| dc.description.abstract | In this study, AlGaN / GaN HEMT structures on the high-resistance AlN buffer layer and the conventional GaN buffer layer were grown, respectively. The planar Schottky diodes were then fabricated on these structures. From the I-V measurement, the results indicate the device with high-resistance AlN buffer layer not only substantially promote the breakdown voltage but also keep the low leakage current density. Therefore, in this study we discussed in detail about the factors of SBDs characteristics on different buffer layers, and further analyzed the mechanism of leakage current.
In the analysis of material quality, according to the x-ray diffraction GaN (002) rocking curve shows that AlN buffer layer can effectively reduce the screw-type dislocation density of epitaxial materials, thus reducing the leakage current. Besides, the etching pits density (EPD) is also calculated that the dislocation density of the above epitaxial structure reduced to about 3.2x107 cm-2, which is about an order lower compared to the epitaxial material grown on the GaN buffer layer.
In the analysis of leakage current, the leakage current in the buffer layer and the AlGaN barrier layer are discussed, respectively. In the discussion, the resistance of the AlN buffer layer is about six orders greater than that of the GaN buffer layer, indicating that the AlN buffer layer has the characteristic of low-leakage current; in addition, temperature-dependent current-voltage (I-V) measurement and frequency-dependent capacitance-voltage (C-V) measurement are used to analyze the mechanism of leakage current. The results show that the primary source for the leakage current during the voltage of 0 V~ - 6 V is the AlGaN barrier layer while the leakage current is dominated by the quality of buffer layer below -6 V. To further discussion, defect energy levels in AlGaN barrier are quantified by the leakage current model of Frenkel-Poole emission (F-P emission).
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