LOW-NOISE CHARACTERISTICS OF PULSE-DOPED GAAS-MESFETS WITH PLANAR SELF-ALIGNED GATES

We report on the low-noise characteristics of pulse-doped GaAs MESFET's. The pulse-doped structure consists of an undoped GaAs buffer layer, a highly doped thin GaAs active layer, and an undoped GaAs cap layer grown by organometallic vapor phase epitaxy. Even though the electron mobility of this structure is 1500 cm2/V . s, the noise figures obtained are 0.72 dB at 12 GHz and 1.15 dB at 18 GHz. In addition, the noise figures are insensitive to the drain current. It was found that the noise characteristics improve as the active layer of the pulse-doped MESFET becomes thinner. These mechanisms can explain the cancellation effect between the drain noise current and gate-induced noise current as reported for HEMT's.