  Incorporating emerging ultrawide bandgap semiconductors with a
metal-semiconductor-metal (MSM) architecture is highly desired for
deep-ultraviolet (DUV) photodetection. However, synthesis-induced defects in
semiconductors complicate the rational design of MSM DUV photodetectors due to
their dual role as carrier donors and trap centers, leading to a commonly
observed trade-off between responsivity and response time. Here, we demonstrate
a simultaneous improvement of these two parameters in {\epsilon}-Ga2O3 MSM
photodetectors by establishing a low-defect diffusion barrier for directional
carrier transport. Specifically, using a micrometer thickness far exceeding its
effective light absorption depth, the {\epsilon}-Ga2O3 MSM photodetector
achieves over 18-fold enhancement of responsivity and simultaneous reduction of
the response time, which exhibits a state-of-the-art photo-to-dark current
ratio near 10^8, a superior responsivity of >1300 A/W, an ultrahigh detectivity
of >10^16 Jones and a decay time of 123 ms. Combined depth-profile
spectroscopic and microscopic analysis reveals the existence of a broad
defective region near the lattice-mismatched interface followed by a more
defect-free dark region, while the latter one serves as a diffusion barrier to
assist frontward carrier transport for substantially enhancing the
photodetector performance. This work reveals the critical role of the
semiconductor defect profile in tuning carrier transport for fabricating
high-performance MSM DUV photodetectors.
