Theoretical and experimental capacitance-voltage behavior of Al0.3Ga0.7As/GaAs modulation-doped heterojunctions: Relation of conduction-band discontinuity to donor energy

Abstract

For the first time, we show that the capacitance-voltage behavior of modulation-doped heterojunctions may be accurately described by a first-principles theory that includes self-consistent quantum two-dimensional (2-D) electron subbands in the GaAs, numerical solution of Poisson’s equation for band bending and space charge in the (Al,Ga) As, and series resistance in the 2-D channel and heterointerface. The excellent agreement found between the theory and measurements on selected high-quality Al0.3Ga0.7As/GaAs heterojunctions allows accurate determination of the maximum 2-D carrier concentration. From this, we find a strong relationship between the conduction-band discontinuity and donor binding energy, giving offsets of 76 and 66% of the direct gap discontinuity for binding energies of 66 and 30 meV, as derived from published data.