Temperature dependence of the Stark shifts of Er$^{3+}$ transitions in Er$_2$O$_3$ thin film on Si (001)

Optical transitions in Er2O3 films grown on Si substrates by using a metal-organic chemical vapor deposition technique were investigated in a wide temperature (300 K ~ 5 K) and spectral (500 nm and 850 nm) ranges. Numerous sharp transitions corresponding to the Er3+ ionic levels, which showed Stark shifts induced by the crystal field were observed. With decreasing temperature from 300 K to 5 K, all transition peaks exhibited spectral red-shifts. We believe that such red-shift behavior is due to a change in the crystal field together with a change in the strain field induced by the film and the substrate with varying temperature. An interesting result is the total amount of red-shift at temperature between 300 K and 5 K. We found that the higher transition energy peaks show bigger red-shifts. This is because the dipole moments between the transition levels are different, which leads to different amounts of the Stark shift.