Physics, growth, and performance of (In,Ga)As-AlP/InP quantum-cascade lasers emitting at lambda < 4 mum

The design strategy and performance for short wavelength ( 4 m) quantum-cascade lasers (QCLs) is discussed. The QCLs are based on strain-compensated AlAs-In0.73Ga0.27As heterostructures grown using gas-source molecular-beam epitaxy on InP substrates. Both composite barriers based on AlAs-In0.55Al0.45As and composite wells based on In0.73Ga0.27As-In0.55Al0.45As are used to achieve laser emission at wavelengths as short as 3.05 mum by avoiding leakage from the upper laser state into either the higher-lying miniband or into indirect states within the heterostructure.