En route to electrically pumped broadly tunable middle infrared lasers based on transition metal doped II-VI semiconductors

In this work we report the study of Cr2+:ZnSe photo-luminescence under UV and visible excitation as well as middle-infrared electroluminescence of n-type, Cr doped bulk ZnSe crystals. Photo-conductance studies were performed to verify (2+)→(1+)→(2+)* ionization transitions responsible for Cr2+ excitation. We report the first to our knowledge, Cr2+:ZnSe lasing using 532 nm excitation. The first ever room temperature electroluminescence was also achieved in bulk n-type Cr:Al:ZnSe. This electroluminescence over 1800-2800 nm spectral range is in a good agreement with the mid-IR Cr2+ fluorescence under intra-shell optical excitation. Other spectral bands of electroluminescence were also observed at 600 nm and 8 μm. The visible electroluminescence observed is attributed to Vzn-Al complexes in conductive crystals. The nature of the 8 μm electroluminescence requires additional studies. Photo-ionization results are essential for optical pumping of Cr:ZnSe by easily available visible lasers, and, most importantly, both these and the electroluminescence results open a pathway for Cr:ZnSe broadband mid-IR lasing under direct injection of free carriers. Future directions for electrical excitation of low dimensional II-VI structures, where quantum confinement of the atomic impurity is used, could result in a much more efficient transfer of energy from the host to the localized impurity, are discussed.