Study On The Performance Of Micro Thermoelectric Devices Based On InGaAs Quantum Dot Superlattice

Thermoelectric devices enable bidirectional conversion between thermal and electrical energy and hold great promise for overcoming the increasingly tough challenge of energy sustainability.The research of thermoelectricity is mainly divided into two aspects:device-level and material-level.The properties of thermoelectric materials fundamentally determine the thermoelectric conversion efficiency of thermoelectric devices.With more interfaces and defects than bulk materials as well as many unique physical effects caused by microstructure,low-dimensional nanothermoelectric materials exhbit great prospects in thermoelectric application.Quantum confinement effect changes the electron transport mechanism and makes it possible to break the upper limit of power factor.In this paper,we firstly introduced 2 nm self-assembly ErAs nanoparticles into the In0.53Ga0.47As superlattice using molecular beam epitaxy technique and experimentally verified that the nanoparticles below 3 nm triggered the zerodimensional quantum dot confinement.Each thermoelectric parameter of δ-BeErAs:In0.53Ga0.47As was characterized.The quantum confinement effect of the quantum dot superlattice structure was found to increase its power factor up to 445×10-6 W/mK2 at 516 K and by 4-5 times compared with the reference sample.Secondly,quantum dot superlattice thin films were fabricated using MEMS technique into micro thermoelectric devices containing 1-25 superlattice mesas with an maximum overall size up to 5.7×1mm2.When used to generate power,the 25 mesa device realized the output voltage of 0.105 V and maximum power output of 0.13 μW for ΔT of 19.6 K at Tavg of 516 K.The output parameter and maximum power can be further increased by increasing the number of semiconductor mesas N or changing the geometry of the mesas.Finally,a real time measurement method for thermal deformation of microscopic interfaces of thermoelectric device was proposed.The performance and reliability of commercial thermoelectric devices are generally influenced and constrained by thermal stresses and fatigue fracture at heterogeneous interfaces is a common problem in the working operation of devices.In this paper,a digital-image-correlation-based microscopic thermal deformation measurement method was introduced.A laserspeckle-based vacuum measurement system was set up with a speckle accuracy of 0.002 pixel.The method achieved a measurement error of less than 0.006 pixel and was validated in the measurement of full-field thermal deformation of TEC thermoelectric pillars in commercial thermoelectric coolers.Strain and stress distribution and its variation with the TEC operating temperature difference were studied with the stress concentration region identified.It was found that the maximum shear stress approached the fracture limit of the commercial thermoelectric material Bi2Te3 at a TEC operating temperature difference of about 60 K,which was consistent with the operation limit of commercial TEC and verified the reliability of this thermal deformation measurement method.The microscopic interface thermal deformation measurement method for thermoelectric device in this study is applicable to the direct observation of the thermomechanical behavior of Bi2Te3 thermoelectric pillars and also has great potential for the reliability prediction of micro thermoelectric devices,which provides a useful guideline for the design,manufacturing and optimization of thermoelectric devices.