Influence of top surface passivation on bottom-channel hole mobility of ultrathin SiGe- and Ge-on-insulator

Abstract

Bottom-channel hole mobility was examined by a pseudo-metal-oxide-semiconductor field-effect transistors method for ultrathin SiGe-on-insulator (SGOI) and Ge-on-insulator (GOI), which were fabricated using Ge condensation by dry oxidation. By comparing samples with and without a top SiO2 layer, we investigated the influence of top surface passivation on bottom-channel hole mobility. Mobility degradation was found in an ultrathin SGOI/GOI layer without top SiO2 and became more serious with a decrease in the thickness of the SGOI/GOI layer, which strongly suggested that top surface passivation is necessary to evaluate accurate channel mobility. A 13-nm-thick GOI with passivation showed a high mobility value of 440 cm2/V s.

Effective passivation of defects in Ge-rich SiGe-on-insulator substrates by Al2O3 deposition and subsequent post-annealing

“…However, with an increase in Ge%, I off drastically increases for as-fabricated SGOI's. This phenomena have been observed by other group and our previous work [5,10]. When Ge% increases to 90%, the I on/off ratio decreases to less than 10 4 .…”

“…As a result, holemobility enhancement factor of approximately 10 has been successfully demonstrated in the condensed SGOI [4]. However, it is noticeable that structural defects such as stacking faults and microtwins were unintentionally induced in Ge-rich SGOI due to strain relaxation during high-temperature oxidation [5][6][7], and defect-free SGOI with Ge% higher than 82% can not be obtained regardless of the initial parameters [7]. Furthermore, these electrically active defects act as acceptors, which cause a hole concentration (N p ) and acceptor concentration (N A ) as high as 10 16 -10 18 cm À3 in Ge-rich SGOI [8,9].…”

“…Fig. 7 shows the bottom-channel hole mobility for SGOI's with and without Al 2 O 3 -PDA, which were obtained by using the I D -V G characteristics of pMOSFET [5]. Although Al 2 O 3 -PDA can effectively improve the I on/off ratio by decreasing I off , Fig.…”

“…Furthermore, these electrically active defects act as acceptors, which cause a hole concentration (N p ) and acceptor concentration (N A ) as high as 10 16 -10 18 cm À3 in Ge-rich SGOI [8,9]. As a result, a p-channel metal-oxide-semiconductor field-effect transistor (MOSFET) on Ge-rich SGOI exhibits a large off current (I off ) and is difficult to operate in full depletion (FD) mode [5,10]. nMOSFET on Ge-rich SGOI exhibits a high threshold voltage (V T ) [8].…”

Probing the electronic structure at semiconductor surfaces using charge transport in nanomembranes

“…In the current measurements, the free surface is atomically clean, but that is not a requirement for general application of the method. Any changes 4,[11][12][13] in the front surface act as an additional gate to counter or enhance the effect of the back gate. The NM bulk conductance is continuously tunable by the back-gate voltage and hence can be made negligible relative to the surface contribution.…”