Optically pumped low-threshold UV lasers

Recently, low-threshold optically-pumped DUV lasers containing AlGaN-based multiple-quantum wells (MQWs) have been demonstrated by homoepitaxial growth on c-plane bulk AlN substrates [1–5]. The bulk AlN substrates were used in these studies due to low-dislocation density and reduction of the lattice mismatch and thermal expansion difference between the AlN substrate and Al-rich AlGaN epitaxial layers, thus leading to high-quality active regions with relatively low-dislocation density. However, because of high cost, smaller area, and impurity absorption of the bulk AlN substrates today, it is much more desirable to grow DUV lasers on the vastly available and lower-cost sapphire substrates.