Assessing performance metrics via a

Assessing performance metrics via a photo-inverter. Key performance metrics54, such as photoresponsivity (Supplementary Note 1), noise-equivalent power, specific detectivity (Supplementary Note 5, Supplementary Fig. 18 and Supplementary Table 3) and response time (Supplementary Note 6 and Supplementary Fig. 19) are traditionally defined for photodiodes. Since phototransistors combine detection and amplification into a single device, it is more informative to consider their utility as a circuit element. Here we propose a simple circuit route that uses a photoinverter (Fig. 6a) to assess a phototransistor’s performance metric in a manner more applicable for optoelectronic circuit design. To demonstrate this concept, a PMOS-like photo-inverter served as a common-source amplifier was fabricated using two identical FACs HJPTs, where HJPT-1 and HJPT-2 respectively, were employed as the depletion load and electrical switch controlled by the input voltage signal (VIN). In this unipolar configuration, one can directly evaluate the intrinsic amplification (Ai) of the optoelectronic components (e.g. HJPT-1 and HJPT-2) for amplifying input signals55 as the latter is the main advantage for using an active electronic component like phototransistors. Moreover, Ai is an important criterion to separate a phototransistor from a photoconductor as a high Ai requires the saturation of ID (Supplementary Note 7 and Supplementary Fig. 20).