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In this paper, we described the fabrication of GaN based diodes from two different structures , a bulk GaN p-n junction structure and a p-n junction structure incorporating a p-type AlGaN/GaN superlattice. This superlattice structure is included to facilitate ohmic contact formation. We measure the I-V characteristics of the p-n junctions at room temperature. The lower ideality factor to the improved transport characteristics of p-type AlGaN/GaN superlattices are attributed. The temperature dependence of ideality factor is obtained by measuring the I-V characteristics of the GaN p-n juction with the superlattice structure at three different temperatures. In addition, contact become less rectifying at higher temperatures and hence result in more ohmic behavior. This decreases the ideality factor of the metal-semiconductor juction, which in turn reduces the overall ideality factor. This interpretation is in excellent agreement with the theoretical model and the experimental results.