High-Responsivity Deep-Ultraviolet-Selective Photodetectors Using Ultrathin Gallium Oxide Films

Abstract

Wavelength-selective photodetectors responding to deep-ultraviolet (DUV) wavelengths (λ = 200–300 nm) are drawing significant interest in diverse sensing applications, ranging from micrometer biological molecules to massive military missiles. However, most DUV photodetectors developed thus far have suffered from long response times, low sensitivity, and high processing temperatures, impeding their practical use. Here, we report fast, high-responsivity, and general-substrate-compatible DUV photodetectors based on ultrathin (3–50 nm) amorphous gallium oxide (GaOX) films grown by low-temperature (∼<250 °C) atomic layer deposition (ALD) for the first time. ALD-grown GaOX films on glass substrates display a typical amorphous nature, which is identified by electron beam diffraction and X-ray diffraction measurements, while their band gap is sharply featured at ∼4.8 eV. Metal–semiconductor–metal photodetectors (active area of 30 × 30 μm2) using the 30-nm-thick GaOX films work reliably only for DUV wavelengths; the responsivity is maximized to 45.11 A/W at λ = 253 nm, which dropped off at λ ≈ 300 nm (i.e., a cutoff wavelength). The dark current measured at 10 V is as low as 200 pA and the signal-to-noise ratio reaches up to ∼104, underpinning the pristine material quality of the ALD-grown GaOX films. In addition, the rise time (i.e., the time interval for photocurrent to increase from 10% to 90%) is as quick as 2.97 μs at λ = 266 nm. Such a reliable and fast photoresponse is achieved for even atomically thin (∼3 nm) devices. The substrate-compatible and low-temperature ALD growth permits the demonstration of flexible DUV photodetectors using amorphous GaOX films grown on polyimide substrates, suggesting their facile integration into other curved optoelectronic systems. We believe that photodetectors developed herein will provide an economically viable solution for high-performance DUV detection and create a variety of sensing applications.