Characterization of MESFET and MODFET microwave noise properties utilizing drain noise current

The microwave drain noise characteristics have been studied for conventional long gate (1.0- mu m and 0.5- mu m) GaAs MESFETs and short ( approximately=0.15- mu m) strained InGaAs/InAlAs/InP MODFETs (modulation-doped field-effect transistors). Although the MODFETs have lower noise figures (F/sub min/ approximately=0.4 dB at 10 GHz) than the MESFETs (1.5 dB at 10 GHz), their measured drain noise currents are greater, indicating that F/sub min/ does not describe the true device noise characteristics. Due to higher gain, estimated parasitic contribution to the device noise is greater for the MODFETs than the MESFETs. The intrinsic channel noise has been modeled with an effective temperature associated with r/sub ds/, showing that carrier heating alone cannot explain the measured characteristics.<>