Pinch-off driven near-ideal output characteristics of n-Ga₂O₃/p-GaN light effect transistor for UV photonics

Gallium oxide (Ga₂O₃) based phototransistor can be used as a switch and an amplifier in typical digital and analog UV photonic applications, respectively. The light detection capability in Ga₂O₃ is very high, but these phototransistors suffer from poor drain current saturation with bias. Furthermore, the transistor switching action generally necessitates a gate terminal voltage, where a faulty gate power supply can lead to a high current flow in the transistor and subsequently damage the control driver circuit. An alternative is a two-terminal device with pure optical coupling at gate terminal, termed as a light effect transistor (LET). The LET has the field effect transistor (FET)-like current-voltage output characteristics, where the controlling mode is light instead of voltage, and being a two-terminal device, the fabrication processes are straightforward and cost-effective in contrast to the traditional FET. The fabricated LET device comprised an n-Ga₂O₃/p-GaN heterojunction with a planar metal-semiconductor-metal structure. This unique device can operate in two modes, linear (photodetector) within 1-2.5 V and saturation [depletion width modulated light effect transistor (DM-LET)] within 2.5-5 V. Under the DM-LET mode, the structure exhibits transistor-like action, the drain current saturates with the variation in drain voltage and is only controlled by the change in optical intensity. The transistor-like action has been attributed to the pinch-off effect near the drain electrode due to modulation in the heterojunction depletion width and has been explained using detailed numerical simulation. Such devices have the potential to be used in UV photonic integrated circuits and UV-non-line-of-sight communication technologies.