InAlN/GaN Schottky Diode Current Transport Mechanism

As the representative of wide band semiconductor material, GaN based semiconductor has superior physical characteristic and chemical stability and it can work in high frequency, high temperature and high radiation environment. It plays a more and more important role in high power electronic devices, especially in military and national defense area. The GaN epitaxy quality improves constantly during last few years, which promotes the performance of GaN device a lot. The InAlN/GaN heterojunction can be grown lattice matched with an Indium concentration of 17% and it can induce high density 2DEG with only spontaneous polarization effect.Due to the absence of piezoelectric polarization, InAlN/GaN heterojunction exhibits more reliable than AlGaN/GaN structure. In this paper, we researched the current transport mechanism of InAlN/GaN Schottky diodes.Firstly, we investigate the oxide layer on InAlN surface by XPS of 01s, which proves the existence of native oxide layer on InAIN surface. The Ohmic contact characteristic of the sample after BOE treatment indicates that BOE treatment is an effective method to remove the oxide layer. The C-V measurement showes high density 2DEG existing in the InAlN/GaN interface and Hall test in different temperature shows the carrier mobility decreases with increasing temperature while the 2DEG density increases first and then decrease with increasing temperature.Secondly, we investigate InAlN/GaN Schottky diodes forward-bias current transport mechanisms by temperature-dependent Ⅰ-Ⅴ measurements in the temperature range of 300-485 K. The Schottky barrier heights calculated by using the conventional thermionic-emission[TE) model are strongly positively dependent on temperature, which is in contrast to the negative-temperature-dependent characteristic of traditional semiconductor Schottky diodes. By fitting the forward-bias Ⅰ-Ⅴ characteristics using different current transport models, we find that the tunneling current model can describe generally the Ⅰ-Ⅴ behaviors in the entire measured range of temperature. Under the high forward bias, the traditional TE mechanism also gives a good fit to the measured Ⅰ-Ⅴ data, and the actual barrier heights calculated according to the fitting TE curve are 1.434 and 1.413 eV at 300 K for InAlN/GaN Schottky diodes on Si and the sapphire substrate, respectively, and the barrier height shows a slightly negative temperature coefficient.Finally, the temperature-dependent reverse Ⅰ-Ⅴ measurements were tested in the temperature range of 300-485 K. In this temperature range, the reverse leakage current was found to be in agreement with the Frenkel-Poole emission model. The main process in leakage current flow is the emission into or from dislocation-related trapped states or conduction along dislocation lines.