Electrical behaviour of lateral Al/n-GaN/Al structures

The electrical behaviour of lateral Al/n-GaN/Al structures has been studied by current–voltage measurements between a large pad with an area of 22 mm2 and small contacts with different areas in the range of 0.01–1 mm2. The results indicated that near room temperature the current was limited by the GaN layer exhibiting linear I–V characteristics for large contacts around 1 mm2, while it was contact limited for small contacts around 0.1 mm2 and below. This indicates that the same metal contact can behave as ohmic or rectifying depending on the contact area and so on the ratio of contact resistance to the series resistance of the structure. Near liquid nitrogen temperature, the current through the lateral Al/n-GaN/Al structures was limited by space charges. The Al/n-GaN contacts exhibited a very low Schottky barrier height below or around 0.2 eV. A new possible mechanism responsible for the temperature dependence of the ideality factor is proposed.