Electron spin relaxations of phosphorus donors in bulk silicon under large electric field

Daniel K Park,Hyejung Jee,Soonchil Lee,Sejun Park

doi:10.1038/s41598-019-39613-4

Daniel K Park, Hyejung Jee + Show 2 more

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https://doi.org/10.1038/s41598-019-39613-4

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Abstract

Modulation of donor electron wavefunction via electric fields is vital to quantum computing architectures based on donor spins in silicon. For practical and scalable applications, the donor-based qubits must retain sufficiently long coherence times in any realistic experimental conditions. Here, we present pulsed electron spin resonance studies on the longitudinal (T1) and transverse (T2) relaxation times of phosphorus donors in bulk silicon with various electric field strengths up to near avalanche breakdown in high magnetic fields of about 1.2 T and low temperatures of about 8 K. We find that the T1 relaxation time is significantly reduced under large electric fields due to electric current, and T2 is affected as the T1 process can dominate decoherence. Furthermore, we show that the magnetoresistance effect in silicon can be exploited as a means to combat the reduction in the coherence times. While qubit coherence times must be much longer than quantum gate times, electrically accelerated T1 can be found useful when qubit state initialization relies on thermal equilibration.

Highlights

Phosphorus donor spins in silicon (Si:P) are promising candidates for encoding quantum information due to outstanding coherence times and the availability of the mature semiconductor industry
This work reports a detailed experimental study on the spin relaxation times of phosphorus (31P) donor electrons in bulk silicon under electric fields (E0) ranging up to near avalanche breakdown triggered by impact ionization using pulsed electron spin resonance (ESR)
The spin relaxation times of the donor-bound electrons are measured from two Si:P wafers, A and B, with phosphorus concentrations of 2.2 × 1014−4.9 × 1015 P/cm[3] and 3.5 × 1014−6.5 × 1014 P/cm[3], respectively, using a Q-band ESR spectrometer

Summary

Introduction

Phosphorus donor spins in silicon (Si:P) are promising candidates for encoding quantum information due to outstanding coherence times and the availability of the mature semiconductor industry. One and two qubit gate implementations require shifting the donor electron wavefunction to the ionization point, where the electron is shared halfway between donor and Si/SiO2 interface, via electric fields. This scheme allows for the larger inter-qubit spacing than the exchange-based method, which yields sufficient room to place classical control and readout components[16]. The T1 relaxation time changes dramatically under strong electric field near (but before) the avalanche breakdown, and the coherence time T2 is limited by T1 This is attributed to the electric current (I) in the bulk silicon. The reduction in the relaxation times can be minimized by carefully determining the orientation

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