237InGaN-Based Solar Cells
incorporation of Al in barrier layers. The reduction in R
series
and the enhanced extrac-
tion efciency of photo-generated carriers from the active layer in devices with
AlGaN SLs were attributed to the increased polarization elds.
Besides, some of the studies have focused on the choice of the substrate for the
growth and the texturing of the surface to enhance the light absorption of the SC.
The most commonly used substrate is sapphire where InGaN growth is performed
on a GaN buffer layer on top of the substrate. Horng et al. [64] and Tsai et al. [65]
both reported exploiting the laser liftoff technique to remove the sapphire sub-
strate of the thin-lm p-i-n In
x
Ga
1−x
N /GaN SCs with In content of 10% and 8.5%,
respect ...