Graded compositional heterostructures in the GaAs/Al xGa 1−xAs system

Abstract

A device exhibiting the characteristics of two anti-parallel Schottky diodes would allow the fabrication of a planar balanced mixer for millimetre wave communications. A suitable GaAs/Al xGa 1−xAs isotype heterostructure containing a highly symmetric triangular barrier of controlled height and width in the conduction band is described. Symmetric compositionally graded triangular barriers and quantum wells have been grown with barrier widths between 160 to 4000 Å using conventional solid source molecular beam epitaxy (MBE), by the continuous liner ramping of aluminium mole fraction from x=0 to the order of x=0.3. Current versus voltage ( I− V) characteristics have been measured over a range of temperatures and correlated with theoretical predictions. Triangular quantum well structures were also grown in the range of widths from 50 to 500 Å and have been studied by photoreflectance (PR) and differential photoreflectance (DR) techniques. Both types of device exhibit excellent symmetry and short, steep compositional profiles have been confirmed by direct secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) analysis on representative samples.