Large negative magnetoresistance induced by interplay between smooth disorder and antidots in AlGaN/GaN HEMT structures

Large low temperature negative magnetoresistance (NMR) experimentally observed in AlGaN/GaN high electron mobility transistors (HEMT) structures grown by metalorganic chemical vapour deposition on sapphire substrate has been reported. A linear B⁻¹ ln B dependence of magnetoresistance observed in our samples indicates the presence of random antidot array together with smooth disorder. It is proposed that the antidots are linked with high bandgap AlN rich regions formed due to possible Al–Ga segregation at the interface during growth and the smooth random disorder is due to interface roughness. The antidot density is estimated to be of ∼7 to 8 × 10¹⁰ cm⁻² in our samples. The magnitude of NMR is also correlated with the extent of interface roughness indicated by x-ray reflectivity. It is also proposed that the formation of antidots is related with the lattice mismatch between substrate and epitaxial heterostructures. The NMR in AlGaN/GaN HEMT structures grown on SiC substrates having relatively lower lattice mismatch has been shown to have a usual B ² and ln T dependences indicating only electron–electron interaction and absence of antidot-like scatterers. (paper)