1/f noise in MODFETs at low drain bias

The 1/f noise in normally-on MODFETs biased at low drain voltages is investigated. The experimentally observed relative noise in the drain current S/sub I//I/sup 2/ versus the effective gate voltage V/sub G/=V/sub GS/-V/sub off/ shows three regions which are explained. The observed dependencies are S/sub I//I/sup 2/ varies as V/sub G//sup m/ with the exponents m=-1, -3, 0 with increasing values of V/sub G/. The model explains m=-1 as the region where the resistance and the 1/f noise stem from the 2-D electron gas under the gate electrode; the region with m=0 at large V/sub G/ or V/sub GS/ equivalent to 0 is due to the dominant contribution of the series resistance. In the region at intermediate V/sub G/, m=-3, the 1/f noise stems from the channel under the gate electrode, and the drain-source resistance is already dominated by the series resistance.<
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