New Materials-Theory-Based Model for Output Characteristics of AlGaN/GaN Heterostructure Field Effect Transistors
- PDF / 81,204 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 93 Downloads / 199 Views
partment of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455, U.S.A. †
Electronic Science and Technology Division, U.S. Naval Research Laboratory, Washington, DC 20375, U.S.A. ABSTRACT A new model is used to examine the DC output characteristics of AlGaN/GaN heterostructure field effect transistors. The model is based on the charge-control/gradualchannel approximation and takes into account the non-linear current vs. voltage characteristics of the ungated AlGaN/GaN heterostructure channel regions. The model also includes thermal effects associated with device self-heating. For the power dissipation levels considered for many applications, the thermal degradation of the carrier drift velocity is shown to cause a negative output conductance in saturation. The temperature is incorporated self-consistently into the model through the field and temperature dependent mobility obtained from Monte Carlo transport simulations for electron transport in GaN. Calculated results presented for the DC output characteristics of several AlGaN/GaN field effect transistors show a strong dependence on the thermal properties of the substrate material. The substrate materials considered in this work are sapphire, SiC, AlN, and GaN. INTRODUCTION
The continuing improvement of group III-nitride compound semiconductor material quality has led to the demonstration of viable AlGaN/GaN heterostructure field effect transistors (HFETs) with widths up to 1mm1, suitable for high power amplifiers. For these applications self-heating of the device is important and, since the heat is conducted out of the active region through the substrate, the thermal properties of the substrates play a significant role in the device performance. The traditional sapphire substrate has shown itself to be inadequate and recent GaN-based power amplifier devices2 have explored new substrate materials. Alternative substrates include SiC, GaN, and AlN, which offer enhanced thermal conductivities. Power densities as large as 6.9 W/mm at 10GHz have been demonstrated for GaN-based devices on SiC3. Here, we present a comparison of the DC output characteristics of AlGaN/GaN HFETs on sapphire, SiC, AlN, and GaN. Monte Carlo transport calculations for electrons in GaN have yielded results for the degradation of the electron velocity with increasing temperature4. An HFET model in the framework of the charge-control/gradual-channel approximation and based on a parameterization of the calculated transport properties has been developed. Initial simplified versions of this model have been applied successfully to the analysis of DC current vs. voltage characteristics of gated5 and ungated6 AlGaN/GaN heterostructure
F99W11.15
devices fabricated on sapphire substrates. The model will be summarized only briefly here. A detailed description will be published separately7. The thermal properties of the substrates considered are included via temperaturedependent thermal impedances obtained from independent simulations of the twodimensional heat flow. Diss
Data Loading...
