Himanshu Madan

Fermi level unpinning of GaSb (100) using plasma enhanced atomic layer deposition of Al2O3

N-type and p-type GaSb metal-oxide-semiconductor capacitors (MOSCAPs) with atomic-layer-deposited (ALD) and plasma-enhanced-ALD (PEALD) Al2O3 dielectrics are studied to identify the optimum surface preparation and oxide deposition conditions for a high quality oxide-semiconductor interface. The ALD Al2O3/GaSb MOSCAPs exhibit strongly pinned C-V characteristics with high interface state density (Dit) whereas the PEALD Al2O3/GaSb MOSCAPs show unpinned C-V characteristics (low Dit). The reduction in Sb2O3 to metallic Sb is suppressed for the PEALD samples due to lower process temperature, identified by x-ray photoelectron spectroscopy analysis. Absence of elemental Sb is attributed to unpinning of Fermi level at the PEALD Al2O3/GaSb interface.N-type and p-type GaSb metal-oxide-semiconductor capacitors (MOSCAPs) with atomic-layer-deposited (ALD) and plasma-enhanced-ALD (PEALD) Al2O3 dielectrics are studied to identify the optimum surface preparation and oxide deposition conditions for a high quality oxide-semiconductor interface. The ALD Al2O3/GaSb MOSCAPs exhibit strongly pinned C-V characteristics with high interface state density (Dit) whereas the PEALD Al2O3/GaSb MOSCAPs show unpinned C-V characteristics (low Dit). The reduction in Sb2O3 to metallic Sb is suppressed for the PEALD samples due to lower process temperature, identified by x-ray photoelectron spectroscopy analysis. Absence of elemental Sb is attributed to unpinning of Fermi level at the PEALD Al2O3/GaSb interface.

Small-Signal Response of Inversion Layers in High-Mobility

Ultrahigh-mobility compound semiconductor-based MOSFETs and quantum-well field-effect transistors could enable the next generation of logic transistors operating at low supply voltages since these materials exhibit excellent electron transport properties. While the long-channel In0.53 Ga0.47As MOSFETs exhibit promising characteristics with unpinned Fermi level at the InGaAs-dielectric interface, the high-field channel mobility as well as subthreshold characteristics needs further improvement. In this paper, we present a comprehensive equivalent circuit model that accurately evaluates the experimental small-signal response of inversion layers in In0.53 Ga0.47As MOSFETs fabricated with LaAlO3 gate dielectric and enables accurate extraction of the interface state profile, the trap dynamics, and the effective channel mobility.

\hbox{In}_{0.53}\hbox{Ga}_{0.47}\hbox{As}

Quantitative impedance mapping of the spatially inhomogeneous insulator-to-metal transition (IMT) in vanadium dioxide (VO2) is performed with a lateral resolution of 50 nm through near-field scanning microwave microscopy (SMM) at 16 GHz. SMM is used to measure spatially resolved electronic properties of the phase coexistence in an unstrained VO2 film during the electrically as well as thermally induced IMT. A quantitative impedance map of both the electrically driven filamentary conduction and the thermally induced bulk transition is established. This was modeled as a 2-D heterogeneous resistive network where the distribution function of the IMT temperature across the sample is captured. Applying the resistive network model for the electrically induced IMT case, we reproduce the filamentary nature of electronically induced IMT, which elucidates a cascading avalanche effect triggered by the local electric field across nanoscale insulating and metallic domains.

MOSFETs Made With Thin High-

Experimental gate capacitance (<i>Cg</i>) versus gate voltage data for InAs_0.8Sb_0.2 quantum-well MOSFET (QW-MOSFET) is analyzed using a physics-based analytical model to obtain the quantum capacitance (<i>CQ</i>) and centroid capacitance (<i>C</i>_cent). The nonparabolic electronic band structure of the InAs_0.8Sb_0.2 QW is incorporated in the model. The effective mass extracted from Shubnikov-de Haas magnetotransport measurements is in excellent agreement with that extracted from capacitance measurements. Our analysis confirms that in the operational range of InAs_0.8Sb_0.2 QW-MOSFETs, quantization and nonparabolicity in the QW enhance <i>CQ</i> and <i>C</i>_cent. Our quantitative model also provides an accurate estimate of the various contributing factors toward <i>Cg</i> scaling in future arsenide-antimonide MOSFETs.

