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Title: Low thermal conductance platforms for mK tunnelling coolers
Author: Wongwanitwattana, Chalermwat
ISNI:       0000 0004 5348 3237
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2015
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The impact of the O2 content in SF6-O2 gas mixtures on the etch rate and sidewall profile of Silicon (Si), Germanium (Ge) and phosphorous doped Germanium (Ge:P) in reactive ion etching has been studied. The characteristics of etch rate and sidewall profile were greatly affected by the O2 content. Below 50% of O2 content, a large variation in Ge etch rates was found compared to that of Si, but for O2 content above 50% the etch rates followed relatively the same trend. Lightly doped Ge showed the highest etch rate at a O2 concentration up to 20%. Sidewall angles range from a minimum of 80° to a maximum of 166°, with O2 concentration of 20% yielding perfect anisotropic mesa etch. Also at this O2 concentration, reasonable Si/Ge selectivity was possible. These observations indicate that by adjusting the O2 concentration, precision plasma etching of Si, Ge and Ge:P was possible. Suspended Ge structures were fabricated: micro wires, spiderweb and the van der Pauw Greek-cross. The micro wires’size could be reduced to fabricate suspended Ge nanowires devices. The suspended spiderweb could be fabricated for bolometers. The van der Pauw Greek-cross structure could reveal the electrical properties of thin expitaxial layer such as resistivity and mobility via hall measurement as a function of temperature. Removal of dislocations was shown to enhance the electrical isolation. Thermal properties of germanium doped with phosphorus (4x1019 cm-3) were investigated in this study. At lowest Tbath of 312 mK , the results indicate that heat flow from hot electrons to phonons was proportional to T7 and the electron-phonon coupling constant is 1.31x109 W/m3 K7 . The temperature dependence of doped Ge was higher than doped Si (which has a T6 temperature dependence) because the band structure was different. Moreover, the heat flow between electrons and phonon that is proportional to T7 could possibly be explained by a combination of strong disorder and surface modes.
Supervisor: Not available Sponsor: Government of Thailand
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics