Material and Structure Factors Affecting the Large-Signal Operation of GaAs Mesfets
For typical recessed-gate FET structures, the drain characteristics at high drain voltages exhibit, to one degree or another, an increase in drain current for gate voltages where the channel would ordinarily be pinched off. In some devices, this ‘soft’ current is observed to depend on the speed of the bias sweep or pulse (80μs, 50 Hz) used to measure it. One possible consequence of soft breakdown is that it may restrict the available voltage swing across the device, and hence the r.f. power available in microwave circuit applications. It is shown that some features of the breakdown characteristic are consistent with the existence of deep levels in the n-channel and buffer epitaxial layers. Capacitance transient measurements upon finished FET structures reveal the presence of deep levels at concentrations above 1015 cm-3.
KeywordsBuffer Layer Deep Level Gate Voltage Drain Characteristic Slow Sweep
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