ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
We have measured high resolution thermal conductivity (κ) and Raman spectra {E2 mode [high frequency], A1 mode [longitudinal optical (LO)], and high frequency LO-plasmon coupled mode [LPP+]} at 300 K of three series of n-GaN/sapphire (0001) samples fabricated by hydride vapor phase epitaxy (HVPE). The former was determined with a scanning thermal microscope while the latter was obtained using a micro-Raman system, both having a spatial resolution of (approximate)2–3 μm. For all three sets of samples the thermal conductivity decreased linearly with log n, about a factor of two decrease in κ for every decade increase in n. Also, we found a correlation between film thickness and improved thermal conductivity. Furthermore, κ(approximate)1.95 W/cm K for one of the most lightly doped samples ((approximate)6.9×1016 cm−3), higher than previously reported κ(approximate)1.7–1.8 W/cm K on lateral epitaxial overgrown (LEO) material with n(approximate)(1–2)×1017 cm−3 [V. M. Asnin et al., Appl. Phys. Lett. 75, 1240 (1999)], κ=1.55 W/cm K on LEO samples using a third-harmonic technique [C. Y. Luo et al., Appl. Phys. Lett. 75, 4151 (1999)], and κ(approximate)1.3 W/cm K on a HVPE sample [E. K. Sichel and J. I. Pankove, J. Phys. Chem. Solids 38, 330 (1977)]. The carrier concentration dependence of κ is similar to that of other semiconductors in a comparable temperature range. On a log–log scale the linewidth of the observed E2 Raman mode remained constant up to n(approximate)1×1018 cm−3 and then increased linearly. The carrier concentration obtained from the LPP+ mode is less than the Hall effect determination. This is probably due to the fact that the latter measures n in both the epilayer and GaN/sapphire interfacial region [D. C. Look and R. J. Molnar, Appl. Phys. Lett. 70, 3377 (1997); W. Götz et al., Appl. Phys. Lett. 72, 1214 (1998)] while the Raman signal is primarily from the epilayer. © 2000 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1289072
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