Toward high-efficiency near-infrared Ge-on-Si photodetectors at normal incidence, a trench-filling epitaxy to form a micron-thick Ge is presented. The key technology is to use a patterned (001) Si substrate with an array of submicron-wide trenches in the <100> direction, deviating from the ordinary <110> direction. Chemical vapor deposition with a GeH₄ source gas in a molecular flux regime allows Ge to grow not only on the trench bottom but also on the {010} trench sidewalls. The sidewall growth significantly shortens the growth time for a micron-thick Ge by the trench-filling compared to a planar growth.