The Role of Acceptor Density on the High Channel Carrier Density I-V characteristics of AlGaAs/GaAs MODFETs
AEROSPACE CORP EL SEGUNDO CA LAB OPERATIONS
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A triangular-well, one-subband depletion layer model has been developed for the high density region of a modulation doped field-effect transistor MODFET. High density operation is defined as operation when the channel carrier density, in the entire channel, is equal to or greater than m1ktpi h-sq. This high density model has been used to describe the effects of the depletion layer charge on the I-V characteristics. An approximation for the experimentally determined threshold voltage is derived. For small acceptor densities, 10 to the 13th powercc, it is shown that the experimentally determined threshold voltage may differ from the strong inversion threshold voltage by 0.25 V. We show that this discrepancy is due to the effect of the depletion layer charge in the high density region. Also, the depletion layer charge is shown to account for the discrepancy in the device capacitance and the A1GaAs layer capacitance. The effective layer thickness delta is shown to decrease from 90 A at an acceptor density of 10 to the 13th powercc to 75 A at 10 to the 17th powercc.
- Electrical and Electronic Equipment
- Solid State Physics