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Square microdisks with round corners are fabricated using a standard GaN-based blue LED on Si substrates. Whispering gallery-like modes in the square microdisks are investigated by finite-difference time-domain simulation. The simulation results reveal that the round corners in square microdisks can substantially suppress the number of light propagation paths and further reduce the number of optical modes. A confocal micro-photoluminescence is performed to analyze the optical properties of the square microdisks at room temperature. The single-mode dominant resonant emission is obtained in the square microdisk with corner radius of 1.5 μm.

Two-inch Ga2O3 films with ( )-orientation are grown on c-sapphire at 850–1050°C by hydride vapor phase epitaxy. High-resolution x-ray diffraction shows that pure β-Ga2O3 with a smooth surface has a higher crystal quality, and the Raman spectra reveal a very small residual strain in β-Ga2O3 grown by hydride vapor phase epitaxy compared with bulk single crystal. The optical transmittance is higher than 80% in the visible and near-UV regions, and the optical bandgap energy is calculated to be 4.9 eV.

GaN nanorods are fabricated using inductively coupled plasma etching with Ni nano-island masks. The poly [2-methoxy-5-(2-ethyl)hexoxy-1,4-phenylenevinylene] (MEH-PPV)/GaN-nanorod hybrid structure is fabricated by depositing the MEH-PPV film on the GaN nanorods by using the spin-coating process. In the hybrid structure, the spatial separation is minimized to achieve high-efficiency non-radiative resonant energy transfer. Optical properties of a novel device consisting of MEH-PPV/GaN-nanorod hybrid structure is studied by analyzing photoluminescence (PL) spectra. Compared with the pure GaN nanorods, the PL intensity of the band edge emission of GaN in the MEH-PPV/GaN-nanorods is enhanced as much as three times, and the intensity of the yellow band is suppressed slightly. The obtained results are analyzed by energy transfer between the GaN nanorods and the MEH-PPV. An energy transfer model is proposed to explain the phenomenon.

Microstructures of GaN buffer layers grown on Si (111) substrates using rapid thermal process low-pressure metalorganic chemical vapor deposition are investigated by an atomic force microscope (AFM) and a high-resolution transmission electron microscope (HRTEM). AFM images show that the islands appear in the GaN buffer layer after annealing at high temperature. Cross-sectional HRTEM micrographs of the buffer region of these samples indicate that there are bunched steps on the surface of the Si substrate and a lot of domains in GaN misorienting each other with small angles. The boundaries of those domains locate near the bunched steps, and the regions of the film on a terrace between steps have the same crystal orientation. An amorphous-like layer, about 3 nm thick, can also be observed between the GaN buffer layer and the Si substrate.

By using a simple method to factorize the recursion operator, the inverse recursion operator of the variable coefficient KdV equation is exhibited explicitly. Three new sets of symmetries of the variable coefficient KdV equation are given in addition to the known K symmetries and τ symmetries. Starting from these three sets of symmetries, we obtained three hierarchies of the variable coefficient KdV integro-differential equations.

A novel fishing rod-shaped GaN nanorod is successfully fabricated through a new method by using the two-step growth technology. This growth method is applicable to continuous synthesis and is able to produce a large number of single-crystalline GaN nanorods with a relatively high purity and at a low cost. X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy are used to characterize the as-synthesized nanorods. The results show that most of the nanorods consist of a main rod and a top curved thread. It is single-crystal GaN with hexagonal wurtzite structure. The representative photoluminescence spectrum at room temperature exhibits a strong UV light emission band centered at 370.8 nm. Furthermore, a possible two-stage growth mechanism of the fishing rod-shaped GaN nanorod is also briefly discussed.

We report on the photoluminescent characteristics of InGaN/GaN multiple quantum well (MQW) nanorod arrays with high internal quantum efficiency. The InGaN/GaN MQWs are grown by metalorganic chemical vapor deposition on c-plane sapphire substrates, and then the MQW nanorod arrays are fabricated by using inductively coupled plasma etching with self-assembled Ni nanoparticle mask with low-damage etching technique. The typical diameter of the nanorods is from 200 nm to 300 nm and the length is around 800 nm, which almost is dislocation free. At room temperature, an enhancement of 3.1 times in total integrated photoluminescence intensity is achieved from the MQW nanorod arrays, in comparison to that of the as-grown MQW structure. Based on the temperature-dependent photoluminescence measurements, the internal quantum efficiency of the nanorod structure is 59.2%, i.e., 1.75 times of as-grown MQW structure (33.8%). Therefore, the nanorod structure with a significant reduction of defects can be a very promising candidate for highly efficient light emitting devices.

