To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
129I/127I and 14C/12C depth profiles were compared for the surface 30-cm layer of soil samples (Andisols) collected from Shimokita Peninsula, northeastern Japan, in November 2005. The 129I/127I and 14C/12C profiles have a clear correlation, even taking into account that the data include samples collected from different sites with different surface histories. These results, and considering that 14C/12C can be regarded as a proxy of the original depth in stable soil, show the diversity of the 129I/127I ratio at the surface among the sites, indicating variations in the thicknesses of the layers recently removed. At one of the sampling sites (P003-1), the Δ14C value measures ∼110‰ near the surface, which is indicative of anthropogenic 14C produced by atmospheric testing of nuclear weapons during the late 1950s and early 1960s. This site has experienced no disturbances for at least the past 50 yr. The relatively high activity of 129I (0.8 mBq/kg) and the 129I/127I ratio (7 x 10–9) observed at the top layer of this site can be considered a “representative value” when considering the anthropogenic iodine transfer from the atmosphere to the ground. The observations also support 2 separate modes of 129I migration in the soil: i.e. “topmost quick diffusion” and “subsurface relatively slow migration process.” Even in the “subsurface relatively slow migration zone,” the 129I/127I ratio was still orders higher than the pre-anthropogenic natural level.
Low defect density a-plane GaN films were successfully grown by sidewall epitaxial lateral overgrowth (SELO) technique. Control of V/III ratio during the growth of GaN by metalorganic vapor phase epitaxy (MOVPE) was found to be very important to achieve a complete overgrowth on the SiO2 mask regions and atomically flat surface. The threading dislocation and stacking fault densities in the overgrown regions were lower than 106 cm−2 and 103 cm−1, respectively. The root mean square roughness was 0.09 nm. We also fabricated and characterized a-plane-GaN-based-light-emitting diodes (LEDs) using SELO technique. The light output power of the blue-green LED steeply increased with the decrease of threading dislocation density from 1010 cm−2 to 108 cm−2 and tended to saturate at lower dislocation densities.
The anisotropically biaxial strain in a-plane AlGaN on GaN is investigated by X-ray diffraction analysis of the heterostructure of AlGaN and GaN grown on r-plane sapphire. The AlGaN layer with a low AlN molar fraction or small thickness is coherently grown on the GaN layer both along the m-axis and c-axis. An increase in AlN molar fraction or thickness in AlGaN, results in a slight relaxation of AlGaN only in one direction due to tensile stress along the c-axis, which is caused by the underlying GaN layer during the growth. The cause of the relaxation of AlGaN in one direction is thought to be a large anisotropically biaxial stress.
Mg-doped p-type a-plane GaN films were grown on unintentionally doped a-plane GaN templates by metalorganic vapor phase epitaxy (MOVPE). The Mg concentration in a-plane GaN increased with increasing Mg source gas flow rate. A maximum hole concentration of 2.0 × 1018 cm-3 with a hole mobility of 4.5 cm2/Vs and resistivity of 0.7 Ω·cm were achieved. The activation ratio was 5.0 × 10-2. It was found that a maximum hole concentration in p-type a-plane GaN was higher than that in p-type c-plane GaN. The activation energy of Mg acceptors in p-type a-plane GaN with the maximum hole concentration was found to be 118 meV by temperature-dependent Hall-effect measurement.
Email your librarian or administrator to recommend adding this to your organisation's collection.