Reliability Concerns due to Self-Heating Effects in GaN HEMTs
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چکیده
Nitride semiconductors have emerged as a strong candidate for high power, high temperature and high frequency applications in the recent years [13]. The motivation for using this material system is clearly illustrated in Figure 1 below. It is important to emphasize that the strongest feature of the III-V materials is the heterostructure technology it can support quantum well, modulation-doped hetero interface, and heterojunction structure can all be made in this material system. Two dimensional electron densities on the order of 1013 cm-2 or higher can be achieved in GaN HEMTs owing to its large piezoelectric polarization charge that arises due to strain of the top layers. The piezoelectric polarization charge in these devices is about five times larger in comparison to GaAs HEMT structures. In addition, the spontaneous polarization, which is an inherent property of the material, is very high for GaN and AlN material systems. The electric fields produced by these charges are on the order of 2-5 MV/ cm. These high electric fields are responsible for the very high two-dimensional electron densities in these devices [4]. The major problem in GaN technology is the current collapse phenomenon [5]. The trapping of charge at the gate-drain surface leads to increase in the drain access resistance. This, in turn, leads to increase in conduction losses in high power switching applications. Significant amount of work, both experimental and theoretical, has been done to shed more light on the current collapse phenomena [6]. However, the role of self-heating effects on the gate edge electric field has not been examined. The goal of the present work is to evaluate the influence of self-heating towards the current collapse phenomenon in GaN HEMTs.
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تاریخ انتشار 2013