The heat transport mechanisms in superlattices are identified from the cross-plane thermal conductivity Λ of (AlN)x-(GaN)y superlattices measured by time-domain thermoreflectance. For (AlN) 4.1 nm-(CaN)55nm superlattices grown under different conditions, A varies by a factor of two; this is attributed to differences in the roughness of the AlN/CaN interfaces. Under the growth condition that gives the lowest Λ, Λ Of(AlN)4 nm -(GaN)y superlattices decreases monotonically as y decreases, Λ = 6.35 W m -1 K-1 at y = 2.2 nm, 35 times smaller than A of bulk CaN. For long-period superlattices (y > 40nm), the mean thermal conductance C of AlN/GaN interfaces is independent of y, G ≈ 620 MW m-2 K -1. For y < 40 nm, the apparent value of C increases with decreasing y, reaching C » 2 CW m-2 K-1 at y < 3 nm. MeV ion bombardment is used to help determine which phonons are responsible for heat transport in short period superlattices. The thermal conductivity of an (AlN)4.1 nm-(CaN)4.9 nm superlattice irradiated by 2.3 MeVAr ions to a dose of 2 × 1014 ions cm-2 is reduced by <35%, suggesting that heat transport in these short-period superlattices is dominated by long-wavelength acoustic phonons. Calculations using a Debye-Callaway model and the assumption of a boundary scattering rate that varies with phonon-wavelength successfully capture the temperature, period, and ion-dose dependence of A.
|Original language||English (US)|
|Number of pages||6|
|Journal||Advanced Functional Materials|
|State||Published - Feb 24 2009|
ASJC Scopus subject areas
- Materials Science(all)
- Condensed Matter Physics