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With continued scaling down of devices it is necessary to look into new materials in order to improve device performance. Ge and SiGe are good candidates for channel materials since they present high carrier mobility. Also, in order to reduce the gate leakage as the dielectric thickness is reduced it is necessary to look at high-κ materials to substitute the Si-SiO2 as it reaches its limits. This thesis investigates different properties of Ge devices. The first part of this work investigates Ge channel MOSFETs and the effects of different growth parameters such as Ge surface passivation scheme, channel thickness and doping concentration on device performance. It is shown that, for these devices, strain can provide a 50% increase in mobility, but channel thickness and doping concentration do not show significant enhancement in mobility. The second part looks at the transport properties of very high mobility, strained Ge channel, modulation doped devices. A mobility of around 7 x 105 cm2V-1s-1 was measured at 300 mK for a Ge heterostructure grown by CVD. Values for the hole effective mass of 0.083±0.002 m0 were obtained from the temperature and field dependence of Shubnikov-de Hass oscillations in the magnetoresistance. In the last chapter, developments on thermal growth of GeO2 are investigated using a simple oxidation process. It is shown that this process demonstrates good device characteristics and a smooth Ge-GeO2 interface. For devices under study an interface trap density around 1011 eV-1cm-2 is estimated using the low-high frequency method. |
