The leakage mechanism of large size GaN p–i–n diodes is studied, and the possible reasons are analyzed. It is found that (i) the leakage current of most diode chips is not proportional to their area, and the leakage problem deteriorates seriously when the size of the device increases; (ii) the open circuit voltage of the photovoltaic device decreases with the increasing leakage current of GaN diodes; and (iii) low density nanotubes are detected in larger size GaN diodes, which is one of the important reasons for the large leakage of large size GaN diodes.
