Thermal conductivity of Ga1−xAlxAs alloys

This paper presents the results of our measurement of the room-temperature thermal conductivity of the Ga1−xAlxAs alloy system. The study was motivated by our need to characterize the thermal properties of cw heterostructure lasers, in which the heat generated in the optically active layer must flow through a substantial thickness of Ga1−xAlxAs to reach the heat sink. The measurement was made on LPE layers which were separated from their substrates and fashioned into rectangular bars. A steady-state heat flow was established in the bars utilizing an argon laser as the heat source, and the conductivity was obtained by measuring the temperature gradient in the bars with thin films of cholesteric liquid crystals. The results indicate that the thermal conductivity of the alloy is well described by an existing theoretical treatment of high-temperature lattice thermal conductivity of disordered semiconductor alloys. In the Ga1−xAlxAs system, the increased thermal resistivity of the alloy is shown to be a result of phonon scattering from mass defects and not lattice strain, which is negligible due to the excellent lattice parameter match of GaAs and AlAs.