Theory and design of In_xGa_1-xAs_1-yBi_y mid-infrared semiconductor lasers: Type-I quantum wells for emission beyond 3 μm on InP substrates

We present a theoretical analysis and optimisation of the properties and performance of mid-infrared semiconductor lasers based on the dilute bismide alloy In_xGa_1-xAs_1-yBi_y, grown on conventional (001) InP substrates. The ability to independently vary the epitaxial strain and emission wavelength in this quaternary alloy provides significant scope for band structure engineering. Our calculations demonstrate that structures based on compressively strained In_xGa_1-xAs_1-yBi_y quantum wells (QWs) can readily achieve emission wavelengths in the 3-5 μm range, and that these QWs have large type-I band offsets. As such, these structures have the potential to overcome a number of limitations commonly associated with this application-rich but technologically challenging wavelength range. By considering laser structures having (i) fixed QW thickness and variable strain, and (ii) fixed strain and variable QW thickness, we quantify key trends in the properties and performance as functions of the alloy composition, structural properties, and emission wavelength, and on this basis identify routes towards the realisation of optimised devices for practical applications. Our analysis suggests that simple laser structures - incorporating compressively strained In_xGa_1-xAs_1-yBi_y QWs and unstrained ternary In_0.53Ga_0.47As barriers - which are compatible with established epitaxial growth, provide a promising route to realising InP-based mid-infrared diode lasers.