Technical: Metal-oxide-semiconductor field-effect transistors (MOSFETs) based on group III-V semiconductors have significant potential advantages over silicon-based devices for high-speed, low-power digital integrated circuits. MOSFETs with group III-Sb channels could reduce the switching energy-delay product by an order of magnitude. This project studies gate stacks for scalable n- and p-type MOSFETs with low interface state density and superior channel transport using a novel material system: high dielectric constant (k) oxide on In(Ga)Sb quantum-well channel. The research involves in-situ passivation of III-V channels grown using molecular beam epitaxy in an ultrahigh vacuum environment followed by an in-situ deposition of high-k oxide. A few-monolayer-thick amorphous Si or Al serves as the interface passivation layer and is incorporated into the high-k stack based on HfO2 or other high-k oxides. This approach is expected to reduce interface state density, improve thermal stability, and reduce carrier scattering.
The project addresses basic research issues in a topical area of materials science with high technological relevance. Significant impacts are expected on the microelectronic industry through technology development, commercialization, and the facilitation of further scaling of digital circuits thus providing better, higher quality and less expensive electronics. The project also contributes to education activities through graduate student training, undergraduate minority student participation of research, and promotion of science and technology to the general public.
Among many challenges facing further scaling of Si logic circuits, reduction of power while maintaining the same speed performance (or equivalently, increasing of speed while keeping the power consumption the same) is by all means the biggest obstacle, calling for fundamental changes in digital electronics. Group III-V materials due to their better electronic transport properties have significant potential advantages over currently used silicon (Si), strained Si and silicon-germanium (SiGe) metal-oxide field effect transistors (MOSFETs) for high-speed and low-power digital applications. Although recently there is an enormous progress in n-type MOSFETs with InGaAs channel and high dielectric constant (high-k) oxide, the complimentary MOS (CMOS) logic circuits require similarly improved p-type MOSFETs made from a similar material as n-MOSFETs. So far, the main candidate material for p-MOSFET is Ge. The goal of this project was to research, develop and demonstrate technologies of p-MOSFETs for the next generation integrated circuits based on new group III-antimonides /high-k oxide material system that have significant advantages over Ge-based materials. The following major milestones were reached: (a) Technology for growth of crystalline materials with highly mismatched crystal lattices (group III-antimonides on gallium arsenide) was developed. The technology used metamorphic layers (layers where lattice constant is changed) and allowed for strain control in p-type InGaSb and GaSb quantum well channels. (b) Mobilities and major scattering mechanisms in InGaSb quantum well MOSFET channels with high-k Al2O3 gate oxide were experimentally measured, analyzed; and high-mobility channel was developed. Mobility in the MOSFET channel was found to degrade just by 30% as compared to the best values in quantum wells (Fig. 1a). An interface engineering improved mobility even further, for example, the sample with 3 nm total top barrier thickness demonstrates mobility of 980 cm2/V-s giving sheet resistance of 4.3 kOhm/sq. , very close to the best quantum well parameters. (c) Chemical, imaging and electrical (Fig. 1b) analysis of the interfaces were used to optimize surface treatment of semiconductor prior to the deposition of high-k oxide. Baseline for interface trap density and thermal stability of the semiconductor/oxide interface were obtained for oxides deposited with two techniques: in-situ (without braking ultra-high-vacuum) molecular beam deposition and ex-situ atomic layer deposition. (d) Two novel technology paths were developed for scalable MOSFETs (Fig. 1c-e) utilizing low-temperature processes to improve the interface properties and transistor current. The resultant MOSFETs have shown close to record-high drain currents. Intellectual Merit: An enormous progress in n-type InGaAs metal-oxide-semiconductor field effect transistors (MOSFETs) over the last 5 years makes it finally feasible to introduce "high-mobility channels" into CMOS circuits but requires p-type MOSFETs with similar parameters. The III-Sb/high-k oxide is a novel material system for both p- and n-type MOSFETs that shows amazingly fast progress (compared to Ge) in just the last 3 years. The NSF project has contributed to this progress by novel technologies for heterostructure and interface engineering, benchmarking the material parameters important for transistors, demonstrated two technological paths to overcome low thermal stability of the structures, quantified low interface state densities and superior channel transport in MOS devices. Broader Impact: The NSF funding was used as a seed for development of interdisciplinary expertise and training strategy in physics, materials and technology, 16 publications were produced. (a) 3 PhD students were directly involved in the project, one of them graduated with PhD in May 2011; another one is completing his PhD dissertation targeting Spring 2014 semester graduation; one undergraduate student was on summer 2011 internship. (b) One of the PI's courses significantly revised and matched to 600 graduate level: NNSE618 'Science and Nanoengineering of Semiconductor Materials and Nanostructures'; offered the first time in Fall 2012. (c) Students presented at 6 international conferences and 2 annual MSD Focus Center Meetings. (d) Students participated in preparation and presentations at NANOcarrier days (2011-2013), CNSE Community Day (2011-12) and NanoDays 2012. (e) The NSF funding is a vital contribution to the support and development the infrastructure, expertize and skills of the CNSE personnel; results are is currently used for development of mid-IR quantum cascade laser structures and multi-junction GaAs/GaSb photovoltaics. (f) The acquired knowledge was disseminated through over dozen teleconferences, workshops and seminars to companies and organizations: Intel, Sematech, GLOBALFOUNDRIES, SRC, CNSE.
