We report a study of nitrogen incorporation in GaAs using a N rf plasma source. The N composition can be increased by lowering the growth temperature. X-ray diffraction shows no phase separation. Optical absorption measurements indicate that GaNxAs1−x is a direct band-gap material in the N composition range studied (x⩽14.8%), rather than a semimetal, contrary to theoretical predictions based on Van Vechten’s model. Analyzing the N composition dependence of the band-gap energy of the alloy indicates a composition-dependent bowing parameter, consistent with the first-principles supercell calculations [L. Bellaiche, S. H. Wei, and A. Zunger, Phys. Rev. B 54, 17 568 (1996)].
Methylammonium lead halide perovskite nanocrystals offer attractive optoelectronic properties but suffer from fast degradation in the presence of water. In contradiction to this observation, we demonstrate the possibility of a direct aqueous synthesis of CH NH PbX (X=Br or Cl/Br) nanocrystals through the reaction between the lead halide complex and methylamine when the pH is maintained in the range of 0-5. Under these synthetic conditions, the positively charged surface of the perovskite nanocrystals and the proper ionic balance help to prevent their decomposition in water. Additional surface capping with organic amine ligands further improves the photoluminescence quantum yield of the perovskite nanocrystals to values close to 40 %, ensures their stability under ambient conditions for several months, and their photoluminescence performance under continuous 0.1 W mm 405 nm light irradiation for over 250 hours.
Lead halide perovskites
are emerging as promising candidates for
high-efficiency light-emitting diode (LED) applications because of
their tunable band gaps and high quantum yield (QY). However, it remains
a challenge to obtain stable red emitting materials with high QY.
Herein, we report a facile and convenient hot-injection strategy to
synthesize Mn-doped two-dimensional (2D) perovskite nanosheets. The
emission peak can be tuned from 597 to 658 nm by manipulating the
crystal field strength. In particular, a QY as high as 97% for 2D
perovskite is achieved. The as-prepared perovskite also possesses
excellent stability, whose emission property can be maintained for
almost one year. A monochrome LED is further fabricated by employing
the as-prepared perovskite as phosphor, which also shows high long-term
stability. We believe that these highly efficient and stable perovskites
will open up new opportunities in LED applications.
In this report, we propose to enhance the hole injection efficiency by adjusting the barrier height of the p-type electron blocking layer (p-EBL) for ∼273 nm deep ultraviolet light-emitting diodes (DUV LEDs). The barrier height for the p-EBL is modified by employing a p-Al 0.60 Ga 0.40 N/ Al 0.50 Ga 0.50 N/p-Al 0.60 Ga 0.40 N structure, in which the very thin Al 0.50 Ga 0.50 N layer is able to achieve a high local hole concentration, which is very effective in reducing the effective barrier height of the p-EBL for holes. More importantly, besides the thermionic emission, such a p-EBL structure can also favor a strong intraband tunneling process for holes. As a result, we can obtain a more efficient hole injection into the quantum wells, leading to a remarkably improved optical power for the DUV LED with the proposed p-EBL architecture.
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