Current transport mechanisms in Pt/Au Schottky contacts to AlInGaN using AlGaN/InGaN short-period superlattices

High-quality AlInGaN film grown by metal organic chemical vapor deposition is realized by fabricating the AlGaN/InGaN short-period superlattices, and then, Schottky contacts are fabricated on the AlInGaN superlattices. The crystal quality of AlInGaN superlattice samples is characterized by X-ray diffraction and scanning electron microscopy, and the correlation between the compositions of AlInGaN and growth condition is further clarified. The current transport mechanisms of the Pt/Au Schottky contacts to AlInGaN superlattice samples with different background carrier concentrations are studied by current–voltage (I–V) characteristics and theory analysis based on the thermionic emission (TE) and thermionic field emission (TFE) models. It is found that the results obtained from the TE and TFE models are almost identical for the Schottky contact to strain-balanced AlInGaN sample with low background carrier concentration, indicating that the thermionic emission is a dominant current transport mechanism. However, the Schottky contacts fabricated using high background carrier concentration AlInGaN samples demonstrate degraded barrier characteristics due to an occurrence of donor-like defects which result in the defect-assisted tunneling current, and thus, the combination of tunneling transport and thermionic emission constitutes the current transport mechanisms in Schottky contacts.