| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
I8,Temperature-Dependent Thermal Properties of HgCdTe Superlattices |
| Author(s) |
Kejia Zhang, Abhishek Yadav, Lei Shao, Ramana Bommena, Jun Zhao, Silviu Velicu, Kevin P. Pipe |
| On-Site Speaker (Planned) |
Kejia Zhang |
| Abstract Scope |
HgCdTe has demonstrated high performance for mid- to long-wavelength infrared detection applications; in particular, HgCdTe-based superlattices have shown promise as a means to tune the cutoff wavelength by adjusting the constituent layer thicknesses. Furthermore, because of its high electrical mobility and low thermal conductivity, HgCdTe has potential as a high-efficiency thermoelectric material. Optimizing the thermoelectric properties of HgCdTe superlattices could lead not only to thermoelectric modules with high thermoelectric figure-of-merit but also to microscale thermoelectric coolers that are monolithically integrated with infrared detector pixels for localized cooling. Because of the reductions in thermal conductivity known to occur in superlattices due to increased phonon scattering, measurements of the thermal properties of HgCdTe SLs are important both for the thermal management of infrared detectors as well as the improvement of the material’s thermoelectric figure-of-merit. As with other materials for infrared detection, HgCdTe is most commonly used at low temperatures to increase signal-to-noise. In this work we present measurements of the thermal properties of MBE-grown Hg0.8Cd0.2Te/Hg0.2Cd0.8Te (200Å/400Å) superlattices over a range of temperature (80K – 295K). In particular, we show measurements of the cross-plane thermal conductivity obtained using a differential 3ω method on samples with SL thicknesses of 600nm to 2.4μm. These measurements confirm a superlattice thermal conductivity that is significantly lower than the bulk values of either binary (HgTe or CdTe) or the ternary (Hg1-xCdxTe). A 3ω heater wire was first lithographically defined on each sample; samples were then mounted on the cold finger of a cryostat using a removable copper block. The contact pads of the heater wire were wirebonded to external beryllium oxide chips with separate heatsinks; the beryllium oxide chips were in turn connected to a 10-pin vacuum feedthrough using copper wires. A copper cylinder was used as a radiation shield to remove parasitic temperature gradients caused by radiative heat transfer between the cold finger and surroundings. The electronic measurement setup included a harmonic oscillator used to drive a bidirectional current source; the bidirectional current source consisted of a Howland current pump circuit and buffer amplifier to increase the current output. The current through the heating wire was determined by connecting a precision heat sink resistor in series with the wire and measuring the 1ω voltage drop across it using a lock-in amplifier. The temperature coefficient of resistance was determined by slowly heating the wire from 80K to 295K and measuring the resistance of the wire using a four-probe method while simultaneously measuring the sample temperature. The 3ω voltage (from which thermal conductivity was derived) was measured using a lock-in amplifier. |
| Proceedings Inclusion? |
Undecided |