INFLUENCE OF POTENTIAL FLUCTUATIONS ON ELECTRICAL-TRANSPORT AND OPTICAL-PROPERTIES IN MODULATION-DOPED GAN AL0.28GA0.72N HETEROSTRUCTURES/

We report transport and optical data for GaN/Al0.28Ga0.72N modulation- doped heterostructures grown by metal-organic chemical-vapor depositio n. Variable temperature galvanomagnetic, resistivity, photoluminescenc e, and photoconductivity measurements have been performed. Evidence fo r potential fluctuations is provided by the observation of weakly loca lized transport at low temperatures, together with a negative magnetor esistance due to disorder in the interface region. The deduced localiz ation criteria based on the theoretical modeling from Hall, resistivit y and negative ma,magnetoresistance data are in a reasonable agreement with weak-localization conditions. Additional evidence for a built-in electric field caused by the fluctuations near the heterointerface re gion is given by the observation of photoconductivity dips resonant wi th free excitons, indicating free-exciton ionization. A theoretical mo deling of the transport properties under various limiting scattering c onditions is provided, and compared with the experimental data for the transport time and elastic lifetime. The potential fluctuations in th e two-dimensional plane from the impurity distribution only are also m odeled, and the results are consistent with the experimental indicatio ns for strong potential fluctuations. It is concluded that interface r oughness, dislocations, and similar structural defects have a strong i nfluence on the transport properties of the two-dimensional electron g as in these structures. [S0163-1829(98)06224-9].