Step-like heterostructure barrier varactor

Abstract

Conduction mechanisms in step-like heterostructure barrier varactor (HBV) have been investigated by means of measurements of current- and capacitance-voltage (C-V) characteristics. For this purpose, In/sub 0.53/Ga/sub 0.47/As/In/sub 0.52/Al/sub 0.48/As/AlAs single barrier varactors have been fabricated and characterized from room temperature up to /spl sim/400 K. The devices exhibit state-of-the art results with a breakdown voltage (V/sub b/) of /spl sim/6 V for a leakage current of 10 A/cm/sup 2/, a C-V ratio of 5:1 and a 0 V capacitance of 2 fF//spl mu/m/sup 2/. By solving the Poisson equation in the Thomas-Fermi approach and the Schrodinger equation, it is shown that the leakage current mechanisms are dominated by a resonant tunneling contribution below the voltage threshold. Subsequently, the results are interpreted in terms of an apparent barrier height equal to 600 meV near equilibrium. Above threshold, we attribute the drastic increase in the current-voltage relationship to impact ionization.