## 4 Discussion  
For the \(nBn\) device, the QE values were lower but close enough to those for the mesa-isolated diodes. For the \(pBn\) design, on the other hand, the gap in QE values was higher compared to the mesa-isolated devices. The reason for the effect is still unknown, but there was a speculation that it might be associated with the optical contribution of the sloped mesa sidewalls (mirror effect) to increase the QE a bit. There was also a difference  
Figure 6: \(D^{\bullet}\) spectrum at (**a**) 77 K and (**b**) 150 K for planar and mesa-isolated MWIR SLS devices ( diodes with 200 μm diameter). The \(D^{\bullet}\) values were calculated using the equation in the inset, where \(k_{b}\) is the Boltzmann constant, \(T\) is the operating temperature, \(J\) is the dark current, and \(R\times A\) is the resistance area product.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Design**} & \multirow{2}{*}{**Fabrication Approach**} & \(D^{\bullet}\) **@ 150 K** & \(D^{\bullet}\) **@ 77 K** \\  & & cm-Hz\({}^{12}\)/W** & **cm-Hz\({}^{12}\)/W** \\ \hline \(nBn\) & Mesa & \(1.86\times 10^{11}\) & \(1.52\times 10^{12}\) \\ \(\lambda=3.35\) μm & Planar & \(8.54\times 10^{10}\) & \(9.12\times 10^{11}\) \\ \(pBn\) & Mesa & \(3.37\times 10^{10}\) & \(1.52\times 10^{12}\) \\ \(\lambda=3.80\) μm & Planar & \(4.95\times 10^{11}\) & \(1.10\times 10^{12}\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Comparison of the \(D^{\bullet}\) values for planar and mesa-etched SLS devices at 77 and 150 K. (\(V_{\text{b}}=-40\) mV for \(pBn\) and \(V_{\text{b}}=-80\) mV for \(nBn\)).  
in QE values at 77 K and 150 K for each device, which is related to the limitation of n-type absorbers of Ga-free (InAs/InAsSb) SLS material, due to lower hole mobility values at lower temperatures.  
It has been reported that Ga free n-type absorbers deliver lower QE in general, due to shorter hole diffusion lengths and modest absorption coefficients [12; 34; 35]. The lower QE values at lower temperatures is also suspected to be electrically related to recombination occurring in the ion-implanted region at the periphery of the device at different temperatures. This hypothesis should be confirmed by a more detailed study on the temperature dependence of dark current.  
The uniformity level of the optical performances of the SLS planar devices was evaluated for optimized implantation parameters to make sure of the proper diode isolation by the implantation technique. To do so, the optical test was performed on different diode sizes at different temperatures, and it was confirmed that the QE values did not change across the different range of diode sizes. This is promising for focal plane array applications, which entails the scalability of the suggested method. It is worth noting that lower ion implantation energy can cause partial isolation, meaning that the energy is not strong enough to penetrate deeply into the substrate to pass the barrier (i.e., not reaching to absorption region) and generate isolated diodes. This means that the signal could come from the large area of the active region under the surface (much larger than the actual size of the diode), contributing to the responsivity, which causes inaccurate and large optical responses (e.g., QE > 100%). To evaluate this explanation, further simulations and empirical data are needed, which can be considered for the future direction of the study.