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The Research Of Device Characteristics For AlGaN/GaN Polarization-doped Field-effect Transistors

Posted on:2016-01-21Degree:MasterType:Thesis
Country:ChinaCandidate:W J ShiFull Text:PDF
GTID:2308330461990586Subject:Microelectronics and Solid State Electronics
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Recently GaN-based materials which have broad applications in the the field of high-temperature,high-frequency, high-power devices have been the focus of intense research. As one of the most important members of the 3rd generation semiconductors, they have many advantages such as, wide band gap, high breakdown electric field, high electron saturated velocity, high thermal conductivity and excellent chemical stability. AlGaN/GaN HFETs based on AlGaN/GaN heterostructures have many excellent performances, such as high transconductance, high saturated current, high cutoff frequency and high breakdown voltage.The study on the AlGaN/GaN HFETs have reached the industrialization and practical level since the first AlGaN/GaN HFET has been made in 1993. However, there are still many problems, such as, high efficiency hole doping in GaN-based materials, the development of high Al content AlGaN/GaN heterostructures etc. Recently, it was found that graded AlGaN provides a solution to these problems because of its excellent characteristics. Therefore, it is very important to study AlGaN/GaN PolFETs. Based on this, we did research on some aspects as follows.1. Research on the operating principle of the AlGaN/GaN PolFETs. The operating principle of devices is the basis of device analysis. We explained the formation of 3DEG by understanding the structure of the device. And we analysed the operating principle of devices combining with the operating principle of MESFETs. In addition, we analysed the scattering mechanism of 3DEG electron mobility in AlGaN/GaN PolFETs.2. Research on the computational model of 3DEG electron mobility in AlGaN/GaN PolFETs. Research of 3DEG electron mobility in AlGaN/GaN PolFETs is the foundation of device analysis. On the basis of the above study, we analysed the computational model of 3DEG electron mobility in AlGaN/GaN PolFETs with low electric field.3. Research on the 3DEG electron mobility of AlGaN/GaN PolFETs with different sizes, (a) Research on the 3DEG electron mobility of AlGaN/GaN PolFETs with same drain-source distance. We made two types of AlGaN/GaN PolFET devices with drain-source distance of 100 μm,60 μm. The devices with drain-source distance of 100 μm have two types,one is devices with the side-Ohmic contacts,one is devices with the normal-Ohmic contacts. The distribution of 3DEG concentration for each device was calculated using the measured C-V curves and the C-V method of testing the distribution of impurity. The average 3DEG density under different gate biases was obtained by integrating C-V curves, and then we obtained the average 3DEG concentration under different gate biases for each device. The 3DEG electron mobility at the source-drain bias of 100mV under different gate biases for each device was calculated using the measured Ⅰ-Ⅴ characteristics and the computational model of 3DEG electron mobility in AlGaN/GaN PolFETs. We explained these phenomena with polarization Coulomb field scattering, LO phonon scattering, Alloy disorder scattering. It was found that the influence of polarization Coulomb field scattering in AlGaN/GaN PolFETs is weak than that in HFETs. Polarization Coulomb field scattering has big influence on devices with small gate area.(b) Research on the 3DEG electron mobility of AlGaN/GaN PolFETs with different drain-source distance. The devices with a gate-source and gate-drain distance of 10 μm,40 μm were made. The distribution of 3DEG concentration and the average 3DEG density under different gate biases for each device were calculated in the same way. The 3DEG electron mobility at the source-drain bias of 100mV under different gate biases for each device was calculated using the measured Ⅰ-Ⅴ characteristics and the computational model of 3DEG electron mobility in AlGaN/GaN PolFETs. It is shown that polarization Coulomb field scattering has big influence on devices with small gate area.(c) Research on the 3DEG electron mobility of AlGaN/GaN PolFETs with offset gate. The devices with drain-source distance of 40 μm and gate length of 8 μm were made. It is shown that polarization Coulomb field scattering may be correlated with the ratio of the gate length to the drain-source distance.
Keywords/Search Tags:AlGaN/GaN PolFETs, three-dimensional electron gas, electron mobility, Alloy disorder scattering, polarization Coulomb field scattering, polarization effect
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