The Effect of the Thermal Boundary Resistance on Self-Heating of AlGaN/GaN HFETs
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Internet Journal Nitride Semiconductor Research
The Effect of the Thermal Boundary Resistance on Self-Heating of AlGaN/GaN HFETs K.A. Filippov1 and A.A. Balandin1 1Nano-Device
Laboratory, Department of Electrical Engineering, University of California - Riverside,
(Received Friday, May 23, 2003; accepted Friday, July 25, 2003)
We have calculated the thermal boundary resistance at the GaN/SiC, GaN/sapphire and GaN/AlN interfaces in the diffuse mismatch approximation. The obtained values were then used to examine the effect of the thermal boundary resistance on heat diffusion in AlGaN/GaN heterostructure fieldeffect transistors. The results show that the thermal boundary resistance at the device layer interfaces can strongly influence the temperature rise in the device channel.
1
Introduction
The GaN materials system has established itself as being very important for the next generation of highpower density devices for optical, microwave, and radar applications [1] [2] [3] [4] [5]. At the same time, performance of these devices has been limited by self-heating [1] [6]. 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 [7] [8] [9]. We have previously shown that the temperature rise in AlGaN/ GaN heterostructure field-effect transistors (HFETs) is different for doped and undoped channel devices [10]. Recently, there have been experimental indications that the overall thermal resistance of AlGaN/GaN device structures is larger than the simple model estimates from the acoustic mismatch theory (AMT) [11]. One of the possible explanations of this fact can be a relatively large thermal boundary resistance (TBR) at the interface between GaN layer and the substrate. It has been experimentally determined in Ref. [11] that the TBR of the GaN/sapphire interface at 4.2K is about three orders of magnitude higher then AMT predictions. A strong effect of TBR on heat diffusion in device structures has been observed for other materials systems [12] [13] [14]. In this paper, we calculate TBR for GaN/SiC, GaN/ sapphire and GaN/AlN interfaces using the diffuse mis-
match model (DMM). The obtained values are then used to simulate heat diffusion and temperature rise in GaN/ AlGaN HFETs with characteristic biasing parameters. 2
Thermal Boundary Resistance
TBR is used to describe thermal transport across an interface and is defined as the inverse of thermal boundary conductivity
.
(1)
Here is a heat flow across an interface, A is an area and ∆T is the temperature difference between the two sides of the interface. In order to calculate TBR at the interfaces between different layers in a HFET structure we use the DMM approach, which assumes that the phonons incident on the interface wil
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