Characterization of Single Barrier Microrefrigerators at Cryogenic Temperatures

Abstract

The experimental characterization of single barrier heterostructure thermionic cooling devices at cryogenic temperatures is reported. The device studied was a cylindrical InGaAs microrefrigerator, in which the active layer was a 1 lm thick In 0.527 Al 0.218 Ga 0.255 As heterostructure barrier with n-type doping concentration of 6.68 9 10 16 cm À3 and an In 0.53 Ga 0.47 As emitter/collector of 5 9 10 18 cm À3 n-doping. A full field thermoreflectance imaging technique was used to measure the distribution of temperature change on the deviceÕs top surface when different current excitation values were applied. By reversing the current direction, we studied the deviceÕs behavior in both cooling and heating regimes. At an ambient temperature of 100 K, a maximum cooling of 0.6 K was measured. This value was approximately one-third of the measured maximum cooling value at room temperature (1.8 K). The paper describes the deviceÕs structure and the first reported thermal imaging at cryogenic temperatures using the thermoreflectance technique.

Nanoscale solid-state cooling: a review

“…This method is sensitive to mK temperature fluctuations with a sub-nanosecond temporal resolution and can produce images with submicron spatial resolution [207]. TR Thermal imaging has been extensively used to characterize thermoelectric devices, and in particular integrated microcoolers [65,75,205,208]. For steady-state characterizations, a sinusoidal bias signal is supplied to the device under test (DUT) for a period several orders of magnitude longer than the relevant thermal time constants of the sample.…”