Multilayer thermionic cooling in GaAs-Al[x]Ga[1-x]As heterostructures

This thesis reports the experimental studies of cooling effect due to thermionic emission of electrons over periodic barriers in a semiconductor multilayer structures. The multilayer thermionic coolers investigated in this thesis, consisted of ten periods, each with 50 nm thick, undoped GaAs-Alo.07Gao.93As barrier layers, surrounded by heavily doped n-GaAs cathode and anode layers each with thickness of 100 nm. Current-voltage (I-V) characteristics of the devices were found to be nonlinear, but symmetrical when under forward and reverse bias. They behaved like Schottky diodes. In contrary, I-V characteristics of the substrates itself (as a reference device) were non-linear, but highly asymmetric. They acted like a p-n diodes. Temperature measurements of the devices and substrates have not yet shown any relative cooling exhibited by the multilayer thermionic coolers designed in this thesis. The difficulty in measuring cooling of the devices was due to the large Joule heating generated in the thick substrate.