Defect level induced peak in the capacitance-voltage plots of Al/n-GaAs/In and W/n-GaAs/In devices fabricated by RF sputtering

The 1 MHz capacitance-voltage (C-V) measurements were performed on five Schottky diodes (four W/n-GaAs/In diodes and one Al/n-GaAs/In diode) fabricated by rf sputtering, and one Al/n-GaAs/In diode fabricated by thermal deposition. A peak in the 1 MHz capacitance-voltage (C-V) plots and a minima in the 1 MHz C^-2-V plots of all diodes fabricated by sputtering were observed. Such a peak or minima was absent in the diode fabricated by thermal evaporation. Using the Chan and Shih model, the series resistance of the devices was estimated from the value C^-2 at minima of the C^-2-V plots which was 18-20 times greater than the actual value of 3.6 Ω determined from the I-V characteristics of the In/n-GaAs/In ohmic structure fabricated on the same substrate used in the device fabrication. This fact provided a clear evidence that the minima in the C^-2-V plots of diodes fabricated by sputtering was not due to series resistance, but was related to the process of fabrication of the metal rectifying contact by rf sputtering. The observed peak in the C-V plot may be caused by the presence of high concentration acceptor type traps induced by rf sputtering near the metal/n-GaAs interface, during sputter etching of the polished surface of n-GaAs or sputter deposition of the metal. By comparing the linear portions of the C^-2-V plots of diodes fabricated by sputtering with the Mott-Schottky plot of the diode fabricated by thermal method, some estimates of the concentration of the sputter induced donor defects is also made