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 Al_0.3Ga_0.7As/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.