Marco G. Pala

Bio: Marco G. Pala is an academic researcher from Université Paris-Saclay. The author has contributed to research in topics: Quantum tunnelling & Scanning gate microscopy. The author has an hindex of 27, co-authored 111 publications receiving 1978 citations. Previous affiliations of Marco G. Pala include University of Pisa & Centre national de la recherche scientifique.

Strain-Induced Performance Improvements in InAs Nanowire Tunnel FETs

Abstract: This paper investigates the electrical performance improvements induced by appropriate strain conditions in n-type InAs nanowire tunnel FETs in the context of a systematic comparison with strained silicon MOSFETs. To this purpose, we exploited a 3-D simulator based on an eight-band k p Hamiltonian within the nonequilibrium Green function formalism. Our model accounts for arbitrary crystal orientations and describes the strain implicitly by a modification of the band structure. The effect of acoustic- and optical-phonon scattering is also accounted for in the self-consistent Born approximation. Our results show that appropriate strain conditions in n-type InAs tunnel FETs induce a remarkable enhancement of Ion with a small degradation of the subthreshold slope, as well as large improvements in the Ioff versus Ion tradeoff for low Ioff and VDD values. Hence, an important widening of the range of Ioff and VDD values where tunnel FETs can compete with strained silicon MOSFETs is obtained.

Spin-orbit coupling and phase coherence in InAs nanowires

Abstract: We investigated the magnetotransport of InAs nanowires grown by selective area metal-organic vapor phase epitaxy. In the temperature range between 0.5 and 30 K reproducible fluctuations in the conductance upon variation of the magnetic field or the back-gate voltage are observed, which are attributed to electron interference effects in small disordered conductors. From the correlation field of the magnetoconductance fluctuations the phase-coherence length lis determined. At the lowest temperatures lis found to be at least 300 nm, while for temperatures exceeding 2 K a monotonous decrease of lwith temperature is observed. A direct observation of the weak antilocalization effect indicating the presence of spin-orbit coupling is masked by the strong magnetoconductance fluctua- tions. However, by averaging the magnetoconductance over a range of gate voltages a clear peak in the magnetoconductance due to the weak antilocalization effect was resolved. By comparison of the experimental data to simulations based on a recursive two-dimensional Green's function approach a spin-orbit scattering length of approximately 70 nm was extracted, indicating the presence of strong spin-orbit coupling.

Interface Traps in InAs Nanowire Tunnel-FETs and MOSFETs—Part I: Model Description and Single Trap Analysis in Tunnel-FETs

Abstract: This paper and the companion work present a full quantum study of the influence of interface traps on the I-V characteristics of InAs nanowire Tunnel-field effect transistors (FETs) and MOSFETs. To this purpose, we introduced a description of interface traps in a simulator based on non equilibrium Green's function formalism, employing an 8 × 8 k·p Hamiltonian and accounting for phonon-scattering. In our model, traps can affect the I-V curves of the transistors both by modifying the device electrostatics and by directly participating the carrier transport. This paper investigates the impact of single trap on the I-V characteristics of Tunnel-FETs by varying the trap energy level, its volume and position, as well as the working temperature. Our 3-D self-consistent simulations show that: 1) even a single trap can deteriorate the inverse subthreshold slope of a nanowire InAs Tunnel-FET; 2) shallow traps have the largest impact on subthreshold slopes; and 3) the inelastic phonon-assisted tunneling through interface traps results in a temperature dependence of the otherwise temperature-independent Tunnel-FETs I-V characteristics.

On the imaging of electron transport in semiconductor quantum structures by scanning-gate microscopy: successes and limitations

Abstract: This paper presents a brief review of scanning-gate microscopy applied to the imaging of electron transport in buried semiconductor quantum structures. After an introduction to the technique and to some of its practical issues, we summarize a selection of its successful achievements found in the literature, including our own research. The latter focuses on the imaging of GaInAs-based quantum rings both in the low-magnetic-field Aharonov-Bohm regime and in the high-field quantum Hall regime. Based on our own experience, we then discuss in detail some of the limitations of scanning-gate microscopy. These include possible tip-induced artefacts, effects of a large bias applied to the scanning tip, as well as consequences of unwanted charge traps on the conductance maps. We emphasize how special care must be paid in interpreting these scanning-gate images.

Superconducting proximity effect in interacting double-dot systems

Abstract: We study subgap transport from a superconductor through a double quantum dot with large on-site Coulomb repulsion to two normal leads. Nonlocal superconducting correlations in the double dot are induced by the proximity to the superconducting lead, detectable in nonlocal Andreev transport that splits Cooper pairs in locally separated, spin-entangled electrons. We find that the $I\text{\ensuremath{-}}V$ characteristics are strongly asymmetric: for a large bias voltage of certain polarity, transport is blocked by populating the double dot with states whose spin symmetry is incompatible with the superconductor. Furthermore, by tuning gate voltages one has access to splitting of the Andreev excitation energies, which is visible in the differential conductance.

Tunnel Field-Effect Transistors: State-of-the-Art

Abstract: Progress in the development of tunnel field-effect transistors (TFETs) is reviewed by comparing experimental results and theoretical predictions against 16-nm FinFET CMOS technology. Experiments lag the projections, but sub-threshold swings less than 60 mV/decade are now reported in 14 TFETs. The lowest measured sub-threshold swings approaches 20 mV/decade, however, the measurements at these lowest values are not based on many points. The highest current at which sub-threshold swing below 60 mV/decade is observed is in the range 1–10 nA/ \({{\mu }}\) m. A common approach to TFET characterization is proposed to facilitate future comparisons.