Mass enhancement of two-dimensional electrons in thin-oxide Si-MOSFET's

We wish to report in this paper a study of the effective mass (m*) in thin- oxide Si-metal-oxide-semiconductor held-effect transistors, using the tempe rature dependence of the Shubnikov-de Haas (SdH) effect and following the m ethodology developed by J.L. Smith and P.J. Stiles, Phys. Rev. Lett. 29 102 (1972). We find that in the thin oxide limit, when the oxide thickness d(o x) is smaller than the average two-dimensional electron-electron separation r, m* is still enhanced and the enhancement can be described by m*/m(B) =0 .815+0.23(r/d(ox)), where m(B)=0.195m(e) is the bulk electron mass, m(e) th e free electron mass. At n(s)=6 x 10(11)cm(2), for example, m* similar or e qual to 0.25m(e), an enhancement doubles that previously reported by Smith and Stiles. Our result shows that the interaction between electrons in the semiconductor and the neutralizing positive charges on the metallic gate el ectrode is important for mass enhancement. We also studied the magnetic-hel d orientation dependence of the SdH effect and deduced a value of 3.0+/-0.5 for the effective g factor in our thin oxide samples. [S0163-1829(99)15615 -7].