Low-temperature specific heat of isotopically enriched silicon single crystals

The single crystal of isotopically enriched silicon ( 28 Si) has been made by FZ method with 〈111〉 growth direction. The specific heat measurement at low temperature was performed at the temperature range of 1–140 K. The low-temperature specific heat of 28 Si diverges from Debye T 3 behavior from 14.5 K, and this is in contrast to natural silicon, where deviations from the T 3 behavior occur already at much lower temperature (7.2 K). In addition, the specific heat of 28 Si becomes obviously higher than that of natural silicon at T >20 K.