Design and modelling of high-operating temperature MWIR HgCdTe nBn detector with n- and p-type barriers

The paper present the numerical analysis of the electrical and optical properties of the mid-wave infrared (MWIR) HgCdTe nBn type detectors with a 3.4 μm cut-off wavelength (at 50% of the initial rise in the response) operating at 230 K. The analysed n⁺/B/n/N⁺ structure consists of four HgCdTe layers with n- and p-type barriers. Different structural parameters, as well as compositional and dopant profiles obtained in molecular beam epitaxy (MBE) and metal organic chemical vapour deposition (MOCVD) techniques were modelled with emphasis on conduction band and valence band-offset which determines the proper construction of the nBn type devices. The barrier must prevent the flow of the electron current from the cap region to the absorber while simultaneously ensure the flow and collection of thermally and optically generated holes from the absorber to the cap region. It was shown that proper p-type doping of the barrier reduce the valence band-offset and increase the offset in the conduction band leading to the optimal detector architecture.Theoretical results were related to the experimental data of the MWIR n⁺/B/n/N⁺ photodetectors grown by MOCVD. Dark currents of the first fabricated devices are limited by undesirable iodine diffusion from cap layer to the barrier. However, the nBn architecture might be a promising solution for HgCdTe infrared detectors grown by MOCVD, mainly due to the possibility of in situ acceptor doping of the barrier.