I just want to explain the main idea. Let Ec and Ev be the conduction and
valence band energies in ideal QW (no fluctuations). Decrease of the
bandgap is proportional to the Indium concentration, while probability to
find such a fluctuation decrease exponentially. So we assume that
probability to find electrons with energy Ec-E and holes with energy Ev+E
drops exponentially with E. This conclusion is supported by various
experimental observations of low-energy tail of emission spectrum. In
SiLENSe, Un and Up are characteristic widths of the low energy tail in the
density of states (DOS) for electrons and holes, respectively. Below Mark
described how we set default values.


> The idea of the redistribution is very simple. First we determine the
> total U = Un + Up to be nearly equal to 50 meV, as follows from analysis
> of many emission spectra reported in literature (the range of U
> variation is typically 40-65 meV). Next we assume that U is distributed
> between the conduction and valence band in accordance to the offsets
> typical of III-nitride alloys: 70/30. This gives Un = 35 meV and Up = 15
> meV.
>