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J. Eur. Opt. Society-Rapid Publ. 22, 39( 2026)
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2. Simulated energy band diagrams of the nBn InGaAs structure for different Al compositions:( a) under equilibrium conditions and( b) under �150 mV reverse bias voltage.
Figure 3. Energy band diagrams of the nBn InGaAs structure under a 150 mV reverse bias for different N-type doping concentrations in the AlGaAs barrier.
commensurate benefit in dark-current suppression. Thus, to optimize the trade-off between dark-current reduction and photo-response, the barrier thickness in the nBn-InGaAs structure was selected as 100 nm [ 6 ]. In Figure 4b, asensitivity analysis was performed to evaluate the impact of band alignment uncertainties by varying the Al composition in the Al x Ga 1-x As( x = 0.55 – 0.59) 100 nm barrier. The results show that variations in Al content do not produce significant changes in dark current characteristics, indicating a weak dependence of device performance on moderate fluctuations in CBO and VBO. These findings confirm the robustness of the proposed nBn-InGaAs design against variations in material composition and the associated band offset uncertainties.
As illustrated in Figure 4a, the nBn-InGaAs structure exhibits a significantly lower dark current compared to conventional mesa and planar InGaAs photodiodes [ 22, 23 ], while maintaining nearly the same photocurrent magnitude. Furthermore, the photocurrent characteristics presented in Figure 4a were obtained under back-illuminated operation with an incident optical power density of 0.1 W / cm 2.
Figure 5 presents the decomposition of the dark current components as a function of reverse bias, providing insight into the dominant transport mechanisms in the proposed device. The total dark current( SUM) increases from approximately 3 10 �14 Aat0Vtoabout1 10 �10 A at 1 V, exhibiting a gradual bias-dependent increase. Among the individual components, the SRH generation current dominates in the low-to-moderate bias range, indicating that generation – recombination processes are the primary contributor to the dark current [ 24, 25 ].
In contrast, the tunneling current increases with reverse bias and becomes comparable to the SRH current at higher voltages, while remaining slightly lower overall, confirming that field-assisted leakage is effectively controlled by the barrier design. The diffusion current is nearly bias-independent and negligible in magnitude, suggesting minimal thermally driven carrier injection. Overall, these results demonstrate that the AlGaAs barrier effectively suppresses diffusion-related leakage, while the dark current is primarily governed by SRH generation at low bias and increasingly influenced by tunneling mechanisms at higher bias [ 26, 27 ]. These results confirm that the optimized barrier design effectively minimizes leakage pathways without compromising carrier collection efficiency, demonstrating the superior dark-current suppression capability of the nBn structure.
Following the analysis of the photocurrent characteristics, the simulated nBn-InGaAs structure was further evaluated in terms of its breakdown voltage and capacitance behavior, as presented in Figure 6. The results in Figure 6a show that the diode enters breakdown at approximately �82.5 V, primarily due to the combined effect of the thick absorber and barrier layers. This relatively high breakdown voltage highlights the structural robustness of the nBn