We report electrical characteristics of 12 Ni Schottky contacts formed on an m-plane surface, which is a cleaved side surface of a c-plane free-standing n-GaN wafer. We observed a variety of distributions of surface steps with heights up to 5 nm in the contact area. The Schottky barrier heights obtained from current–voltage, capacitance–voltage, and photoresponce results distribute in a small range of 0.67–0.79 eV. The n-value is as good as 1.01 to 1.04. Independent of the step height, the barrier height and n-value variations are nearly absent. One possible reason for this is that the step facets consist of an m-plane. We found that the cleaving method can be utilized to form Schottky contacts on m-plane n-GaN surfaces in order to reveal the basic characteristics.
Electrical characteristics of a variety of Schottky contacts formed with ten metal species on the a-plane of p-type lowMg-doped GaN grown on r-plane sapphire substrates were studied. We found that while current-voltage characteristics obtained under voltage scanning show no memory effect in samples formed on a-plane samples on c-plane showed a substantial memory effects. We consider that the absence of memory effect in the a-plane p-GaN samples is originating from a smaller density of interfacial defect than that in the cplane p-GaN samples. In internal photoemission spectra, we observed two linearly increasing portions suggesting two different Schottky barriers with different heights coexisting in a contact. A potential barrier corresponding to a linear increase locating at lower photon energy typically ranged between 1.6 and 2.5 eV; and that corresponding to another linear increase locating at higher energy ranged between 0.7 and 1.7. The barrier heights showed no relevance to metal work function. The a-plane GaN surface was found to reveal a lamellar structure with stripes along [0001] direction with a randomly oriented roughness. We thus speculate that contact barrier spatially varies according to the different crystal plane.
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