  Relations for the optimum well width, barrier width and width of the spacer
layer to achieve highest PVCR on the basis of effective mass and barrier height
in RTDs is proposed. The optimum spacer layer is found to be half of the
de-Broglie wavelength associated with the bound state of the corresponding
finite quantum well. The proposed relations for the optimum parameters can be
used to design RTD based on any two appropriate materials to attain highest
PVCR. The effect of doping concentrations on PVCR and peak current was studied.
As case study, we have considered the GaAs/Ga0.7Al0.3As and GaN/Ga0.7Al0.3N
RTDs. The current density obtained using the tunneling coefficient based on
transfer matrix approach takes in to account the variation in the electric
field in the well and barrier region on account of variation in the dielectric
constant in the material.
