Quasi-3-dimensional simulations and experimental validation of surface leakage currents in high operating temperature type-II superlattice infrared detectors

Abstract

The surface leakage in InAs/GaSb type-II superlattice (T2SL) is studied experimentally and theoretically for photodiodes with small sizes down to 10 × 10 μm2. The dependence of dark current density on mesa size is studied at 110 and 200 K, and surface leakage is shown to impact both generation–recombination (GR) and diffusion dark current mechanisms. A quasi-3-dimensional model to simulate the fabrication process using surface traps on the pixel's sidewall is presented and is used to accurately represent the dark current of large and small pixels with surface leakage in the different temperature regimes. The simulations confirmed that the surface leakage current has a GR and diffusion component at low and high temperature, respectively. Finally, the surface leakage current has been correlated with the change in minority carrier concentration at the surface due to the presence of donor traps.

Two-step etch in n-on-p type-II superlattices for surface leakage reduction in mid-wave infrared megapixel detectors

“…For both regimes, the current density of the small pixel is higher than in the large pixel because of the increasing contribution of surface leakage current as pixel size decreases. The activation ener- gies of the surface leakage components are 𝐸 a,surf = 1/2𝐸 𝑔 , 𝐸 a,surf = 𝐸 𝑔 indicating that surface current densities in this case emanate from GR and diffusion mechanisms [13,14,20].…”

“…At higher temperature, the n-on-p devices show a GR activation energy as the minority carrier current dominates over surface drift current. The surface nature of both the GR-and the surface-drift mechanisms in these n-on-p diodes is the reason why the smaller pixel has a higher dark current density than larger pixels while the activation energies stay the same (𝐸 a,surf = 1/2𝐸 𝑔 , 𝐸 a,surf ≈ 0 𝑒𝑉 [13,14,16,19].…”

“…On the other hand, the etching process to isolate individual diodes of the array can cause an increase of the dark current density by adding surface leakage. Surface leakage can be described with a trap-assisted recombination density at the mesa edge of the device [13] and results in dark current activated by majority carrier drift, tunnelling, generation-recombination (GR), or diffusion [13,14]. For all these cases, the dark current degradation increases as the perimeter to the diode area ratio increases.…”

Simulation and Characterization of the Modulation Transfer Function in Fully Delineated Type-II Superlattices Infrared Detectors

“…The first one is related to the surface leakage current originating from the mesa sidewalls which can degrade the dark current density of small pixels [5]. The second is the loss of fill factor (in the case of delineated pixels), which can reduce the optical response of the array [6].…”