Rama Kambhampati

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}

The paper demonstrates properties of metal oxide semiconductor capacitors fabricated on molecular beam epitaxial In0.53Ga0.47As wafers with the atomic layer deposition ZrO2 gate oxide. The equivalent oxide thickness of 0.8nm was obtained for 5nm thick ZrO2, while the gate leakage current density at VFB+1V was as low as 0.1A∕cm2. Sensitivity of capacitance-voltage characteristics to the metal gate work function along with low frequency dispersion of ∼5%/decade served as a strong evidence of a nonpinned Fermi level at the oxide-InGaAs interface. Both electrical and structural properties remain stable up to 800°C.

MOSFETs Made With Thin High-

An overview of III-V MOSFET technological challenges in comparison to well-established heterostructure-based FET technologies is presented with an emphasis on required properties and possible solutions. Possible approaches to achieve thermodynamically stable high-k gate stack with low interface trap density are reviewed, followed with our results on amorphous Si interface passivation layer (IPL) in-situ deposited on top of GaAs or strained InGaAs MOSFET channels grown by molecular beam epitaxy. Main issues of Si IPL, namely increased equivalent oxide thickness due to IPL oxidation and Si diffusion into the semiconductor channel, are addressed using an in-situ deposited HfO2 with ultrathin (down to 0.25 nm) Si IPL and controlling its bonding state at the interface. Enhancement mode inversion-type MOSFET with HfO2 high-k oxide is demonstrated. The device employs amorphous Si interface passivation layer, sputter-deposited high-k oxide and metal TaN gate and modulation p-doped GaAs/AlGaAs heterostructure with inversion n-channel formed at the interface with the oxide. The MOSFET with equivalent oxide thickness of 3.7 nm and long 100 μm channel have maximum DC transonductance of 0.9 mS/mm, Ion/Ioff = 2×104 (at low Ioff of 30 nA) and effective channel mobility exceeding 1000 cm2/V-s at sheet electron density <2×1012 cm-2.

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Hall electron mobility in buried QW InGaAs channels, grown on InP substrates with HfO2 gate oxide, is analyzed experimentally and theoretically as a function of top barrier thickness and composition, carrier density, and temperature. Temperature slope α in μ ~Tα dependence is changing from α=-1.1 to +1 with the reduction of the top barrier thickness indicating the dominant role of remote Coulomb scattering (RCS) in interface-related contribution to mobility degradation. Insertion of low-k SiOx interface layer formed by oxidation of thin in-situ MBE grown amorphous Si passivation layer has been found to improve the channel mobility, but at the expense of increased EOT. This mobility improvement is also consistent with dominant role of RCS. We were able to a obtain a reasonable match between experiment and simple theory of the RCS assuming the density of charges at the high-k/barrier interface to be in the range of (2-4)×1013 cm-2.

Dielectrics

Insulated gate n-channel enhancement mode InGaAs field effect transistors with the GdScO3 high-k dielectric have been fabricated and studied. The low frequency noise was high indicating a high interface density of traps. Trap density and its dependence on the gate voltage have been extracted from the noise and conductance measurements.

In0.53Ga0.47As based metal oxide semiconductor capacitors with atomic layer deposition ZrO2 gate oxide demonstrating low gate leakage current and equivalent oxide thickness less than 1nm

Homoepitaxially grown InAs quantum dot structures were transferred to Si substrates using oxidation lift-off technology accompanied by direct hydrophilic bonding with Si. Electroluminescence with injection through the substrate and photoluminescence data are presented.

CHALLENGES AND PROGRESS IN III-V MOSFETs FOR CMOS CIRCUITS

calling for effective surface passivation. The role of a Si layer in passivation of the surface states at the GaAs interface has been intensively studied 2,3 . We have recently demonstrated effectiveness of a Si interface layer for in situ passivation of MBE grown GaAs surface enabling good electrical characteristics of MOS capacitors with HfO2 gate dielectric 4 . In this work, we demonstrate performance of enhancement mode N-MOS transistors fabricated on MBE grown GaAs with an in-situ Si passivation layer, ex-situ deposited HfO2 gate dielectric and TaN metal gate.