The authors have experimentally investigated photoexcitation effects on carrier transports through a Ge quantum-dot (QD)/SiO2 system via a resonant tunneling diode (RTD). Features of resonant oscillation and negative differential conductance are observed from the tunneling current of Ge-QDs RTDs at room temperature. The tunneling current not only displays additional oscillatory peaks but also exhibits enhanced peak-to-valley current ratio under photoexcitation. This indicates that holes created in the QD by photoexcitation lead to additional channels via the electron-hole interaction for electron tunneling through the QD. The exciton binding energy in the Ge QD could also be extracted from the voltage separation of the tunneling current peaks.