晶格匹配In_(0.17)Al_(0.83)N/GaN异质结电容散射机制

制备了晶格匹配In_(0.17)Al_(0.83)N/GaN异质结圆形平面结构肖特基二极管,通过测试和拟合器件的电容-频率曲线,研究了电容的频率散射机制.结果表明:在频率高于200 kHz后,积累区电容随频率出现增加现象,而传统的电容模型无法解释该现象.通过考虑漏电流、界面态和串联电阻等影响对传统模型进行修正,修正后的电容频率散射模型与实验结果很好地符合,表明晶格匹配In_(0.17)Al_(0.83)N/GaN异质结电容随频率散射是漏电流、界面态和串联电阻共同作用的结果.

Capacitance scattering mechanism in lattice-matched In0.17Al0.83N/GaN heterojunction Schottky diodes

In order to study the frequency scattering mechanism of capacitance in latticematched In_0.17Al_0.83N/GaN high electron mobility transistors (HEMTs), the latticematched In_0.17Al_0.83N/GaN heterojunction Schottky diodes with circular planar structure, which have equivalent capacitance characteristics to those of HEMTs, are fabricated and tested in this paper. The experimental curves of capacitance-voltage characteristics at different frequencies show that the capacitance of the accumulation area decreases gradually with the increase of frequency at low frequency, which accords with the capacitance frequency scattering characteristics of traditional HEMT devices. However, when the frequency is higher than 200 kHz, the capacitance of the accumulation area increases rapidly with frequency increasing, which cannot be explained by the traditional capacitance model. By comparing the reverse current and capacitance characteristics of latticematched In_0.17Al_0.83N/GaN Schottky diodes, it is observed that the saturation behavior of the reverse leakage current is clearly associated with full depletion of the two-dimensional electron gas at the InAlN/GaN interface, which is indicated by the rapid drop of the diode capacitance. This observation suggests that the large reverse leakage current of the lattice-matched In_0.17Al_0.83N/GaN Schottky diode, which reaches up to 10^-4 A, should has a direct influence on the capacitance scattering. By considering the influence of leakage current, interface state and series resistance comprehensively, the capacitance frequency scattering model is modified based on the traditional model. Using various models to fit the experimental capacitance-frequency data, the results from the modified model agree well with the experimental results. According to the parameters obtained by fitting, the density and the time constant of interface defects in latticematched In_0.17Al_0.83N/GaN Schottky diodes, determined by equivalent interface capacitance and resistance, are about 1.66×10¹⁰ cm^-2·eV^-1 and 2.65μs, respectively. According to the values reported in the literature, it is suggested that the modified capacitance frequency scattering model should be reasonable for explaining the capacitance scattering phenomenon in accumulation area. In conclusion, we believe that the capacitance of latticematched In_0.17Al_0.83N/GaN Schottky diode scatters is a joint result of leakage current, interface state and series resistance. The interface defects in In_0.17Al_0.83N/GaN Schottky diodes usually have a great influence on frequency and power characteristics of devices, a correct explanation for the frequency scattering mechanism of capacitance is the basis for determining the locations and sources of defects in Ⅲ nitride devices.