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 Poisson equation. The capacitance was calculated by considering the displacement current and electron density distribution in the device in detail. GaAs/Al0.3Ga0.7As diodes with different undoped spacer layers but identical quantum well structure have been studied and compared. The capacitance was found to decrease generally with increasing spacer layer. The experimental peak in the capacitance-voltage (C-V) measurements has been observed in the calculations. The result shows that a longer cathode spacer layer can result in a higher peak in the C-V characteristic, while the anode spacer layer has relatively small effect on the peak. The optimum choice for spacer layers for higher cutoff frequency are discussed.