A semiconductor is illuminated by light at 850 nm with 500 W/m2 at a right angle to the semiconductor surface. The refractive index and the absorption coefficient at 850 nm of this semiconductor are 2.80 and 80.0/cm, respectively. 

1. 1) How much percentage of the incident light is reflected?
2. 2) Assuming the rear side is non-reflecting, how much is the minimum thickness required to absorb >85% of the light which is not reflected at the semiconductor surface?