Abstract
The growth of >100-μm-thick diamond layers adherent on aluminum nitride with low thermal boundary resistance between diamond and AlN is presented in this work. The thermal barrier resistance was found to be in the range of 16 m2·K/GW, which is a large improvement on the current state-of-the-art. While thick films failed to adhere on untreated AlN films, AlN films treated with hydrogen/nitrogen plasma retained the thick diamond layers. Clear differences in ζ-potential measurement confirm surface modification due to hydrogen/nitrogen plasma treatment. An increase in non-diamond carbon in the initial layers of diamond grown on pretreated AlN is seen by Raman spectroscopy. The presence of non-diamond carbon has minimal effect on the thermal barrier resistance. The surfaces studied with X-ray photoelectron spectroscopy revealed a clear distinction between pretreated and untreated samples. The surface aluminum goes from a nitrogen-rich environment to an oxygen-rich environment after pretreatment. A clean interface between diamond and AlN is seen by cross-sectional transmission electron microscopy.
Highlights
High electron mobility transistors (HEMTs) made from gallium nitride (GaN) are attractive for high-power and high-frequency applications.[1,2] Still, the full potential of GaNHEMT devices is yet to be realized due to less than effective thermal management
It has been shown that the average through-plane thermal conductivity of 100-μm-thick polycrystalline diamond films exceeds the thermal conductivity of silicon carbide (SiC) by >3 times, which is required for a step-change in GaN device thermal management.[14]
The AlN layer used in this study was grown on 150 mm Si substrates in an Aixtron close-coupled showhead metal−organic chemical vapor deposition (MOCVD) system
Summary
High electron mobility transistors (HEMTs) made from gallium nitride (GaN) are attractive for high-power and high-frequency applications.[1,2] Still, the full potential of GaN. For cost-effective, direct-growth wafer scale implementation of diamond as a thermal management layer, polycrystalline films need to be used This is due to the fact that it is possible to grow large-area wafer-scale polycrystalline diamond films, which is not the case for single crystals. There are other examples of plasma pretreatment on various other substrates for nucleation modification; in most cases, it has been done to enhance the nucleation density.[32−37] The growth of thick layers on as-received AlN was not possible initially when untreated as-grown AlN surfaces were used, but after surface treatment (hydrogen/nitrogen plasma exposure before seeding) it was possible to grow thick layers on AlN thin films. The thermal barrier resistance (TBReff) was measured using transient thermoreflectance measurements
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