Influence of Dopants on the Thermal Conductance of GaN–Sapphire Interface

Abstract

Transient thermoreflectance (TTR) was used to characterize the interface thermal conductance ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</i> ) between GaN and sapphire at room temperature. Undoped, n-type, and p-type GaN films are grown by metal-organic chemical vapor deposition (MOCVD) on (0001) sapphire substrate. An In film pressed onto the GaN surface is used as a transducer and to measure the TTR signal. The TTR signal is also used to characterize the attenuation of acoustic waves and the surface roughness of the sapphire wafer. Results are modeled using 1-D heat conduction, and the value of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</i> is determined. Results indicate that the value of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</i> of the In-GaN interface remains between 18 and 28 MWm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The value of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</i> for the interface between undoped or n-type GaN and sapphire is low at 8 MWm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , and that between p-type GaN and sapphire is lower at 3 MWm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The absence of good atomic level contact between pressed In and GaN is considered responsible for the low value of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</i> . High concentration of Mg dopant atoms in the p-type GaN films at the interface, sapphire wafer with rough surface, and high dislocation density are also considered responsible for the lower value of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</i> . The results indicate poor thermal energy dissipation, higher device temperature, reduced transconductance, and related device performance.