Improved Schottky gate characteristics for MOVPE-grown GaAs MESFETs

Undoped surface layers of GaAs and Al0.50Ga0.50As, 50-300 Å thick, are shown to improve Schottky diode characteristics on heavily doped GaAs. As the thickness of the undoped GaAs spacer is increased from 0 to 300 Å, the reverse leakage current decreases by about 2 orders of magnitude and the effective barrier height increases from 0.45 to 0.67 eV. Al0.50Ga0.50As is much more effective in improving the diode characteristics for two reasons: (1) the larger bandgap results in an increased barrier height and (2) the larger effective mass further reduces the tunneling current. This is seen in a > 106 reduction in reverse current and barrier height increase from 0.47 to 1.0 eV as the Al0.50Ga0.50As thickness is increased from 0 to 300 Å. © 1992.