transistors by Low‐Temperature Inductively Coupled Plasma–Chemical Vapor Deposited SiN x as Gate Dielectric and Surface Passivation

Abstract: This work demonstrates performance improvements in AlGaN/GaN metal–insulator–semiconductor high‐electron‐mobility transistors (MIS‐HEMTs) using low‐temperature inductively coupled plasma chemical vapor deposited (ICP–CVD) silicon nitride (SiN x ). The low‐temperature SiN x is used for both device passivation and gate dielectric. The bandgap of SiN x (4.9 eV) and AlGaN/SiN x type‐II staggered band alignment (ΔE c = 1.4 eV) are determined using ultraviolet‐visible spectroscopy and ultraviolet photoelectron spectroscopy, respectively. The SiN x layer effectively increases the in‐plane tensile strain in the AlGaN barrier layer. The tensile strain increases by 0.08% for a 150 nm SiN x layer. The corresponding increase in the piezoelectric polarization and 2D electron gas (2DEG) density is 1.5 × 1012 and 1.44 × 1012 cm−2, respectively. The transistor's on‐resistance decreases to 9.33 Ω mm compared with 14 Ω mm measured for the control devices with gate length 1 μm and source and drain separation of 11 μm. The gate leakage current reduces by more than three orders of magnitude. The I ON/I OFF ratio increases by two orders of magnitude. The improvements in the physical and electrical properties of the low‐temperature‐deposited ICP–CVD SiN x MIS‐HEMTs make it a viable candidate for low‐thermal‐budget fabrication. This nitride can be used with non‐alloyed Ohmic contacts on GaN for extremely low‐thermal‐budget transistors.

Properties group III nitrides

Abstract: Properties Group III Nitrides, James H. Edgar: Editor. Published by: INSPEC, the Institution of Electrical Engineers, London, UK Tel/fax: [44](0) 1438 3 1 3 3 1 1 / 3 6 0 0 7 9 . ISBN: 0-85296 818 3. There are several families of s e m i c o n d u c t o r s , the most famil iar p r o b a b l y being the elemental semic o n d u c t o r s Si and Ge, located in column IVB of the periodic table. The IIIV compounds and alloys are formed from various combinations of atoms located in columns IIIB and VB. Interest in the IIINitrides materials, which include the direct band gap semiconductors InN, GaN, and A1N centres on the combina t ion of the wide energy gap and high electron mobility obtainable in InN, the blue electroluminescence characteristic o f G a N and the insulating and piezoelectric p rope r t i e s o f AIN and GaN. By contrast films of BN, which is an indirect bandgap semiconductor , have been of interest primarily for wearand corrosion-resistant, electrically insulating and passivating surfaces. This is volume 11 of the Electronic Materials Information Service (EMIS) series and as with the others it organises the most current available data and provides a useful reference to the IIINitrides research community. Chapter 1 review the basic physical properties of the g roup III ni t r ides . Chapters 2 and 3 cover phase diagrams and electrical t ranspor t properties. Chapters 4 and 5 contain the band structure of pure group III nitrides and alloys. The important fundamental optical functions are discussed in Chapter 6. Photoluminescence, cathodo luminescence , R a m a n and IR reflection chracteristics of III-Nitrides are reviewed in Chapters 7 and 8. Chapter 9 provides a discussion of defects and impurities in III-Nitrides. Finally, Chapte r 10 reviews the proper t ies of interfaces, both metallic and semiconducting heteroj u n c t i o n s , f o r m e d with group III-Nitrides. This book aims to provide a useful reference for researchers in this field, as well as a starting point and guide for those who are seeking to further exploit the unique properties of the I I I -Ni t r ides based compounds and their alloys. Finally, I would like to co n g ra tu l a t e the ed i to r and the authors for their considerable efforts and I hope that this volume will serve as a complete reference for the III-Nitrides technology, and stimulate further work in this exciting and expanding field.

