Figure 1
From: Anomalous enhancement of the sheet carrier density beyond the classic limit on a SrTiO3 surface
Schematic pictures of the cross section and the band diagram of FET.
Neither distance nor energy of the picture scales to that of the real device. (a) The channel is an n-type non-metallic material (e.g., non-doped SrTiO3). By differentiating VG = Vins + φ with respect to n2D and by using the Gauss’s law, we obtain 
. (b) For larger VG, the channel becomes metallic and VG = Vins + μ/e. Same as (a) the relationship 
is obtained, where 
is called a quantum capacitance (ref. 2). 
becomes larger than 
only when 
is negative.
