Figure 1
Schematic illustration of the processes described in this work. Upon the absorption of a high-energy photon, an energetic e–h pair is created. (a) These electrons and holes can ‘cool down’ to the band edges in a multistep phonon emission process and can then be extracted in the form of electric current or can recombine either radiatively (emission of a photon with energy equal to the bandgap) or non-radiatively. (b) Alternatively, CM can occur, and the ‘excess’ energy is used to excite a second e–h pair (for simplicity, only electrons are shown, although both electrons and holes can take part in CM). This process can take place when the energy of the electron or the hole is larger than the bandgap. (c) The opposite process is Auger recombination, in which the electron recombines with the hole and the released energy is used to excite (a) carrier(s) further into the band. Because of the rapid occurrence of these two processes, one can imagine a superposition state, indicated by the feathered arrow. CB, conduction band; CM, carrier multiplication; e–h, electron–hole; VB, valence band.
