J. Eur. Opt. Society-Rapid Publ. 22, 39( 2026) 385
Figure 4.( a) Dark and photocurrent of the nBn-InGaAs structure with various barrier thickness,( b) dark current graph with different Al ratio.
Figure
5. Dark current components as a function of reverse bias voltage at 300 K.
configuration under strong reverse bias conditions and underscores its superior reliability compared to conventional pin InGaAs photodiodes [ 28 ], particularly in highvoltage and wide-dynamic-range applications. For comparison, conventional InGaAs pn photodiodes typically exhibit relatively low breakdown voltages due to the strong electric field concentration within the depletion region, which promotes early onset of avalanche multiplication through Impact Ionization. In such structures, the high doping gradients result in a narrow depletion width and consequently a large peak electric field, leading to breakdown at relatively low reverse biases. In contrast, nBn architectures eliminate the pn junction and instead rely on a unipolar barrier to control carrier transport. As a result, the electric field is more uniformly distributed across the device, significantly reducing the peak field intensity [ 29, 30 ].
Figure 6b shows that the device exhibits a capacitance of approximately 9.2 pF at �5 V bias and 1 kHz frequency, which can be attributed to the presence of the thick absorber layer. Such a low capacitance not only minimizes noise but also enhances temporal response and dynamic range, resulting in improved signal fidelity for high-speed and low-noise infrared detection [ 31 ]. These findings demonstrate that, beyond its dark-current suppression capability, the nBn-InGaAs architecture combines electrical stability with excellent frequency response, confirming its potential for next-generation infrared photodetector technologies.
After evaluating the electrical characteristics, the photoresponsivity performance of the device was examined. Prior to responsivity analysis, the optical reflection behavior of the InP substrate was characterized, revealing that approximately 30 % of the incident short-wavelength radiation is reflected from its surface. To enhance photon-to-electron conversion efficiency and improve overall responsivity, an anti-reflection( AR) coating was designed based on the reflectance formulation [ 32 ] equation( 1). Figure 7a compares the reflectance spectra of a bare InP surface with structures incorporating Si 3 N 4( 140 nm) and SiO 2( 150 nm) AR layers in the wavelength range of 0.8 – 1.7 lm. As illustrated, the AR-coated configuration significantly suppresses surface reflection, reducing it from nearly 30 % to approximately 0.02 % at 1.55 lm, which is expected to yield improved photocarrier generation and enhanced detector responsivity. Si 3 N 4 and SiO 2 were selected as AR materials due to their low extinction coefficients in the sub-2 lm band, making them well-suited for near-infrared photodetector applications [ 33 ].
r 1 ¼ n 0 � n 1 n 0 þ n 1
r 2 ¼ n 1 � n 2 n 1 þ n 2
r 3 ¼ n 2 � n 3 n 2 þ n 3
h 1 ¼ 2pn 1t 1 k ð1Þ
ð2Þ
ð3Þ
ð4Þ