The thermal expansion of wurtzite AlN bulk crystals grown by physical vapor transport was studied by high resolution x-ray diffraction in a temperature range from 20 to 1250 K. The temperature dependence of the derived anisotropic thermal expansion coefficients along the a- and c-directions could be well described over the entire temperature range within both the Debye model and the Einstein model. In comparison to GaN, larger expansion coefficients and higher characteristic temperatures have been found. The resulting thermal mismatch of AlGaN/GaN heterostructures are presented.
We measured the lattice constants of bulk aluminum nitride crystals at various temperatures by high resolution X-ray diffraction. By the use of a high temperature chamber and a X-ray cryostat a temperature regime from 20 to 1210 K was available. Furthermore, the measured data were fitted by Einstein-and Debye models which yield reliable parameters for the calculation of the thermal expansion coefficients of AlN.
Amorphous gallium oxide thin films were grown by plasma-enhanced atomic layer deposition on (100) silicon substrates from trimethylgallium Ga(CH3)3 precursor and oxygen plasma. At 200 °C, the growth per cycle is in the range of 0.65–0.70 Å for O2 plasma exposure times ranging from 3 up to 30 s during each cycle. The effect of O2 plasma exposure times on the interfacial SiOx regrowth and the electrical properties was investigated. In situ spectroscopic ellipsometry shows that the SiOx regrowth occurs during the first three cycles and is limited to 0.27 nm for plasma times as long as 30 s. Increasing the O2 plasma exposure during each ALD cycle leads to a drastic decrease in the leakage current density (more than 5 orders of magnitude for 30 nm films), which is linked to the suppression of oxygen vacancy states as evidenced by spectroscopic ellipsometry. Interestingly, an increase in the dielectric constant with increasing O2 plasma exposure time is observed, reaching a value of εr∼14.2, larger than that of single crystalline β-Ga2O3. This study highlights the crucial role of oxygen plasma exposure time in the control and tuning of the electrical properties of amorphous gallium oxide films.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.