## 1 Introduction  
Type-II strained-layer superlattice (SLS)-based photodetectors are of great interest as a new material system for infrared photodetectors and imaging systems. Recently, significant development has been made in the design, structure, and performance of SLS photodetectors as new alternatives for infrared detector material, beside to the industrially mature HgCdTe (MCT) material system [1; 2; 3; 4]. MCT is II-VI semiconductor alloy grown on nearly lattice-matched CdZnTe (CZT) substrate with strong optical absorption, delivering high performance infrared photodetectors with high quantum efficiency (QE), low dark current, and high operating temperature (HOT) capability, covering almost all infrared wavelength detection [3; 4]. However, MCT bears some drawbacks such as bulk and surface growth instability, low yields, and higher costs [1; 5]. SLS material on the other hand offers flexible band gap engineering covering a broad range of cutoff wavelengths along with reliable growth uniformity, high yield, and easier manufacturability [6; 7; 8; 9; 10; 11]. Compared to SLS-based infrared detectors, MCT is a front runner, delivering superior performance of QE and dark current. However, thanks to the recent progress in design and growth of unipolar barrier infrared photodetector architecture [12; 13], SLS is on the path of development for high-performance infrared photodetectors with reduced imaging system size, weight, and power consumption (SWaP) for focal plane array (FPA) cameras. Almost all the current SLS-based FPAs are fabricated by the mesa-isolated pixel approach. The deep mesa etch requirement to isolate the pixels is a major limiting factor due to fabrication challenges for small pixel pitch FPAs, along with the immediate need to passivate the long and exposed mesa sidewalls. Passivation is another challenge that needs to be addressed efficiently for small pixel pitch FPAs where the larger perimeter/area ratio can make the leakage current to play a critical contribution to the dark current density. Ample efforts have been made in developing applicable passivation methods to circumvent the surface leakage in narrow band gap SLS photodetectors. To address the issue, planar structures with buried junction interfaces and no passivation requirements have been proposed. The planar architecture itself has been implemented for a variety of materials, including MCT. Multiple designs and structures have been reported for planar MCT and InGaAs photodetectors [14; 15; 16] and for MCT-based FPA production [17; 18]. Diffusion and ion implantation are the most applicable methods of junction generation for p-n junction generation in planar devices. Recently for SLS photodetectors, planar structures made by avoiding the entire mesa-etching step and fabricated by diffusion and ion implantation techniques, have been proposed [19; 20; 21; 22]. However, given the specific epitaxial growth condition and the structure of SLS material, doping with diffusion or ion-implantation along with relevant annealing treatments can have a dramatic impact on elegant superlattice interfaces and can drastically degrade the material. In the case of ion-implantation, there is an alternative that, instead of doping the material, it attempts to perform ion-bombardment on epitaxially-grown doped layers to selectively create highly resistive regions with damage-related deep levels [23; 24; 25]. This highly-resistive area blocks the electrical crosstalk between neighbor detectors and achieves the same function as mesa isolation. Based on the ion-implantation for photodetector isolation approach, this work studied a comparison of the performance of mid-wavelength infrared (MWIR) heterostructure planar SLS photodetectors. Two planar devices with unipolar barrier structures were studied, as n-contact-Barrier-n-contact (\(nBn\)) and p-contact-Barrier-n-contact (\(pBu\)).