## 3 Results
### Dark Current-Voltage and Capacitance-Voltage Measurements  
Figure 7 shows typical J-V characteristics carried out for a 210 \(\upmu\)m diameter detector in the temperature range (120-270 K). At the 150 K targeted temperature operation, dark current density as low as 3.5 \(\times\) 10\({}^{-5}\) A/cm\({}^{2}\) is recorded. Such a result must be improved, since when compared to the MCT state-of-the-art photodiode limited by diffusion dark current [36], the current is 20 times higher at the corresponding cut-off wavelength. Nevertheless, this value remains in agreement with the most recent results reported on Ga-free T2 SL detectors [14; 15; 17; 18; 19; 20; 21]. From the dark J-V characteristics, transport regimes in the barrier detector can be identified by plotting the dynamic resistance area product R\({}_{\mathrm{d}}\)A = (\(\mathrm{\delta J}/\mathrm{\delta V}\))\({}^{-1}\), where A is the area of the device (210 \(\upmu\)m diameter). Through the shape of the displayed curves in Figure 8, we can identify the main dark current regimes and analyze the QE spectra recorded (Figure 5). Figure 6: Quantum efficiency measured at \(\lambda\) = 3.4 \(\upmu\)m as a function of the applied bias voltages for various detectors’ temperatures. The first significant bias value is the turn-on voltage (Von). This bias is located at the first R\({}_{\rm d}\)A minimum and its value decreases when the temperature increases, from 260 mV to 85 mV in the temperature range (130-210 K). Below Von, the minority carriers are blocked due to the presence of the VBO in addition to the possible potential barrier due to the difference in doping between AL and CL. Above the reverse bias Von, the minority carriers can flow unimpeded through the barrier detector, and the quantum efficiency value decreases. Figure 8: Differential resistance area (R\({}_{\rm d}\)A) product as a function of the voltage for various detectors’ temperature. Positions of relevant voltages (Von, Vop, V\({}_{\rm GR}\)) are identified (dotted line). Figure 7: Dark current density characteristics of XBn InAs/InAsSb T2 SL detector at different temperatures from 120 K to 270 K.  
becomes higher than 80% of its maximum value (Figure 6). We can remark that the higher the temperature, the lower the required voltage. Next, the device reaches the operating voltage Vop. It is defined as the bias at which the maximum R\({}_{\rm d}\)A product is obtained and is linked to the photoresponse spectra. At this particular Vop bias, the photonic current/quantum efficiency begins to saturate (Figure 6). At the targeted temperature of 150 K, Vop = \(-\)400 mV and the corresponding R\({}_{\rm d}\)A product is equal to 2.5 \(\times\) 10\({}^{\rm f}\)\(\Omega\).cm\({}^{2}\) (Figure 8). Then, over Vop, the next visible R\({}_{\rm d}\)A minimum V\({}_{\rm GR}\) indicates the beginning of the generation-recombination (GR) regime. At this bias, the barrier is fully depleted and the depletion region expands into the absorber, which explains the appearance of the electric field-related GR current. Such behavior is only observed at low temperature since the device is diffusion current-limited for temperatures higher than 170 K.  
Finally, extracted from J-V curves of Figure 7, dark current densities at Vop = \(-\)400 mV are reported as a function of 1/k\({}_{\rm B}\)T (Arrhenius plot) in Figure 9, where k\({}_{\rm B}\) is the Boltzmann constant. A fit over the temperature range (150-270 K) using the expression A exp(-E\({}_{\rm a}\)/k\({}_{\rm B}\) T) yields an activation energy E\({}_{\rm a}\) = 230 meV, which is approximately the T2 SL energy bandgap (E\({}_{\rm g}\)) in this temperature range, signature of a diffusion-limited behavior. In the temperature range (120-150 K), the activation energy is 117 meV, approximately one half of the T2 SL bandgap (E\({}_{\rm g}\)/2), indicating that the dark current is GR-limited, due to the presence of a depletion region extending into the AL.