Roughened surfaces of light-emitting diodes (LEDs) provide substantial improvement in light extraction efficiency. By preparing the self-assemble nanoporous Ni template through rapid annealing of a thin Ni film, followed by a low damage dry etching process, a p-side-up LED with a roughened surface has been fabricated. Compared to a conventional LED with plane surface, the light output of LEDs with nanoporous p-GaN surface increases up to 71% and 36% at applied currents of 1 mA and 20 mA, respectively. Meanwhile, the electrical characteristics are not degraded obviously after surface roughening.

The influence of dry etching damage on the internal quantum efficiency of InGaN/GaN nanorod multiple quantum wells (MQWs) is studied. The samples were etched by inductively coupled plasma (ICP) etching via a self-assembled nickel nanomask, and examined by room-temperature photoluminescence measurement. The key parameters in the etching process are rf power and ICP power. The internal quantum efficiency of nanorod MQWs shows a 5.6 times decrease substantially with the rf power increasing from 3 W to 100 W. However, it is slightly influenced by the ICP power, which shows 30% variation over a wide ICP power range between 30 W and 600 W. Under the optimized etching condition, the internal quantum efficiency of nanorod MQWs can be 40% that of the as-grown MQW sample, and the external quantum efficiency of nanorod MQWs can be about 4 times that of the as-grown one.

InxGa1−xN alloys with low indium composition x in the range 0.13 ≤ x ≤ 0.23 are systematically studied mainly based on a Raman scattering technique. Scanning electron microscopy and x-ray diffraction results show that our samples can be divided into two groups: pseudomorphic (0.13 ≤ x ≤ 0.16) and relaxed (0.18 ≤ x ≤ 0.23). The prominent enhancement of A1 longitudinal-optical (LO) mode is found with 325 nm laser excitation. For pseudomorphic samples, the frequencies of A1 (LO) phonons agree well with the theoretical predictions, which verifies that the samples are fully strained. For relaxed InxGa1−xN samples, a linear dependence of the A1 (LO) mode frequency is obtained: Ω0(x) = (740.8 ± 3.3) − (143.1 ± 16.0)x, which is the evidence of one-mode behavior in InxGa1−xN ternary alloys. Residual strains in these partially relaxed samples are also evaluated.

Homo-epitaxial layers are successfully grown on Si-face 4° off-axis 4H-SiC substrates using the horizontal hot-wall chemical vapor deposition system. The smooth surface without morphological defects is obtained by the optimized in situ etching process and growth temperature. Schottky diodes fabricated on the epilayer present a typical I—V characteristic. This is the first report of Schottky diodes fabricated on 4° off-axis 4H-SiC substrates made in China.

Blue-red complex light emitting InGaN/GaN multi-quantum well (MQW) structures are fabricated by metal organic chemical vapor deposition (MOCVD). The structures are grown on a 2-inch diameter (0001) oriented (c-face) sapphire substrate, which consists of an approximately 2-μm-thick GaN template and a five-period layer consisting of a 4.9-nm-thick In0.18Ga0.82N well layer and a GaN barrier layer. The surface morphology of the MQW structures is observed by an atomic force microscope (AFM), which indicates the presence of islands of several tens of nanometers in height on the surface. The high resolution x-ray diffraction (XRD) θ/2θ scan is carried out on the symmetric (0002) of the InGaN/GaN MQW structures. At least four order satellite peaks presented in the XRD spectrum indicate that the thickness and alloy compositions of the individual quantum wells are repeatable throughout the active region. Besides the 364 nm GaN band edge emission, two main emissions of blue and amber light from these MQWs are found, which possibly originate from the carrier recombinations in the InGaN/GaN QWs and InGaN quasi-quantum dots embedded in the QWs.

AlGaN/GaN-based planar Schottky barrier diodes with various spacings between ohmic and Schottky contacts are fabricated without any edge termination. The reverse leakage current of the devices quickly saturates at low reverse bias when the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface is fully depleted. The corresponding breakdown voltage is found to follow a linear dependence on contact spacing and exceeds 1100 V at a contact spacing of 20 μm, yielding a high V2BR/RON value of > 280 MWcm−2. The observations are tentatively explained by a "natural super-junction" theory, in which ionized surface states at front surface of the AlGaN barrier have to be neutralized by reverse surface leakage current from the Schottky electrode.