Heat Capacity of Neutron Transmutation Doped Ge Type 18

We present measurements of the heat capacity of neutron transmutation doped (NTD) Ge temperature sensors from 100–300 mK. The NTD Ge sensor studied consists of a 30μm×100μm×250μm block of NTD Ge type 18 with the natural isotopic abundance, a doping of n = 5.6×10^(16) cm^(−3) and ion implanted and metallized contact pads. Each sensor was mounted on a freestanding silicon nitride (Si‐N) pad supported by Si‐N legs each with a cross section in the range 5–10 μm^2. Two of the Si‐N legs were metallized for electrical readout of the NTD Ge sensor. The measured heat capacity of the NTD Ge sensor, which includes the metalization and Si‐N pad, when fit to power law C = C_0T^γ yields C_0 = 4.3pJ/K^γ and γ = 1.6. The thermal conductance, GSi‐N, of the Si‐N support legs was measured over a larger temperature range 80–800 mK. We find G_(si‐N) at temperatures >200 mK of all 4 samples is at or below the 1D or quantum of thermal conductance limit.