## 1 Introduction  
Because of the large bandgaps of GaN-based semiconductors, they have been widely used for developing ultraviolet (UV) detectors during the last decades [1, 2]. However, single-color detectors are gradually becoming unable to meet the application requirements of achieving a higher target identification performance and reducing the false alarm rate. In recent years, ultraviolet and infrared (UV-IR) dual-color photodetectors have gained a lot of interest for their promising applications in many fields, such as target recognition, space research, and fire detection [3, 4]. Detecting ultraviolet and infrared signals with a single device also has the advantages of having a low cost, easy operation, and robustness [5, 6]. Up until now, several types of GaN-based UV-IR dual-color photodetectors have been demonstrated. Ultraviolet/near-infrared (UV-NIR) and ultraviolet/long-wave infrared (UV-LWIR) dual-color photodetectors have been achieved using a Si/GaN/AlGaN heterostructure and GaN/AlGaN heterostructure, respectively [7, 8]. [PERSON] et al. proposed a monolithtically integrated ultraviolet and short-wave infrared (UV-SWIR) dual-color photodetector [9]. The device structure consists of an AlGaN thin film for UV detection and a 40-periods AlN/GaN superlattice for SWIR detection. However, the complex device structure and costly preparation process hinder the application of the UV-SWIR dual-color photodetector.  
These limitations mentioned above can be overcome through the photoelectric detection process based on hot electrons. When photon energy is smaller than the work function of metal, photons incident on a metal surface can excite electrons from occupied energy levels below the Fermi energy into energy levels above the Fermi energy, generating hot electrons. The typical hot-electron photodetection process is based on a metal-semiconductor Schottky junction. The hot electrons photon-excited in metal can cross the Schottky barrier and contribute to the photocurrent with a high probability when their energies are higher than the Schottky barrier height (SBH) [10]. The detection wavelength is related to SBH instead of the bandgap energy of the semiconductor material. Therefore, the hot-electron photodetectors can release the reliance of the working wavelength on the band structure of semiconductor materials [11; 12]. Moreover, the device structure and preparation process are simple, and there is a relatively wide choice of metals to construct Schottky barriers for photodetection [13]. In recent years, studies [14; 15; 16; 17; 18; 19] have mainly focused on using hot-electron photodetection to expand the detection wavelength of Si, with energy well below the bandgap of the Si. A Si-based hot-electron photodetector can operate in an infrared regime, but it is difficult to realize the UV detection based on Si. Yet, to the best of our knowledge, GaN-based hot-electron photodetectors are rarely reported.  
In this paper, we have designed and fabricated a hot-electron photodetector based on Au/GaN-nanopillar arrays, which is capable of photodetection at wavelengths in the SWIR range. A suitable SBH has been developed for higher photo-to-dark current ratios by post-etching annealing. The surface plasmons generated by Au/GaN-nanopillar arrays can effectively improve the light absorption efficiency. Compared with the planar device, the responsivity of the Au/GaN-nanopillar device in the SWIR range can be enhanced by about two orders of magnitude. The proposed devices can achieve low-cost fabrication and have a promising potential application in UV-IR dual-color photodetection.