Giovanni Isella: Group IV semiconductor heterostructures
Channel: Aula Rostagni UniPadova DFA
Date: 2023-11-02

Speaker: Giovanni Isella
Affiliation: Physics Department of the Politecnico di Milano
Full Title: Group IV semiconductor heterostructures: photonics, spintronics and quantum applications

Abstract:
The epitaxial growth of semiconductor heterostructures offers the unique possibility of combing band-gap and strain engineering to obtain “novel” materials starting from well‑known bulk semiconductors. In the case of Group IV elements, fabrication and processing techniques, developed  for microelectronics applications, can  also be exploited, prior or after epi-growth, to tailor the physical properties of  nano‑ and micro-structures. 

The Colloquium will focus on the physical properties and applications of engineered Si, Ge and Sn epilayers and heterostructures, obtained by combining epitaxial growth, substrate patterning and pulsed-laser melting.

Starting from relatively simple heterostructures and moving towards more complex architectures, the physical properties required for application in photonics, spintronics and qubit applications will be addressed. In particular it will be shown how: the monolithic integration of “bulk” materials with different absorption coefficient enables the fabrication of spectral-sensitive[1] pixels that can be exploited in material recognition; the tailoring of the refractive index by means of alloy or hyperdoping can be exploited for the development of an on-chip sensing platform operating in the mid-infrared[2,3];  substrate patterning and out-of-equilibrium growth can be combined to nucleate 3D epitaxial microcrystals[4] with unique structural and optical properties[5]; and optical selection rules in strained quantum wells can be used to generate an unbalanced spin population enabling the study of spin transport in non-magnetic materials[6]. Finally, the emerging role of hole states in Ge as a platform for spin qubit[7] implementation will be discussed.

References:
[1]  E. Talamas Simola et al., ‘CMOS-Compatible Bias-Tunable Dual-Band Detector Based on GeSn/Ge/Si Coupled Photodiodes’, ACS Photonics 8(7), pp. 2166–2173 (2021)
[2]  L. Baldassarre et al., ‘Midinfrared Plasmon-Enhanced Spectroscopy with Germanium Antennas on Silicon Substrates’, Nano Letters, 15(11),pp. 7225–7231  (2015)
[3]  D. Marris-Morini et al., ‘Germanium-based integrated photonics from near- to mid-infrared applications’, Nanophotonics 7(11), pp. 1781–1793, (2018)
[4]  C. V. Falub et al., ‘Scaling Hetero-Epitaxy from Layers to Three-Dimensional Crystals’, Science 35(6074), pp. 1330–1334 (2012)
[5]  V. Falcone et al., ‘Graphene/Ge microcrystal photodetectors with enhanced infrared responsivity’, APL Photonics 7(4),  046106 (2022)
[6]  F. Bottegoni et al., ‘Spin voltage generation through optical excitation of complementary spin populations’, Nature Materials, 13(8), pp. 790–795 (2014)
[7]  D. Jirovec et al., ‘A singlet-triplet hole spin qubit in planar Ge’, Nature Materials 20(8), pp. 1106–1112, (2021)

Bio:
Giovanni Isella is Full Professor at the Physics Department of the Politecnico di Milano.
His research interests are focused on the epitaxial growth and applications of silicon-germanium (SiGe) heterostructures and devices. Over almost 20 years of activity, G. I. had the chance to explore the wealth of possibilities offered by strain and bandgap engineering in SiGe heterostructures in a variety of application fields including: quantum transport in Ge quantum wells (QW), near- and mid-infrared integrated optics in SiGe waveguides and multiple-QW modulators, thermoelectric generation in low dimensional semiconductors, spintronics in Ge heterostructures, epitaxial growth on patterned substrates, plasmonic effects in heavily doped Ge and the development of qubits based on hole states in Ge. 
 

Link Indico: https://indico.dfa.unipd.it/event/905/