Mudassar Meer

Bio: Mudassar Meer is an academic researcher from Indian Institute of Technology Bombay. The author has contributed to research in topics: Ohmic contact & Transconductance. The author has an hindex of 7, co-authored 13 publications receiving 95 citations. Previous affiliations of Mudassar Meer include Indian Institutes of Technology.

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.

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.

Source extension region scaling for AlGaN/GaN high electron mobility transistors using non-alloyed ohmic contacts

Abstract: Here we have demonstrated AlGaN/GaN based high electron mobility transistors with scaled source extension regions using non-alloyed ohmic contacts to two-dimensional electron gas (2-DEG). We show that the scaling of the extension region has profound impact on the device radio frequency (RF) response and the performance peaks at an optimum extension region length. The unity current gain (fT) and power gain frequencies (fmax) have been found to be 79.6 and 96.2 GHz, respectively, for a 260 nm gate length (Lg) and 120 nm extension region length. The devices show a very large fT × Lg product of 20.7 GHz μm at the optimum extension length. The presence of the optimum extension length and the equivalence of source extension and gate length scaling may serve as additional design rules for high performance HEMTs.

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.

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.

Strong Size Dependency on the Carrier and Photon Dynamics in InGaN/GaN Single Nanowalls Determined Using Photoluminescence and Ultrafast Transient Absorption Spectroscopy.

Abstract: Here, we have demonstrated strong size dependency of quasi-equilibrium and nonequilibrium carrier and photon dynamics in InGaN/GaN single nanowalls using photoluminescence and transient absorption spectroscopy. We demonstrate that two-dimensional carrier confinement, strain relaxation, and modified density of states lead to a reduced Stokes shift, smaller full width at half-maxima, increased exciton binding energy, and reduced nonradiative recombination. The ultrafast transient spectroscopy shows that carrier capture is a two-step process dominated by optical phonons and carrier–carrier scattering in succession. The carrier capture is a strongly size-dependent process and becomes slower due to modulation of the density of available states for progressively decreasing nanowall sizes. The slowest process is the electron–hole recombination, which is also extremely size-dependent and the rate increases by almost an order of magnitude in comparison to that of quantum-well structures. Electron–hole wave functio...

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.