Charge control model of the double delta-doped quantum-well field-effect transistor

The charge control properties of Al/sub 0.3/Ga/sub 0.7/As-GaAs-Al/sub 0.3/Ga/sub 0.7/As quantum-well field-effect transistor (FET) with double /spl delta/-doped planes are studied theoretically. A simple capacitor-like charge control model for the double/spl delta/-doped quantum-well FET's has been proposed and verified through self-consistent calculation. The threshold voltage and the capacitance can be related to the structure through simple analytical equations. The effective separation between capacitor plates is found to be the thickness of AlGaAs layer d+d/sub i/+/spl delta/ plus a correction term to account for the distribution of N/sub 2DEG/ inside the GaAs quantum well. For small well widths, only the ground-state subband is occupied and there is a simple linear relation between N/sub 2DEG/ and the gate bias V/sub G/. For larger well widths, electrons occupied the lowest subband, then the next higher energy subband, and the relation between the N/sub 2DEG/ and the V/sub G/ can be divided into piece-wise linear regions.<
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