# Improvement of Porous GaN-Based UV Photodetector with Graphene Cladding
## 1 Introduction  
Graphene is best described as a single layer of carbon atoms arranged hexagonally on a flat two-dimensional (2D) plane. It is also known as a zero-gap material with excellent electronic and thermal properties [1, 2, 3]. Several known methods such as chemical vapour deposition (CVD), electrochemical exfoliation (EC), Hummers, and so on have gained interest in the scientific community for graphene production [4, 5, 6, 7, 8, 9, 10, 11]. Graphene films of lower defects and thickness of monolayers can be grown on copper substrate using the CVD method [12, 13, 10, 11]. This method employs vacuum furnace and flow meters, as well as hydrocarbon precursors (e.g., methane) and hydrogen, in order to facilitate the necessary chemical reactions. The aforementioned reactions ascribed to the decomposition of vapour phase hydrocarbons under hot (\(\sim\)1000 \({}^{\circ}\)C) and reducing (hydrogen) environment subsequently condensed on the copper surface, which catalyses graphene growth. Given the costly production, other alternatives have been explored as well. The EC methods operate through the insertion of chemical ions between graphene layers within a graphitic structure. This mechanism is also known as intercalation. Ions of larger size such as SO\({}_{4}\)\({}^{2-}\) would be suitable to be intercalated between graphene layers,which leads to structural expansion. Consequently, this weakens the van der Waals forces between graphene layers, making them easier to exfoliate. The exfoliation can be performed using various methods, including microwave, sonication, and so on. With optimization, micron-sized graphene flakes can be obtained [3, 14, 15]. Gallium nitride (GaN) belonged to the family of group III-nitrides. GaN, a type of semiconductor with a direct bandgap of 3.4 eV, is essential in optoelectronics applications such as light-emitting diodes (LEDs) and ultraviolet (UV) photodetectors (PDs) [16, 17, 18]. In recent years, nanostructured GaN has gained popularity in terms of producing more sensitive and efficient devices with higher surface-area-to-volume ratios. One of the known nanostructured GaAs is porous GaN, which is obtained through UV-assisted photoelectrochemical etching (PEC) of thin-film GaN [19, 20]. The PEC of GaN can be achieved with or without biasing potential under either acidic or alkaline medium, provided the sample was kept illuminated with a UV light source. Among the options, the presence of biasing potential ensured the uniform etching of GaN. In either acidic or alkaline medium, the etching commenced preferably in the doped region, where the resistance was low. As a result, the post etched region would be highly resistive; however, this feature can be exploited in the fabrication of sensors [21]. Photodetectors (PDs) in general are important components in various optical systems ranging from medical to military applications [22, 23, 24, 25]. PDs in general can be categorized into two groups based on their operating mode, i.e., photovoltaic and photoconductive mode [22]. One major difference is the necessity of external bias, where the former is self-operating, while the latter requires an external bias for better charge transport. It is noteworthy that photovoltaic PDs have great importance in sustainability as they self-operate, with one notable work from [PERSON] et al., investigating the performance of MXene/GaN UV PDs [26]. On the other hand, photoconductive PDs are equally important in other sectors. While a variety of PDs has been produced annually, there is still ongoing research on further improving their performance. Under demanding situations, a good PD should be able to operate with high speed, responses, sensitive, stable, and well-defined bandwidth. These criteria, however, are highly influenced by the surroundings and the sensing material. One particular example is PDs operating at the UV range, where constant illumination from such a wavelength would induce localized heating, potentially affecting the PDs' sensitivity [27].