Ionization energies in Cd_xHg_1-xTe avalanche photodiodes

Abstract

The CdxHg1-xTe avalanche photodiodes present hole or electron majority multiplication, depending on the x values, with a ratio of ionization factors k= alpha h/ alpha e maximum for x=0.6 and minimum for x=0.4. This behaviour is explained by a simulation of the multiplication phenomenon. Monte Carlo electron trajectories are averaged to obtain ionization factors alpha h and alpha e. This model introduces a linear relationship between the logarithm of k and the ionization energy difference for holes and electrons: Delta Ei=Eih-Eie. The authors compute this energy difference in an empirical tight binding band structure and show that its variation versus x agrees with experimental k(x) variations. The hole multiplication maximum at x=0.6 is explained as the effect of transitions issued from the split-off band at Gamma .