2. Parameters for simulations
The expressions of InxGa1xN and AlxGa1xN alloys are listed in
Table 1 and the values of SnS, InxGa1xN and AlxGa1xN material
parameters used in the simulations are shown in Table 2. Absorption
coefficient a(k) of SnS thin film used in this paper is the
same as Ref. [34] and the minority electron lifetime is 0.8 ls
[37]. For n-InxGa1xN/p-SnS and n-AlxGa1xN/p-SnS heterojunction
solar cells, the minority electron lifetime strongly affects the
overall efficiency since most of the light absorption occurs in the
p-type layer. The electron and hole mobilities of SnS are 4.3 [37]
and 130 cm2 V1 s
1 [1], respectively. The electron mobility, along with
the minority electron lifetime, will determine the minority
electron diffusion length which in turns affects the device effi-
ciency. The surface recombination velocities are 2 104 cm s1 [37].
Constant bowing parameters 1.43 and 0.69 are used for the
band gaps of InxGa1xN and AlxGa1xN, respectively (see the
expressions of band gaps in Table 1). The formulae of the relative
permittivity and effective density of states in the conduction band
and valence band are obtained from the linear interpolation of the
corresponding parameters of InN and GaN. Absorption coefficient a
(k) of InxGa1xN and AlxGa1xN is the same as Ref. [38]. Hole lifetimes
as high as 6.5, 5.4 ns and 20 ns have been observed in GaN,
InN and AlN, respectively [39–41]. However, InxGa1xN and
AlxGa1xN alloys are likely to have lower lifetimes due to compositional
fluctuations, and therefore 1 ns minority hole lifetime was
assumed [25]. The electron and hole mobilities were calculated