Optically pumped Pb$_{1-x}$Sn$_x$Se$_{1-y}$Te$_y$ heterojunction lasers with matched gratings at the interface

An investigation was made of the photoluminescence emitted from epitaxial films of Pb$_{1-x}$Sn$_x$Se$_{1-y}$Te$_y$ solid solutions ($0\le x\lesssim0.47$; $0\le y\lesssim0.65$), grown by the method of liquid epitaxy on $n$-type PbSe substrates. Next, $n$-Pb$_{1-x}$Sn$_x$Se$_{1-y}$Te$_y/n$-PbSe heterostructures, with the Pb$_{1-x}$Sn$_x$Se$_{1-y}$Te$_y$ active layer ($0.015\le x\le0.092$; $0.006\le y\le0.026$), were matched in respect of the lattice constant to the substrate ($\Delta a/a\approx10^{-1}-10^{-3}$ %) and used as optically excited heterolasers. The spectral and threshold characteristics were determined as a function of the thickness of the active layer $d$ , temperature, and resonator length. Variation of the composition of the active layer altered the emission wavelength within the range $8-12.5\mu$ at 77$^\circ$ K. Electron and optical confinement effects were observed when the thickness $d$ was reduced. For the optimal thickness $d_{\text{opt}}\approx2.5\mu$ at 77$^\circ$ K. The loss factor (5.5 cm$^{-1}$), gain (0.11 cm/W), and carrier density ($2\times10^{-17}$ cm$^{-3}$) in the active layer were determined.