Improvement in the quantum sensitivity of InAs/InAsSb/InAsSbP heterostructure photodiodes

InAs/InAs$_{0.88}$Sb$_{0.12}$/InAs$_{0.50}$Sb$_{0.20}$P$_{0.30}$ heterostructure photodiodes operating at room temperature in the spectral range 1–4.8 $\mu$m are developed. It is shown that the formation of a curvilinear reflecting surface constituted by a number of hemispheres on the rearside of the photodiode chip leads to an increase in the quantum sensitivity of the photodiodes by a factor of 1.5–1.7 at wavelengths in the range 2.2–4.8 $\mu$m. At an exposed photodiode area of 0.9 mm$^2$ and a $p$–$n$ junction area of 0.15 mm$^2$, a zero-bias differential resistance of 30 $\Omega$ and a quantum sensitivity of 0.24 electron/photon at a wavelength of 3 $\mu$m are obtained. The operation of a photodiode with re-reflection of the photon flux in the crystal due to reflection from the curvilinear surface of the rearside of the photodiode chip is theoretically analyzed. The possibility of effective conversion of the re-reflected flux of photons into a photocurrent, with a simultaneous decrease in the $p$–$n$ junction area, is demonstrated. An increase in the quantum sensitivity in the short-wavelength spectral range 1–2.2 $\mu$m by 35% relative to the calculated data is observed, which is probably due to impact ionization in the narrow-gap active region.