Infrared Absorption of Mg2 Sn Single Crystals

摘要

Infrared transmission and reflection measurements of n- and p-type semi¬conducting Mg2Sn single crystals of different impurity concentrations were made between 2 and 30 microns at temperatures ranging from 18° to 296°K. At incident photon energies less than 0.22 ev, strong free-carrier absorption is present whose dependence on wavelength X can be approximated by a relation o=a + bλ2. where a is the absorption coefficient and a and b are constants. The absorption spectra due to other mechanisms has been analyzed after subtraction of the A free-carrier dependence. At energies of 0.22 ev and above, the rapid increase in absorption is attributed to the intrinsic edge. From the energy dependence of absorption in the edge region, the mechanism of indirect transitions between the valence and conduction bands can be established. The energy axis intercepts of the straight lines representing phonon emission decrease with temperature, indicating a negative temperature variation of the absorption edge.