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This letter demonstrates, for the first time, enhancement-mode (e-mode) antimonide MOSFETs by integrating a composite high-κ gate stack (3 nm Al₂O₃ -1 nm GaSb) with an ultrathin InAs_0.7Sb_0.3 quantum well (7.5 nm). The MOSFET exhibits record high electron drift mobility of 5200 cm²/V · s at carrier density (N_s) of 1.8 × 10¹² cm^-2, subthreshold slope of 150 mV/dec, I_ON/I_OFF ratio of ~4000× within a voltage window of ~1 V, high I_ON of 40 μA/μm at V_DS of 0.5 V for a 5-μm gate length (L_G) device. The device exhibits excellent pinchoff in the output characteristics with no evidence of impact ionization enabled by enhanced quantization and e-mode operation. RF characterization allows extraction of the intrinsic device metrics (C_gs, C_gd, g_m, v_eff and f_t) and the parasitic resistive and capacitive elements limiting the short-channel device performance.

Dielectrics

This letter proposes a novel application of asymmetric (double-gate) tunnel field-effect transistors (asymmetric TFETs) as a frequency multiplier. Work-function tuning of an asymmetric TFET was used to demonstrate symmetric ambipolar transfer characteristics by TCAD simulation. Unlike the conventional balanced FET-based multiplier, the asymmetric TFET design needs only one transistor for rejecting odd harmonics. Advanced design system simulations are used to compare the performance of an n-type FET and an asymmetric TFET frequency multiplier.

Quantitative mapping of phase coexistence in Mott-Peierls insulator during electronic and thermally driven phase transition.

This paper demonstrates the integration of a composite high-κ gate stack (3.3 nm Al<inf>2</inf>O<inf>3</inf>−1.0 nm GaSb) with a mixed anion InAs<inf>0.8</inf>Sb<inf>0.2</inf> quantum-well field effect transistor (QWFET). The composite gate stack achieves; (i) EOT of 4.2 nm with &#60;10⁻⁷A/cm² gate leakage (ii) low D<inf>it</inf> interface (∼1×10¹² /cm²/eV) (iii) high drift µ of 3,900–5,060 cm²/V-s at N<inf>S</inf> of 5×10¹¹−3×10¹²/cm². The InAs<inf>0.8</inf>Sb<inf>0.2</inf> MOS-QWFETs with composite gate stack exhibit extrinsic (intrinsic) g<inf>m</inf> of 334 (502) µS/µm and drive current of 380 µA/µm at V<inf>DS</inf> = 0.5V for Lg=1µm.

Experimental Determination of Quantum and Centroid Capacitance in Arsenide–Antimonide Quantum-Well MOSFETs Incorporating Nonparabolicity Effect

Antimonide (Sb) quantum-well MOSFETs are demonstrated with an integrated high- κ dielectric (1-nm Al₂O₃ /10-nm HfO₂). The effect of interface trap density <i>D</i>_it on the dc drive current and transconductance <i>gm</i> is studied in detail using split <i>C</i>-<i>V</i>/<i>G</i> -<i>V</i>, pulsed <i>I</i> -<i>V</i>, and radio-frequency measurements. Pulsed <i>I</i>-<i>V</i> measurements show improved on current, transconductance, and subthreshold slope due to reduced charge trapping in the dielectric at high frequencies. The long-channel Sb nMOSFET exhibits effective electron mobility of 6000 cm²/V·s at high field (2 × 10¹²/cm² of charge density <i>Ns</i>), which is 15× higher than Si NMOS inversion layer mobility, and one of the highest values reported for III-V MOSFETs. The short-channel Sb nMOSFET (<i>LG</i> = 150 nm) exhibits a cutoff frequency <i>fT</i> of 120 GHz, an <i>fT</i> × <i>LG</i> product of 18 GHz·μm , and a source-side injection velocity <i>v</i>_eff of 2.7 × 10⁷ cm/s at a drain bias <i>V</i>_DS of 0.75 V and a gate overdrive of 0.6 V.

Enhancement-Mode Antimonide Quantum-Well MOSFETs With High Electron Mobility and Gigahertz Small-Signal Switching Performance

An electrically triggered VO2 RF switch with a record switching cut off frequency (FCO) of 26.5THz was demonstrated. The switch exhibits an isolation better than 35dB and a low 0.5dB insertion loss up-to 50GHz. The switch features a highly linear response with 1-dB compression point (PidB) better than 12dBm and output third-order intercept point (OIP3) better than 44dBm. The fast insulator to metal-transition (IMT) of the VO2 enables the switch to have an electrical-turn on delay of less than 25ns.

Asymmetric Tunnel Field-Effect Transistors as Frequency Multipliers

Graphene’s unique symmetry between p- and n-branches has enabled several interesting device applications; however, short-channel devices often exhibit degraded symmetry. We examine how graphene nanoribbon geometries can improve transfer characteristics and p–n symmetry, as well as reduce Dirac point shift for highly scaled graphene devices. RF graphene transistors utilizing a multiribbon channel are fabricated with channel length down to 100 nm, achieving 4.5-fold improved transconductance, 3-fold improved cutoff frequency, and 2.4-fold improved symmetry compared with sheet devices. The improved performance is linked to reduced contact effects by modeling the extent of charge transfer into the channel as a function of graphene width.