Low-frequency noise and phase noise in MESFETS with LTG-GaAs passivation

We report measurements of the low-frequency noise and phase noise of conventional unpassivated GaAs metal semiconductor field-effect transistors (MESFETs) and of MESFETs fabricated using an overlapping-gate structure and the low-temperature grown (LTG) GaAs as a passivation layer. The noise of the LTG-GaAs passivated MESFET was found to behave quite differently from that of a conventional MESFET and to be significantly reduced at low offset frequencies. These observations are explained in terms of the surface passivating effect of the LTG-GaAs. Low-frequency noise measurements seem to support the idea that the LTG-GaAs passivation reduces the number of active traps, in particular traps with large activation emergies. These results indicate that LTG-GaAs passivation can substantially reduce the near-carrier phase noise of MESFET-based oscillators.