FIG.35 Transconductance gm ≡ ∂I/∂VSD of the device of FIG.34 measured as a function of gate voltage for various values of the source-drain voltage. The oscillations, seen in particular at low source-drain voltages, are attributed to Bragg reflection in a periodic potential. Taken from K. Ismail et al., Appl. Phys. Lett. 52, 1071 (1988).