EFFECT OF SPACER LAYERS ON CAPACITANCE OF RESONANT-TUNNELING DIODES

The capacitances of double barrier resonant tunneling diodes have been obtained by calculating the charge distributions in the devices self- consistently. Self-consistent calculations were performed based on the solutions of the time-independent Schrodinger equation and the Poisso n equation. The capacitance was calculated by considering the displace ment current and electron density distribution in the device in detail . GaAs/Al0.3Ga0.7As diodes with different undoped spacer layers but id entical quantum well structure have been studied and compared. The cap acitance was found to decrease generally with increasing spacer layer. The experimental peak in the capacitance-voltage (C-V) measurements h as been observed in the calculations. The result shows that a longer c athode spacer layer can result in a higher peak in the C-V characteris tic, while the anode spacer layer has relatively small effect on the p eak. The optimum choice for spacer layers for higher cutoff frequency are discussed.