The mechanism of the photoresponse blueshifts for the $n$-type conversion region of $n+$-on-$p$ $Hg0.722Cd0.278Te$ infrared photodiode

The photoresponse blueshift of the $n$-type conversion region for $n+$-on-$p$ $Hg0.722Cd0.278Te$ infrared photodiode is numerically investigated by considering the conduction band nonparabolic characteristic and band gap narrowing effect. It has been shown that the photoresponse position of the $n$-type conversion region shifts remarkably toward high energy. The shift energy is 37 meV higher than that of the $p$ region. The result can be used to explain quantitatively the recent experimental observation of the blueshift of the photoluminescence peak for the $n$-type conversion region. The following three contributions are considered: (i) the Burstein–Moss shift considering a nonparabolic conduction band, (ii) the band gap narrowing effect, and (iii) the Hg-vacancy-induced acceptor trap level. It is concluded that the band gap narrowing and nonparabolic effects play an important role in the photoresponse of $n+$-on-$p$ HgCdTe infrared photodiode with heavy doping concentration.