Ti/Au/Al/Ni/Au Low Contact Resistance and Sharp Edge Acuity for Highly Scalable AlGaN/GaN HEMTs

Abstract: In this letter, we have reported a novel metal scheme Ti/Au/Al/Ni/Au for ohmic contact on AlGaN/GaN high-electron-mobility transistors. The reported metal scheme is observed to show minimum metal out-diffusion and sharp edge acuity at high-temperature annealing, which facilitates aggressive scaling of source–drain separation ( ${L} _{\textsf {SD}}$ ). We have demonstrated ${L} _{\textsf {SD}}$ as low as 300 nm with gate length ( ${L} _{\textsf {g}}$ ) of 100 nm for this metal stack. We observed improvement in ON-resistance ( ${R} _{\mathrm{\scriptscriptstyle ON}}$ ) from 3 to $1.25~\Omega \cdot$ mm, transconductance ( ${g} _{\textsf {m}}$ ) from 276 to 365 mS/mm, saturation drain current ( ${I} _{\textsf {DS,sat}}$ ) from 906 to 1230 mA/mm, and unity current gain frequency ( ${f} _{\textsf {T}}$ ) from 70 to 93 GHz by scaling ${L} _{\textsf {SD}}$ from $3~\mu \text{m}$ to 300 nm. The gate lengths for all devices were 100 nm.

Gate Current Reduction and Improved DC/RF Characteristics in GaN-Based MOS-HEMTs Using Thermally Grown TiO 2 as a Dielectric

Abstract: This paper demonstrates a reduction in the gate leakage current and improvement in transistor characteristics in thermally grown TiO2/AlGaN/GaN heterostructure-based metal–oxide–semiconductor high-electron-mobility transistors (MOS-HEMTs). In contrast to the conventional AlGaN/GaN HEMTs, thermionic field emission through gate is not the dominant current transport mechanism for the thermally grown TiO2/AlGaN interface. The gate current is greatly affected by the properties of the oxide material and oxide–semiconductor interface in addition to the property of the barrier layer. The MOS-HEMTs with a 3.4-nm-thick TiO2 gate insulator exhibits a low gate leakage current of 10−8 Acm−2, which leads to superior device performances in terms of saturation drain current, peak transconductance, subthreshold swing, and unity gain frequency of 620 mA/mm, 158 mS/mm, 75 mV/decade, and 7 GHz, respectively, for a 400-nm gate length device. This is further augmented by an increase in ON/OFF ratio to ${5}\times {10}^{{8}}$ and a large reduction in the subthreshold leakage current by at least two orders of magnitude in comparison to that of a control HEMT. Trap-assisted tunneling (TAT) and Poole–Frenkel (PF) emission are found to be the dominant current mechanisms for gate leakage at high temperatures and moderate electric field. The activation energy of traps in PF emission is found to be 0.49 eV, and the extracted trap energy levels for the TAT are found to be in the range of 1.7–2.2 eV. The reverse bias current is found to saturate at high voltages when the field across the diode also saturates. The transistor characteristics improvement is largely ascribed to an increase in 2-D electron gas (2DEG) density.

Realization of high quality silicon nitride deposition at low temperatures

Abstract: This work demonstrates the low temperature thin-film deposition of silicon nitride ( SiN x) for III-nitride-based high electron mobility transistors using inductively coupled plasma chemical vapor deposition. It is observed that the nonlinear dependency of the deposition temperature and gas flow rates have a profound impact on the film quality. The process parameter space is scanned and the optimum film quality is achieved, which is verified with physical and electrical characterizations. The best quality film is achieved at a deposition temperature of 380 °C demonstrating near ideal stoichiometry with negligible hydrogen ( <5%) and oxygen ( <3%) concentrations. In addition, the optimized film is found to have zero pinholes even at a thickness of 10 nm and is uniform over a large area with an rms roughness of 0.58 nm. The deposited films are characterized by atomic force microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The dielectric strength and dielectric constant of these films are determined from current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the metal-insulator-metal structure, respectively. For the best quality film, the values of dielectric strength and dielectric constant are measured to be ∼ 8 MV/cm and ∼ 7.5, respectively. A metal-insulator-semiconductor-heterostructure (metal/SiN x/AlGaN/GaN) capacitor is fabricated with the optimized recipe for interface characterization. The density of slow traps is determined from the hysteresis in the C-V curve and found to be 7.38 × 10 10 cm − 2. The frequency dependent conductance method is also used to investigate the trap density. The trap state density is found to be 1.67 × 10 12 cm − 2 eV − 1 at 0.29 eV below conduction band.