Journal of Heat Transfer · 1994 · 188 citations · 0 references
EngineeringElectrical EngineeringMaterials ScienceOptoelectronicsSemiconductor DevicesThin FilmsSemiconductor LasersSemiconductor PhysicsSemiconductor Thin FilmsTemperature MeasurementThermal DiffusivityThermal Properties Of SemiconductorsAnisotropic Thermal DiffusivitySemiconductor Temperature SensorsTemperature-dependent Thermal DiffusivityThermal Diffusivity AnisotropyThermal Diffusivity In Thin FilmsThermal Diffusivity MeasurementThin Film Thermal TransportVertical-cavity Surface-emitting Lasers
The study introduces a new technique to measure thermal diffusivity of GaAs/AlGaAs thin films in both parallel and perpendicular directions and reports experimental results. The method employs a modulated laser to heat the film while a fast-response temperature sensor patterned on the sample records the thermal response, and the phase delay between heating and sensor signal yields diffusivity in the chosen direction, applied to an MBE-grown VCSEL with substrates etched away to eliminate substrate–film interface effects. The VCSEL structure’s thermal diffusivity is 5–7 times lower than bulk, and the experiments reveal anisotropy arising solely from thin-film interfaces and boundaries.
This work develops a new measurement technique that determines the thermal diffusivity of thin films in both parallel and perpendicular directions, and presents experimental results on the thermal diffusivity of GaAs/AlGaAs-based thin-film structures. In the experiment, a modulated laser source heats up the sample and a fast-response temperature sensor patterned directly on the sample picks up the thermal response. From the phase delay between the heating source and the temperature sensor, the thermal diffusivity in either the parallel or perpendicular direction is obtained depending on the experimental configuration. The experiment is performed on a molecular-beam-epitaxy grown vertical-cavity surface-emitting laser (VCSEL) structure. The substrates of the samples are etched away to eliminate the effects of the interface between the film and the substrate. The results show that the thermal diffusivity of the VCSEL structure is 5–7 times smaller than that of its corresponding bulk media. The experiments also provide evidence on the anisotropy of thermal diffusivity caused solely by the effects of interfaces and boundaries of thin films.