Ultraflexible and Transparent MoS₂/β-Ga₂O₃ Heterojunction-Based Photodiode with Enhanced Photoresponse by Piezo-Phototronic Effect

Two-dimensional material-based flexible devices are extremely suitable for smart, portable, and wearable applications. However, the inevitability of substrate strain, which significantly affects device performance, makes it difficult to get a flexible device to function efficiently. Herein, for the first time, we report a flexible MoS 2 /β-Ga 2 O 3 broadband photodiode with an enhancement in the photocurrent and responsivity with bending. The electrical analysis of the heterojunction demonstrated excellent photoresponse characteristics with a photo-to-dark current ratio of 10 3, even at low power density. Compared to strain-free conditions, the device showed an enhancement in the photocurrent and responsivity by 155% and 136%. Based on the piezo-phototronic effect, the band structure at the heterojunction interface is modified by the piezo-potential caused by applied strain, which also widens the depletion region. The wider depletion can be employed discretely to increase photogenerated carrier separation and transport, improving photoresponse performance. The bending durability and robustness of the photodiode were also investigated at 500 bending cycles and high temperatures. The band alignment of the heterojunction was determined before fabricating the flexible photodiode. The junction showed straddling (type I) band alignment, with a valence band offset (Δ E V ) of 2.28 eV and a conduction band offset (Δ E C ) of 0.73 eV, as validated by first-principles calculations. This research paves the path for strain-tunable vdW heterojunctions, which might lead to the invention of flexible optoelectronic devices.