Effect of low-temperature annealing on the quality of InSe layered single crystals and the characteristics of $n$-InSe/$p$-InSe heterojunctions

The effect of the low-temperature annealing of $n$- and $p$-type InSe single crystals on the photoelectric characteristics of $n$-InSe/$p$-InSe heterojunctions is investigated. It is found that the most pronounced enhancement of these characteristics takes place for annealing temperatures of 150–200$^\circ$C. Improvement in the quality of single-crystal samples upon annealing is confirmed by the observation of multiplet nuclear quadrupole resonance spectra, which reflect ordering in the system of polytypes of layered InSe crystals. For annealed materials, $n$-InSe/$p$-InSe structures exhibit an increase in the intensity of the exciton peak and an increase in the open-circuit voltage from 0.29 to 0.56 V and short-circuit current from 350 to 840 $\mu$A/cm$^2$.