Dependencies of surface plasmon coupling effects on the p-GaN thickness of a thin-p-type light-emitting diode.

The high performance of a light-emitting diode (LED) with the total p-type thickness as small as 38 nm is demonstrated. By increasing the Mg doping concentration in the p-AlGaN electron blocking layer through an Mg pre-flow process, the hole injection efficiency can be significantly enhanced. Based on this technique, the high LED performance can be maintained when the p-type layer thickness is significantly reduced.

Multi-mechanism efficiency enhancement in growing Ga-doped ZnO as the transparent conductor on a light-emitting diode.

The combined effects of a few mechanisms for emission efficiency enhancement produced in the overgrowth of the transparent conductor layer of Ga-doped ZnO (GaZnO) on a surface Ag-nanoparticle (NP) coated light-emitting diode (LED), including surface plasmon (SP) coupling, current spreading, light extraction, and contact resistivity reduction, are demonstrated. With a relatively higher GaZnO growth temperature (350 °C), melted Ag NPs can be used as catalyst for forming GaZnO nanoneedles (NNs) through the vapor-liquid-solid growth mode such that light extraction efficiency can be increased. Meanwhile, residual Ag NPs are buried in a simultaneously grown GaZnO layer for inducing SP coupling.

Regularly patterned multi-section GaN nanorod arrays grown with a pulsed growth technique.

The growth of regularly patterned multi-section GaN nanorod (NR) arrays based on a pulsed growth technique with metalorganic chemical vapor deposition is demonstrated. Such an NR with multiple sections of different cross-sectional sizes is formed by tapering a uniform cross section to another through stepwise decreasing of the Ga supply duration to reduce the size of the catalytic Ga droplet. Contrast line structures are observed in either a scanning electron microscopy or transmission electron microscopy image of an NR.

Multi-section core-shell InGaN/GaN quantum-well nanorod light-emitting diode array.

The growth of a two-section, core-shell, InGaN/GaN quantum-well (QW) nanorod- (NR-) array light-emitting diode device based on a pulsed growth technique with metalorganic chemical vapor deposition is demonstrated. A two-section n-GaN NR is grown through a tapering process for forming two uniform NR sections of different cross-sectional sizes. The cathodoluminescence (CL), photoluminescence (PL), and electrolumines-cence (EL) characterization results of the two-section NR structure are compared with those of a single-section NR sample, which is prepared under the similar condition to that for the first uniform NR section of the two-section sample.

Thermally induced variations of strain condition and emission behavior in flat and bendable light-emitting diodes on different substrates.

The emission behaviors of four light-emitting diodes (LEDs) of different substrate structures, including a lateral LED grown on sapphire, a vertical LED wafer-bonded onto Si (111), a bendable LED Ag-epoxied onto a flat metal, and another bendable LED Ag-epoxied onto a metal of a curved surface, under different duty cycles of current injection are compared. Their different variation trends of emission behavior with injection duty cycle are attributed to the different thermally-induced strain conditions in the epitaxial layers, which are controlled by their substrate structures, in increasing injection duty cycle or current level. The results of Raman scattering measurements during LED operation show that a stronger tensile strain is generated under heating for reducing the quantum-confined Stark effect and hence increasing emission efficiency when the epitaxial layer is not tightly bonded onto a hard substrate.

Modulation behaviors of surface plasmon coupled light-emitting diode.

The modulation bandwidths of the light-emitting diodes (LEDs) of different mesa sizes with and without surface plasmon (SP) coupling effect are compared. Due to the significant increase of carrier decay rate, within the size range of LED square-mesa from 60 through 300 micron and the injected current-density range from 139 through 1667 A/cm², the SP coupling can lead to the enhancement of modulation bandwidth by 44-48%, independent of the variations of LED mesa size or injected current level. The enhancement ratios of modulation bandwidth of the samples with SP coupling with respect to those of the samples without SP coupling are lower than the corresponding ratios of the square-root of photoluminescence decay rate due to the increases of their RC time constants (the product of device resistance and capacitance).

Phosphor-free, white-light LED under alternating-current operation.

A light-emitting diode structure, consisting of a p-GaN layer, a CdZnO/ZnO quantum-well (QW) structure, a high-temperature-grown ZnO layer, and a GaZnO layer, is fabricated. Under forward bias, the device effectively emits green-yellow light, from the QW structure, at the rim of device mesa. Under reverse bias, electrons in the valence band of the p-GaN layer move into the conduction band of the GaZnO layer, through a QW-state-assisted tunneling process, to recombine with the injected holes in the GaZnO layer, for emitting yellow-red and shallow ultraviolet light over the entire mesa area.

Dependencies of the emission behavior and quantum well structure of a regularly-patterned, InGaN/GaN quantum-well nanorod array on growth condition.

To achieve green emission from the sidewall non-polar quantum wells (QWs) of a GaN nanorod (NR) light-emitting diode, regularly patterned InGaN/GaN QW NR arrays are grown under various growth conditions of indium supply rate, QW growth temperature, and QW growth time for comparing their emission wavelength variations of the top-face c-plane and sidewall m-plane QWs based on photoluminescence and cathodoluminescence (CL) measurements. Although the variation trends of QW emission wavelength by changing those growth conditions in the NR structure are similar to those in the planar structure, the emission wavelength range of the QWs on an NR is significantly shorter than that in a planar structure under the same growth conditions. Under the growth conditions for a longer NR QW emission wavelength, the difference of emission wavelength between the top-face and sidewall QWs is smaller.

Enhancements of the emission and light extraction of a radiating dipole coupled with localized surface plasmon induced on a surface metal nanoparticle in a light-emitting device.

The radiated power enhancement and more congregated radiation of a radiating dipole within a GaN material when it is coupled with the localized surface plasmon (LSP) resonance modes induced on a surface Ag nanoparticle (NP) are numerically demonstrated. The numerical study is based on an algorithm including the induction of LSP resonance on the Ag NP by the source dipole and the feedback effect of the LSP resonance field on the source dipole behavior. The spectral peaks of radiated power enhancement correspond to the substrate LSP resonance modes with mode fields mainly distributed around the bottom of the Ag NP such that the coupling system radiates mainly into the GaN half-space.

Geometry and composition comparisons between c-plane disc-like and m-plane core-shell InGaN/GaN quantum wells in a nitride nanorod.

With the nano-imprint lithography and the pulsed growth mode of metalorganic chemical vapor deposition, a regularly-patterned, c-axis nitride nanorod (NR) array of quite uniform geometry with simultaneous depositions of top-face, c-plane disc-like and sidewall, m-plane core-shell InGaN/GaN quantum well (QW) structures is formed. The differences of geometry and composition between these two groups of QW are studied with scanning electron microscopy, cathodoluminescence, and transmission electron microscopy (TEM). In particular, the strain state analysis results in TEM observations provide us with the information about the QW width and composition.