Optical properties of 1 by 16 highly sensitive InP/InGaAs heterojunction phototransistor arrays

We present the optical properties of a gain enhanced, highly sensitive, InP/InGaAs, heterojunction phototransistor (HPT) 1 by 16 array with two terminal configurations for near IR light detection. To increase optical gain and responsivity, the HPT's epitaxial layer structure was optimized as the collector doping reduced and the collector thickness increased. By placing the absorber in the collector depletion region of an HPT, the photogenerated current is electrically amplified, giving the device gain. The device exhibited significant optical responsivity of 280 A/W which is significantly higher than that of reported HPTs and conventional PIN photodetectors with the same light absorbing area. Although this device shows high optical gain and responsivity, the optical cut-off frequency of the HPT was measured to be 6.1 GHz, which is enough speed for most optical applications.