PNP pin phototransistor with modulation-doped base

A p⁺np^-p⁺ phototransistor implementing a modulation-doped base is presented. To increase the responsivity for red and near-infrared light, the collector of the device is formed by a thick low-doped p^- region. This leads to responsivity values of up to 12, 37, 47, 50, and 40A/W at wavelengths of 400, 550, 660, 770, and 850 nm, respectively. A detector with a light-sensitive area of 50 μm square reaches a -3 dB bandwidth of 4.3 MHz at 675 nm and 3 V collector-emitter voltage.