Thermal mismatch engineering induced freestanding and ultrathin Ga₂O₃ membrane for vertical electronics

Inevitable thermal-expansion-coefficient mismatch at the interface of epitaxial-layer/foreign-substrate is generally considered as a weak side since considerable strain would be induced during the temperature ramping process. However, rather than the conventional strain minimizing strategy, engineering this thermal-induced strain, i.e., beyond the tolerance of the interfacial bond energy, may result in the exfoliation of the epitaxial layer from bulk substrate. In this work, Ga₂O₃ membrane, a promising and desirable material for deep ultraviolet (DUV) photonics and high-power electronics, could be exfoliated from a pre-deposited Si-doped Ga₂O₃/AlN template in a high-temperature environment, allowing the vertical device configuration and preferable thermal management regardless of the costly Ga₂O₃ substrates. The exfoliated Ga₂O₃ membrane, which is comparable to the commercial Ga₂O₃ substrates, is freestanding, centimeter-scale, but ultrathin. The exfoliated Ga₂O₃ membrane was applied to a vertical DUV photodetector, which demonstrated an on/off ratio of 4.20 × 10⁴, responsivity of 170.3 A/W, and detectivity of 1.01 × 10¹³ Jones under 254 nm illumination at a bias of −5 V. The presented thermal mismatch engineering (TME) would allow researchers to look beyond the hetero-mismatch and unitize the interfacial strain for membrane exfoliation, e.g., freestanding Ga₂O₃ membrane for vertical electronics that avoid the ongoing high-cost native substrates.