Thermal Boundary Resistance and Heat Diffusion in AlGaN/GaN HFETs
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C3.57.1
Thermal Boundary Resistance and Heat Diffusion in AlGaN/GaN HFETs
Konstantin A. Filippov and Alexander A. Balandin Nano-Device Laboratory Department of Electrical Engineering University of California - Riverside Riverside, California 92521 ABSTRACT We theoretically investigate the thermal boundary resistance and heat diffusion in AlGaN/GaN heterostructure field-effect transistors. Our calculations based on the diffuse mismatch model show that the thermal boundary resistance at the interface between GaN and SiC can strongly influence the temperature rise in the device channel.
I. INTRODUCTION GaN materials system has established itself as very important for next generation of high-power density devices for optical, microwave, and radar applications [1-3]. At the same time, performance of these devices has been limited by self-heating [1, 4]. Thus, accurate modeling of heat diffusion and self-heating effects in AlGaN/GaN heterostructures and device optimization based on such modeling become crucial for further development of nitride technology. Simulation of heat diffusion in GaN and related materials is complicated by large discrepancy in the reported experimental thermal conductivity data and its dependence on defects and dislocations [5-7]. We have previously shown that the temperature rise in AlGaN/GaN heterostructure field-effect transistors (HFETs) is different for the doped and undoped channel devices [8]. Recently there have been experimental indications that the overall thermal resistance of AlGaN/GaN device structures (either on SiC or sapphire) is larger than the simple model estimates. One of the possible explanations of this fact can be noticeable thermal boundary resistance (TBR) at the interface between GaN layer and the substrate. A strong effect of TBR on heat diffusion has been observed for other materials systems [9-11]. In this paper we calculate TBR using the diffuse mismatch model (DMM) and, then, simulate heat diffusion and temperature rise for a typical devices structure.
II. THERMAL BOUNDARY RESISTANCE TBR is used to describe thermal transport across an interface and is defined as the inverse of thermal boundary conductivity −1 Q& R Bd = (1) . A ⋅ ∆T
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Here Q& is a heat flow across an interface, A is an area and ∆T is temperature difference between the two sides of the interface. In order to calculate TBR at the interfaces between different layers in HFET structure we use DMM approach, which assumes that the phonons incident on the interface will all undergo diffuse scattering [12]. In the framework of this model TBR can be written as −1
ω1 1 dN1, j (ω , T ) dω , = ⋅ ∑ν 1, j ⋅ Γ1, j ⋅ ∫ hω dT 2 j 0 Debye
RBd
(2)
where N1, j (ω , T ) =
ω2 hω − 1 2π 2ν 13, j exp k BT
.
(3)
Here k B is Boltzmann’s co
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