Silicon detectors have a limited hard X- and gamma-rays quantum-yield, mostly, devices fabricated in dedicated CMOS process for consumer electronics, where the sensitive volume is formed by the depletion region of a pn-junction of few or fractions of microns. This work reports on a Monte Carlo approach based on the PENELOPE code, to analyze the quantum yield-enhancement of high-Z coatings for Silicon detectors. The performance of different materials has been studied by simulation obtaining that the gadolinium dioxide produces the maximum efficiency of 3% for photons with energy over 50 keV.