Sub-bandgap irradiation

This technique has been elaborated as an electrochemical tool by Tench and co-workers [164-166]. Its main purpose is to explore the deep-lying bulk and surface levels and the principle of the technique is that the main role of sub-bandgap irradiation in a semiconductor will be to cause optical excitation to or from a bulk or surface state this, in turn, will cause an alteration in the potential distribution from that existing in the dark this alteration will manifest itself in the behaviour of the interfacial capacitance. 

Figure 2.14 Local deformation of a GeSeg glass fiber subjected to torsion stress during local irradiation with sub-bandgap light (790 nm] at an intensity of 5.6 W/cm (after [32]].

Figure 2.16 Comparison ofphotoinduced and thermally induced relaxation in a series of Ge-As-Se glasses as a function of the mean coordination . Each irradiated sample was exposed to 3 W/ cm sub-bandgap light corresponding to the same absorption coefficient for each glass using a tunable laser. Annealed glasses were heat-treated for 80 hr at Tg 25°C (after [33]).

---