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Research On Simulation And Analysis Of Characteristic Of GaN Electronic Device With The Virtual Source Model

Posted on:2016-02-26Degree:MasterType:Thesis
Country:ChinaCandidate:Y T WangFull Text:PDF
GTID:2308330461988882Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
Ⅲ nitride heterostructure field-effect transistors are especially suitable for the application in the field of high frequency and high power due to their excellent properties. The current GaN HEMT devices fabrication is not self-aligned process, and this induces access regions in the structure of the devices. Therefore, there are access regions resistance both at the source and drain end (Rsa, Rda). So the series resistances at source and drain end (Rs, Rd) are composed of Rsa, Rda and ohmic contact resistances (Rsc, Rdc). The access resistance has an important influence on the output characteristics of the AlGaN/GaN HEMT. The phenomenon that the source access resistance Rsa increases nonlinearly with the increase of drain current limits the output transconductance, frequency characteristics, linearity and efficiency of the devices. Although the change mechanism of the source access resistance is very important, it is still unclear to us. So further studies are needed.AlN/GaN heterostructure has the highest concentration of two dimensional electron gas compared to other III nitride heterostructure since it possesses stronger spontaneous polarization and piezoelectric polarization. Because AlN barrier layer is relatively thinner, it is a great help to alleviate the short channel effect, so the AlN/GaN HEMT has more advantages in the fabrication of shorter gate devices. The carrier scattering mechanism in AlN/GaN HEMT has important influence on the output characteristics, so more comprehensive understanding of the scattering mechanism is crucial to the optimization of the device design and fabrication. Temperature has important effect on scattering mechanism, but the influence of the low temperature on the polarization Coulomb field scattering mechanism have never been studied before. Based on the above discussion, we did research on some aspects as follows.1. The study of the effect of polarization Coulomb field scattering on the source access resistance Rsa in AlGaN/GaN HEMT with application of Virtual Source model. The DC output characteristics are simulated by the application of the Virtual Source model. The source access resistance, intrinsic transconductance and the external tranconductance of the device at different voltages between the source and gate with the 5V voltage between the source and the drain are calculated through the application of the Virtual Source model. We found that as gate-source voltage increases, the drain current increases and the source resistance increases nonlinearly with the increase of the drain current. Moreover, the external transconductance decreases compared to the intrinsic transconductance. The electric field of AlGaN barrier at different position of the channel with different gate-source voltage are calculated. Considering two different factors which are the change of the polarization charge caused by the inverse piezoelectric effect and the change of temperature of the hot electron in the source access region with different gate-source voltages, the intensity of the polarization Coulomb field scattering first increases and then decreases as the gate voltage increases, and so does the source access resistance caused by the polarization Coulomb field. On the other hand, the strength of the electric field in the source access region significantly increases as the increase of drain current, and the temperature of the hot electron increased. So the intensity of the polarization optical phonon scattering increased rapidly. For a larger gate voltage condition, the increase of the source access resistance is mainly caused by the increase of the polarization optical phonon scattering.2. The polarization Coulomb field scattering in AIN/GaN HEMT at low temperature. The rectangle AIN/GaN HEMT are fabricated. The Capacitance-Voltage and Current-Voltage characteristics of the rectangular AIN/GaN HEMT are measured at different low temperatures. Using a quasi-two-dimensional model, we got the mobility-density characteristics of the two-dimensional electron gas modulated by the gate-source bias. And we got the mobility-density characteristics of the two-dimensional electron gas modulated by the drain-source bias at different low temperatures. As the temperature decreases from 250 K to 100 K the mobility difference modulate by the two different voltage modulations gets more significant, however, the difference at 10 K turns out to be smaller. We found that the polarization Coulomb field scattering is relatively enhanced as the temperature decreases from 250 K to 100 K and relatively reduced slightly at 10 K.
Keywords/Search Tags:GaN HEMT, two-dimensional electron gas, access resistance, polarization Coulomb field scattering
PDF Full Text Request
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