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 x 104, responsivity of 170.3 A/W, and detectivity of 1.01 x 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.