Distinct UV–Visible Responsivity Enhancement of GaAs Photodetectors via Monolithic Integration of Antireflective Nanopillar Structure and UV Absorbing IGZO Layer

Abstract

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...

Antireflective GaN Nanoridge Texturing by Metal-Assisted Chemical Etching via a Thermally Dewetted Pt Catalyst Network for Highly Responsive Ultraviolet Photodiodes

“…By a linear fitting as shown in Figure 4e, θ is extracted to be 1.62 and 0.73 for the PDs made on nanoridge and planar GaN, respectively. This indicates the photocurrent gain mechanism in the GaN nanoridge PD, 56,60 which is due to the barrier height lowering by photogenerated holes trapped at the metal−semiconductor interface. 61,62 Table 2 shows the benchmarking of our device with other reported GaN-based UV PDs.…”

“…The light absorption at 250 nm UV irradiation is limited to the top surface, causing weaker responsivity via local recombination of photogenerated carriers as well as surface recombination by surface states. 56 The slightly lower responsivity of the nanoridge GaN PD at 250 nm than the planar one is also an indicator of surface recombination since MacEtch has introduced certain surface states as suggested by PL results.…”

“…The FDTD simulated reflectance spectra of both nanoridge models with different tip dimensions (Figure 3c,d) are given in Figure S7. For the planar GaN, the out-ofplane periodic electric field is due to the constructive and destructive interference of the incident and reflective light, 56 with the electric field inside GaN remaining low intensity (blue/cyan color). For the nanoridge GaN, the enhanced electric field intensity is observed within the nanoridge structure, especially in the tip regions (green/yellow color).…”

“…We have extracted key parameters [e.g., responsivity ( R ), detectivity ( D *), and external quantum efficiency (EQE)] of the PDs based on the current–voltage characteristics of PDs in Figure b using the following equations R = I normalp normalh normalo normalt normalo − I normald normala normalr normalk P λ normalS D * = S R 2 q I normald normala normalr normalk normalE normalQ normalE = R h c / λ q where I photo and I dark are the photocurrent and the dark current, respectively, p λ is the incident light intensity (46 mW/cm 2 ), and S is the effective illumination area on the PD. q , h, c , and λ are the elementary charge, the Planck constant, the speed of light, and the wavelength of incident light (365 nm), respectively.…”

“…Therefore, it leads to an overall 6–8 times enhancement in sensing capability by using the GaN nanoridge structure. Figure e shows the incident power intensity-dependent photocurrents fitted by the power law as the following, with measured I–V plots shown in Figure S11 I normalp normalh normalo normalt normalo = C P λ θ where C is a constant and θ is the empirical coefficient. By a linear fitting as shown in Figure e, θ is extracted to be 1.62 and 0.73 for the PDs made on nanoridge and planar GaN, respectively.…”