Epitaxial aluminium gates in ultra-shallow GaAs/AlxGa1-xAs heterostructures for low disorder nanoelectronics

Researchers in the field of nanoelectronics partake in the unending pursuit to reduce device size in order to minimise energy consumption and maximise operation temperature. Device reduction entails decreasing the depth of the conduction channel below the wafer surface, but increased scattering from charge trapped in oxides at the semiconductor surface hinders device performance. In this thesis we report the suppression of surface charge in GaAs/Alx Ga1 xAs systems with ultra-shallow conduction channels by using epitaxial aluminium gates grown in the crystal growth system. We grow aluminium gates in the crystal growth chamber and find it prevents the formation of native surface oxides at the semiconductor surface. In spite of this, if the in situ aluminium gates are grown 50 nm thick, their structure is polycrystalline and the aluminium reacts with the underlying semiconductor layer during device processing, leading to increased scattering in the electron channel. We then show that reducing the epitaxial aluminium thickness to 8 nm yields single-crystal aluminium and prevents the formation of defects at the semiconductor-aluminium interface. This results in greater electron mobility in the channel compared to that of a comparison device with an ex situ gate where the semiconductor surface has oxidised and therefore has charge traps. Next, we investigate growing the epitaxial aluminium gates on different semiconductor layers and find GaAs yields highest electron mobilities. Having optimised the electron mobility in ultra-shallow systems by using epitaxial aluminium gates, we turn to investigating these systems for quantum electronic devices. We fabricate quantum point contacts and evidence the compatibility of these all-epitaxial systems with quantum device fabrication by demonstrating robust and reproducible 1D quantisation. Secondly, we show extremely low levels of charge noise as a result of the suppression of surface charge, further substantiating the suitability of these systems for nanoelectronics. Finally, we explore the use of these systems for artificial lattices and develop a prototype device that confirms the emergence of an artificial bandstructure due to the patterned artificial lattice. Our findings on epitaxial aluminium gates in ultra-shallow GaAs/AlxGa1 xAs systems pave the path for a myriad of nanoelectronic device where high mobility and low levels of charge noise in shallow channels are paramount, such as quantum point contacts, quantum dots, spin quantum bits, and low disorder artificial systems.

Grantor dc:publisher

UNSW, Sydney

Year dc:date

2022

Author dc:creator

• Ashlea Alava, Yonatan

• Epitaxial
• Aluminium
• Quantum point contacts
• Nanoelectronics
• Low disorder
• High electron mobility
• Low charge noise
• anzsrc-for: 401804 Nanoelectronics
• anzsrc-for: 5108 Quantum physics

Statement dc:rights

• open access
• CC BY 4.0
• free_to_read

Licence

• https://purl.org/coar/access_right/c_abf2
• https://creativecommons.org/licenses/by/4.0/

Language dc:language

en

Identifier

https://doi.org/10.26190/unsworks/24344

OAI identifier oai:identifier

oai:unsworks.library.unsw.edu.au:1959.4/100637