  This work studies the effect of four different types of buffer layers on the
structural and optical properties of InGaN layers grown on Si(111) substrates
and their correlation with electrical characteristics. The vertical electrical
conduction of n-InGaN/buffer-layer/p-Si heterostructures, with In composition
near 46%, which theoretically produces an alignment of the bands, is analyzed.
Droplet elimination by radical-beam irradiation was successfully applied to
grow high quality InGaN films on Si substrates for the first time. Among
several buffer choices, an AlN buffer layer with a thickness above 24 nm
improves the structural and optical quality of the InGaN epilayer while keeping
a top to bottom ohmic behavior. These results will allow fabricating
double-junction InGaN/Si solar cells without the need of tunnel junctions
between the two sub-cells, therefore simplifying the device design.
