DX centers in Al0.37Ga0.63As/GaAs and In0.34Al0.66As/In0.36Ga0.64As heterostructures

Electrical and galvanomagnetic measurements, made on modulation delta-doped -(Si) Al0.37Ga0.63As/GaAs and In0.34Al0.66As/In0.36Ca0.64As heterostructure s, fabricated into modulation doped field effect transistor-like gated Hall bars, were used to determine their DX center energies and densities in the normal and persistent photoconductive mode. Self-consistent Poisson/Schrod inger simulations of the gate voltage dependence and of the temperature dep endence of the charge transport parameters of these heterostructures provid e the position of the Fermi levels in the barrier layers, E-FB, relative to the conduction band minima and the electron densities in their quantum wel ls. The energy, E-DX=0.14 eV of Al0.37Ga0.63As determined from the temperat ure independent equilibrium position of E-FB is consistent with the average of the three lowest DX center energies of this alloy. It is also consisten t with that determined by others, on epitaxial Al0.37Ga0.63As layers, using conventional Hall measurement, deep level transient spectroscopic and hydr ostatic pressure measurements. Strain relaxed In0.34Al0.66As/In0.36Ga0.64As heterostructures, grown on GaAs substrates, were used for similar measurem ents and simulations. These yield the energy of the DX centers in In0.34Al0 .66As, relative to its Gamma-valley minimum, E-DX = 0.18 eV. This value in conjunction with the previously determined DX center energies of AlAs and t hat of In0.52Al0.48As, above its conduction band edge, E-DX(x) is correlate d with, but not identical to, the composition dependence of the L band of I nxAl1-xAs. (C) 1999 American Vacuum Society. [S0734-211X(99)07004-3].