IONIZATION ENERGIES IN CDXHG1-XTE AVALANCHE PHOTODIODES

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: DELTAE(i) = E(ih) - E(ie). We 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.