AN ANALYSIS OF THE EFFECTIVE POSITION OF THE 2-DIMENSIONAL ELECTRON-GAS IN THE CHANNEL OF MODFET EPITAXIAL LAYER STRUCTURES

The charge control behavior of a range of heterostructure material sys tems typical of MODFET's has been investigated using a numerical model , and the ''effective position of the two-dimensional electron gas (2- DEG) in the channel,'' Delta d, has been analyzed. We have shown that the parameter Delta d is well-defined for double-heterojunction struct ures, though with values very different from the often-quoted figure o f 80 Angstrom [1], and that for AlGaAs/GaAs single heterojunctions, De lta d is strongly gate voltage dependent with values always larger tha n 80 Angstrom.