Investigation of Carrier Transport in Germanium MOSFETs With $\hbox {WN}/\hbox {Al}_{2}\hbox {O}_{3}/\hbox {AlN}$ Gate Stacks

To improve source injection velocity and consequently MOSFET performance, high mobility semiconductors are being explored as possible replacements for silicon. Germanium offers enhanced electron mobility and superior hole mobility at high inversion charge density; however, formation of a high quality germanium-dielectric interface remains a serious challenge. High-K dielectrics deposited directly on germanium exhibit poor physical and electrical properties, so an interfacial layer is required. Proposed interlayers include GeON, Si, and metal nitrides such as AlN and Hf₃N₄. To date, reported electron mobilities have been disappointing. In this letter, carrier transport in Ge MOSFETs with WN/AI₂O₃AIN gate stacks is investigated using surface-channel and buried-channel devices. Peak mobilities of 300 and 600 cm²/ V ldr s are observed for buried-channel p- and n-FETs, respectively. Evidence of phosphorus passivation of the germanium-dielectric interface is also presented.