characteristic with a bandgap energy of ≈1.4 eV. The bandgap energy also enables its usage in visible photodetection. [7,8] In addition, GaAs has exhibited its potentials in the ultraviolet (UV) photodetection due to the high absorption coefficient. [9,10] Nowadays, broadband UV-visible photodetectors exhibit outstanding application potentials in areas such as environment, energy, and imaging. [11] Among various semiconductor materials, GaAs is one of the best candidates for broadband UV-visible photodetection considering the suitable bandgap for visible light detection and high absorption coefficient in UV range.However, two challenges still exist in improving the UV-visible responsivity of GaAs photodetectors: 1) surface reflection loss of incident light and 2) shallow penetration depth of GaAs in UV range. The former issue can be effectively ameliorated by employing various antireflection schemes. Among them, surface texturing such as textured GaAs, [12,13] GaAs nanocones [14,15] and porous GaAs [16][17][18][19] has shown a facile and effective way to achieve a broadband antireflection, compared with a multilayered antireflection coating which requires a precise control of refractive index and thickness of individual layer. [20] Although some of these works on surface texturing demonstrated low UV-visible reflection below 5%, none of them have systematically studied an implication of the textured antireflection layer in GaAs photodetectors and their performance enhancement in a broadband UV-visible range. For example, Namiki et al. [21] fabricated GaAs nanogrooves which exhibited distinctly reduced reflectance from 400 to 1000 nm wavelength. However, this photodetector was only characterized under 532 nm visible illumination and its performance enhancement in a broadband UV-visible range was not reported. In fact, it is challenging to realize the UV performance enhancement in GaAs photodetectors due to the latter issue, i.e., the shallow penetration depth of UV light in GaAs which leads to significant loss of photocarriers by recombination. [22] The surface recombination is expected to be more severe in UV range for antireflective structures due to potential formation of more surface states as traps and recombination centers which are introduced by larger surface areas and fabrication methods such as etching. [12,23] On the other hand, Broadband ultraviolet-visible photodetection has been attracting growing research interests in fields of environment, energy, and imaging. Considering the suitable bandgap and high absorption coefficient, GaAs is one of the best candidates for ultraviolet-visible photodetection. In this work, a monolithic integration strategy of nanopillar antireflective structure and InGaZnO (IGZO) ultraviolet absorbing layer is proposed to enhance the ultraviolet-visible spectral responsivity of GaAs photodetectors. Both nanopillar topography and IGZO layer exhibit antireflective performance, leading to the enhancement of the light absorption and responsivity of the photodetectors. By the comb...
