Thermal conductivity reduction in GaAs-AlAs distributed Bragg reflectors

Self-heating of vertical-cavity laser diodes is strongly affected by the thermal conductivity of the distributed Bragg reflectors (DBRs). Binary GaAs-AlAs DBRs are expected to be good heat conductors, but investigations of GaAs-AlAs superlattices indicate strong interface scattering of phonons. For the first time, we present direct thermal conductivity measurements of separated GaAs-AlAs DBRs with a quarter-wave layer thickness of more than 100 nm (tuned to 1.55-μm wavelength). Using an ac calorimetric method and finite element analysis, we measure about 50% thermal conductivity reduction compared to the average bulk value. GaAs-AlAs DBR's for shorter wavelengths are expected to show an even lower thermal conductivity.