Geometry-defined impact ionization in two-stage mesa-type silicon electron multipliers

We demonstrate a silicon electron multiplier that achieves internal multiplication by impact ionization in a localized high-field region without relying on a dedicated doped gain layer. Two-stage mesa-type architecture induces strong electric-field crowding in a confined cylindrical mesa, thereby localizing the peak electric field within the mesa. The fabricated devices exhibit an effective multiplication factor (M) exceeding 100 for |Vgate| < 50 V. The buried gate electrostatically controls carrier transport through the injection stage into the multiplication stage (cylindrical mesa), enabling stable and tunable multiplication. Carrier transport is characterized by a pseudo-pinch-off condition that steers carriers toward the mesa’s center. The multiplication exhibits low temperature sensitivity of dVgate/dT = 24–30 mV/°C at constant M (M = 10). These results provide a design principle for geometry-defined electron multiplication with electrostatically controlled injection, particularly for semiconductors where conventional doped gain layers are impractical.