some outstanding features, such as a high carrier mobility, [8][9][10] a high thermal conductivity, [11] flexibility, [12] and visible transparency. [13,14] Moreover, it can be used as a removable layer for the epitaxial growth of III-Ns, thus providing the foundation for a new field of transferable and flexible LEDs. [15,16] Recently, graphene has been used as a buffer layer for the van der Waals epitaxy growth of a GaN epilayer to overcome the substantial thermal expansion coefficient and in-plane lattice constant mismatch between the GaN epilayer and sapphire substrate (c-Al 2 O 3 ), which causes a significant strain in the GaN epilayer. However, because the graphene surface lacks dangling bonds, the nucleation of nitrides on graphene is restricted, and clusters are easily formed. [17,18] In this study, theoretical calculations using first-principles calculations based on density functional theory (DFT) were carefully conducted to further examine the formation mechanism of AlN and GaN on graphene. We found that AlN selectively grows on graphene, and we identified its optimal nucleation site. We obtained the adsorption probability of Al atoms at various positions on the graphene CC ring and found that the hollow of the complete graphene CC ring and the center of the broken graphene CC ring are the best adsorption positions under different states of the graphene. Based on this, we innovatively inserted an AlN composite nucleation layer between graphene and GaN, which was grown by metal organic chemical vapor deposition (MOCVD) using time-distributed and constant-pressure (TDCP) growth. The growth process for AlN is divided into three stages. Under the same pressure, different flow rates, and growth temperatures are used for each stage. By controlling the growth time at different flow rates, an AlN composite nucleation layer on graphene can be formed. By introducing the selective nucleation of an AlN composite layer and graphene, the biaxial stress of the GaN film was effectively released, leading to transferable and low density dislocations in the GaN film and the In 0.1 Ga 0.9 N/GaN multiple quantum well structures. Note that LEDs with an ultrahigh light output power (LOP) of 260.5 mW at a small current of 560 mA were achieved. Our study demonstrates a practical application of an AlN composite nucleation layer grown on graphene that may result in A transferable GaN epilayer is grown on an improved aluminum nitride (AlN)/graphene composite substrate. In this study, theoretical calculations using first-principles calculations based on density functional theory are carefully conducted to further examine the formation mechanism of AlN on graphene. AlN selectively grows on graphene via its optimal nucleation site, which leads to the selective nucleation of AlN on graphene via quasi-van der Waals epitaxy. Thus, an AlN composite nucleation layer is innovatively inserted between graphene and GaN, using the time-distributed and constant-pressure growth method by metal organic chemical vapor deposition. Moreover, a hi...

Defect behaviors in the degradation of AlGaN-based UV-C light emitting diodes (LEDs) under constant current stress have been intensively investigated in this work. It is found that both the reduction of the optical power and the increase in the leakage current are derived from the newly generated Ga vacancy (VGa) along dislocation, based on the evidence of a strong “yellow” emission peak at 515 nm in the photoluminescence spectra and an energy level of 0.25–0.38 eV. More importantly, the defect evolution behind it was determined through the deep level transient spectroscopy, secondary ion mass spectrometry measurements, and density functional theory. VGa is found to be generated by the departure of the unintentionally doped Mg from MgGa along dislocation in the Si-doped region. The high activity of the unintentionally doped Mg under electrical stress can be an essential factor in the degradation of UV-C LEDs. This study not only provides an in-depth insight into the electrical stress-induced degradation in UV-C LEDs but also sheds light on the way for fabricating AlGaN-based devices with high reliability.

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Temperature dependences of the polarized Raman scattering spectra in the backscattering configuration of the semipolar (112¯2) plane GaN thin film are analyzed in the range from 83 K to 563 K. The semipolar GaN film is cut at a tilted angle from polar GaN wafer grown by hydride vapor phase epitaxy. The spectral features of the frequency shift and linewidths of the Raman-active phonon modes Quasi-TO, E1 (TO), E2 (high), and Quasi-LO are prominently revealed, and the temperature coefficients corresponding to the lattice thermal expansion and phonon anharmonic effect, as well as defects and impurities in crystals, are well deduced by the theoretical equations. With the increasing temperature, the Raman scattering peaks would substantially shift to lower frequencies and the linewidths gradually broaden. Our studies will lead to a better understanding of the fundamental physical characteristics of the semipolar (112¯2) plane GaN film.

The graphene–blue phosphorus van deer Waals (vDW) heterojunction was studied by using density functional theory. Our calculations reveal that the intrinsic electronic structure of blue phosphorus and graphene is well preserved and forms an n-type schottky barrier at equilibrium state. With increasing of normal tensile strain, the n-type is well kept. With compressive strain, the Dirac cone of graphene gradually shifts from conduction band minimum to valance band maximum of blue phosphorus, leading a turning of schottky barrier from n-type to p-type, which indicates an effective way to tune the electronic structure of vDW heterojunction.