Vertical GaAs p–i–n photodetectors epitaxially grown on GaAs(001), Ge/Si(001), and Si(001) substrates are reported. The performances of such photodetectors were investigated as a function of threading dislocation density in the stacks. A low dark current at room temperature, below 100 pA up to −9 V for all photodetectors, was evidenced. The absorption coefficients of GaAs were extracted from the spectral response of those p–i–n structures between 400 nm and 1100 nm. A responsivity of 0.17 A/W at 850 nm was obtained for a GaAs p–i–n structure grown directly on Si as compared to the value of 0.23 A/W obtained for the GaAs substrate. Such responsivity shows that III–V integration on Si is an efficient way of fabricating high performance optical sensors with low cost large scale productivity.
