Improvement of TE-polarized emission in type-Ⅱ InAlN–AlGaN/AlGaN quantum well

The optical properties of the type-Ⅱ lineup InxAl1-xN-Al0.59Ga0.41N/Al0.74Ga0.26N quantum well(QW) structures with different In contents are investigated by using the six-by-six K-P method.The type-Ⅱ lineup structures exhibit the larger product of Fermi-Dirac distribution functions of electron fc^n and hole(1-fv^Um) and the approximately equal transverse electric(TE) polarization optical matrix elements(|Mx|^2) for the c1-v1 transition.As a result, the peak intensity in the TE polarization spontaneous emission spectrum is improved by 47.45%-53.84% as compared to that of the conventional AlGaN QW structure.In addition, the type-Ⅱ QW structure with x^0.17 has the largest TE mode peak intensity in the investigated In-content range of 0.13-0.23.It can be attributed to the combined effect of |Mx|^2 and fc^n(1-fv^Um) for the c1-v1, c1-v2, and c1-v3 transitions.

Effect of surface plasmon coupling with radiating dipole on the polarization characteristics of AlGaN-based light-emitting diodes

The optical polarization characteristics of surface plasmon(SP)coupled Al Ga N-based light emitting diodes(LEDs)are investigated theoretically by analyzing the radiation recombination process and scattering process respectively.For the Al_(0.5)Ga_(0.5)N/Al/Al_(2)O_(3)slab structure,the relative intensity of TE-polarized and TM-polarized spontaneous emission(SE)rate into the SP mode obviously depends on the thickness of the Al layer.The calculation results show that TM dominated emission will be transformed into TE dominated emission with the decrease of the Al thickness,while the emission intensities of both TE/TM polarizations will decrease significantly.In addition,compared with TM polarized emission,TE polarized emission is easier to be extracted by SP coupling.For the Al_(0.5)Ga_(0.5)N/Al nano-particle structure,the ratio of transmittance for TE/TM polarized emission can reach~3.06,while for the Al free structure,it is only 1.2.Thus,the degree of polarization of SP coupled LED can be improved by the reasonable structural design.

Astronomical tuning and magnetostratigraphy of Neogene biogenic reefs in Xisha Islands, South China Sea

Biogenic reefs are one of two major depositional types in the South China Sea, and are constructed by coral, algae and bryozoa. The West Pacific is a major area of biogenic reef development and plays a critical role in the global carbon cycle. However, the lack of geochronological studies in previous works inhibits our understanding of their contributions. Herein, we conduct a cyclostratigraphic and magnetostratigraphic study on Neogene biogenic reefs using the XK–1 core that was drilled at the Shidao Island,Xisha(Paracel) Islands. The main findings of this study are:(1) the establishment of reliable magentostratigraphy for Ledong, Huangliu, Meishan and Sanya Formations;(2) the magnetic susceptibility variation can be inferred as growth index and tuned to the 405–ka long eccentricity cycle;(3) the astronomical geochronology suggests that the bottom ages for Ledong, Yinggehai, Huangliu, Meishan,and Sanya Formations are 2.2 Ma, 5.7 Ma, 10.4 Ma, 16.6 Ma, and 24.3 Ma, respectively; and (4) Earth's eccentricity and obliquity played predominant roles in biogenic reef establishment on orbital to tectonic timescales. Thus, the reported geochronology offers an opportunity to test the contributions of various factors and hypothesize their roles in the global carbon cycle in future.