Use of quantum effects as potential qualifying metrics for "quantum grade silicon"

Area of Science:

• Solid-state quantum information science
• Materials science for quantum computing
• Semiconductor device physics

Background:

• Materials deficiencies in solid-state quantum information systems lead to performance limitations such as enhanced relaxation and noise.
• Classical metrics for electronic materials may not adequately qualify materials for quantum devices, necessitating new standards like isotopic enrichment.
• Developing quantum-grade silicon requires establishing reliable metrics and intercomparison methods for novel materials.

Purpose of the Study:

• To investigate the material properties and transport characteristics of locally grown, isotopically enriched 28Si.
• To compare the performance of devices fabricated on 28Si with those on natural abundance silicon (natSi).
• To establish a benchmark for epitaxially grown silicon for quantum applications and contribute to materials standards for quantum-grade silicon.

Main Methods:

• Utilized a custom, mass-selected ion beam deposition technique for isotopic enrichment of 28Si to levels up to 99.99998%.
• Fabricated top-gated Hall bar devices on both isotopically enriched 28Si and adjacent natSi substrates for direct intercomparison.
• Measured electron mobility and Shubnikov-de Haas (SdH) oscillations in longitudinal magnetoresistance at low temperatures (1.9 K).

Main Results:

• Epitaxial silicon achieved 99.99998% 28Si enrichment with chemical purity > 99.97% using molecular beam epitaxy (MBE) techniques.
• Measured maximum electron mobilities of approximately 1740 cm^2/(V*s) on 28Si and 6040 cm^2/(V*s) on natSi at 1.9 K.
• Observed well-developed Shubnikov-de Haas oscillations in both 28Si and natSi devices for magnetic fields B > 2 T, indicating distinct quantum transport phenomena.

Conclusions:

• The study provides crucial transport characteristics for isotopically enriched 28Si, demonstrating its potential for quantum information applications.
• The fabricated devices serve as a benchmark for classical transport in current-state 28Si and epitaxially grown silicon for quantum devices.
• This work underpins the development of materials standards for quantum-grade silicon by offering a comparative analysis of enriched vs. natural silicon.