n-Type diamond synthesized with tert-butylphosphine for long spin coherence times of perfectly aligned NV centers

TL;DR

This study demonstrates a safer, effective method for synthesizing phosphorus-doped n-type diamond with aligned NV centers and long spin coherence times, advancing quantum device fabrication.

Contribution

It introduces tert-butylphosphine as a less toxic precursor for n-type diamond growth with controlled impurity levels and demonstrates long coherence times in aligned NV centers.

Findings

Achieved n-type diamond with Hall mobility up to 422 cm²/(Vs)

Extended NV center spin coherence time to 1.62 ms

Successfully aligned NV centers along [111] direction

Abstract

The longest spin coherence times for nitrogen-vacancy (NV) centers at room temperature have been achieved in phosphorus-doped n-type diamond. However, difficulty controlling impurity incorporation and the utilization of highly toxic phosphine gas in the chemical vapor deposition (CVD) technique pose problems for the growth of n-type diamond. In the present study, n-type diamond samples were synthesized by CVD using tert-butylphosphine, which is much less toxic than phosphine. The unintentional incorporation of nitrogen was found to be suppressed by incrementally increasing the gas flow rates of H2 and CH$_4$. Hall measurements confirmed n-type conduction in three measured samples prepared under different growth conditions. The highest measured Hall mobility at room temperature was 422 cm$^2$/(Vs). In the sample with the lowest nitrogen concentration, the spin coherence time ($T_2$) increased to 1.62 $\pm$ 0.10 ms. Optically detected magnetic resonance spectra indicated that all of the measured NV centers were aligned along the [111] direction. This study provides appropriate CVD conditions for growing phosphorus-doped n-type diamond with perfectly aligned NV centers exhibiting long spin coherence times, which is important for the production of quantum diamond devices.