Pb$_{1-x}$Eu$_{x}$Te (0 $\le x \le$ 1) as materials for vertical-cavity surface-emitting lasers in the mid-infrared spectral range of 4–5 $\mu$m

The optical properties of epitaxial layers and heterostructures based on Pb$_{1-x}$Eu$_{x}$Te alloys (0 $\le x \le$ 1) are analyzed in the context of designing Bragg mirrors and vertical-cavity surface-emitting lasers for the midinfrared spectral range. It is shown that the optimal heteropair for laser microcavities is Pb$_{1-x}$Eu$_{x}$Te ($x\approx$ 0.06)/EuTe. On the basis of this heteropair, highly reflective Bragg mirrors consisting of just three periods and featuring a reflectance of $R\ge$ 99.8% at the center of the stop band are grown by molecular-beam epitaxy on BaF$_2$ (111) substrates. Single-mode optically pumped vertical-cavity surface-emitting lasers for the 4–5 $\mu$m spectral range operating at liquid-nitrogen temperatures are demonstrated.