Electron paramagnetic resonance of n -type semiconductors for applications in three-dimensional thermometry

While there are several two-dimensional thermometry techniques that provide excellent spatial, temporal, and time resolution, there is a lack of three-dimensional (3D) thermometry techniques that work for a wide range of materials and offer good resolution in time, space, and temperature. We investigate electron paramagnetic resonance (EPR) of n-type silicon and germanium as a possible means of 3D thermometry. While in germanium the EPR linewidths are too broad for thermometry, EPR linewidths in silicon are reasonably narrow and exhibit a strong temperature dependence. The temperature dependence of the spin-lattice relaxation rate (1/T1) of conduction electrons in n-type Si have been extensively studied for low dopant concentrations and follows a T3 law due to phonon broadening. For heavily doped Si, which is desirable for good SNR for application in thermometry, impurity scattering is expected to decrease the temperature dependence of 1/T1. Our results show that, in heavily doped n-type Si, spin-lattice relaxation induced by impurity scattering does not drastically decrease the temperature dependence of EPR linewidths. In P-doped Si with donor concentration of 7 × 1018/cm3, the EPR linewidth has a T5/2 temperature dependence; the temperature dependence decreases to T3/2 when the donor concentration is 7 × 1019/cm3. While the temperature dependence of linewidth decreases for heavier doping, EPR linewidth is still a sensitive thermometer. We define a figure of merit for SNR for thermometry from EPR linewidths of n-type Si and observe that increasing the doping results in a better SNR for thermometry. Using effective medium theory, we show that EPR linewidth can be a sensitive thermometer for application in 3D thermometry with systems embedding microparticles of heavily doped n-type Si.