THERMAL-CONDUCTIVITY REDUCTION IN GAAS-ALAS DISTRIBUTED BRAGG REFLECTORS

Self-heating of vertical-cavity laser diodes is strongly affected by t he thermal conductivity of the distributed Bragg reflectors (DBR's). B inary GaAs-AlAs DBR's are expected to be good heat conductors, but inv estigations of GaAs-AlAs superlattices indicate strong interface scatt ering of phonons. For the first time, we present direct thermal conduc tivity measurements of separated GaAs-AlAs DBR's with a quarter-wave l ayer thickness of more than 100 nm (tuned to 1.55-mu m wavelength). Us ing 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.