  To realize high-temperature operation of Si qubits, deep impurity levels with
large confinement energy, which are hardly thermally excited, have been
introduced into Si wafers. Group II impurity Zn and group VI impurities S and
Se, which are known to form deep levels, were introduced into the Si substrates
by ion implantation. These samples were analyzed for concentration-depth
profiles, energy level depths, and absence of defects. To introduce deep
impurities into thin channels such as 50-nm-thick Si, we found impurity
introduction conditions so that the concentration depth profiles have maximum
value at less than 50 nm from the Si surface. Then, the formation of the deep
levels and absence of defects were experimentally examined. By using the
conditions to introduce deep impurities into Si wafer obtained from the
experiments, single-electron transport at room temperature, high-temperature
operation of qubit, and room-temperature quantum magnetic sensors are
promising.
