EBIC Characterization of Vertical Transport of Minority Carriers in Gallium-Free Type-II Superlattices for Infrared Detectors

Abstract InAs/InAsSb type-II superlattices (T2SLs) are emerging as alternatives to HgCdTe for infrared detection, but their anisotropic hole transport could be a limitation in small-pitch focal plane array (FPA) detectors. To quantitatively assess this anisotropy in the device, modulated electron beam induced current (AC-EBIC) is performed on deep-etched mid-wave infrared (MWIR) T2SL photodiodes. Analysis of the EBIC amplitude and phase profiles reveals a transport anisotropy of 2.5 between lateral and vertical diffusion lengths. A numerical diffusion model fits the data, yielding diffusion lengths (3–4 μm vertically, 7–10 μm laterally), minority carrier lifetime (400–670 ns), and surface recombination velocity (< 800 cm/s). While AC-EBIC effectively quantifies transport anisotropy, current frequency constraints limit the decoupling of individual parameters. Nevertheless, beyond surface characterization, this study demonstrates AC-EBIC’s potential to resolve anisotropic diffusion parameters in photodiodes structures.