Nanorod Light Emitting Diode Arrays Research Articles

The effects of nanocavity and photonic crystal in InGaN/GaN nanorod LED arrays.

InGaN/GaN nanorod light-emitting diode (LED) arrays were fabricated using nanoimprint and reactive ion etching. The diameters of the nanorods range from 120 to 300 nm. The integral photoluminescence (PL) intensity for 120 nm nanorod LED array is enhanced as 13 times compared to that of the planar one. In angular-resolved PL (ARPL) measurements, there are some strong lobes as resonant regime appeared in the far-field radiation patterns of small size nanorod array, in which the PL spectra are sharp and intense. The PL lifetime for resonant regime is 0.088 ns, which is 40 % lower than that of non-resonant regime for 120 nm nanorod LED array. At last, three dimension finite difference time domain (FDTD) simulation is performed. The effects of guided modes coupling in nanocavity and extraction by photonic crystals are explored.

Regularly patterned non-polar InGaN/GaN quantum-well nanorod light-emitting diode array.

The growth and process of a regularly patterned nanorod (NR)- light-emitting diode (LED) array with its emission from sidewall non-polar quantum wells (QWs) are demonstrated. A pyramidal un-doped GaN structure is intentionally formed at the NR top for minimizing the current flow through this portion of the NR such that the injection current can be effectively guided to the sidewall m-plane InGaN/GaN QWs for emission excitation by a conformal transparent conductor (GaZnO). The injected current density at a given applied voltage of the NR LED device is similar to that of a planar c-plane or m-plane LED. The blue-shift trend of NR LED output spectrum with increasing injection current is caused by the non-uniform distributions of QW width and indium content along the height on a sidewall. The photoluminescence spectral shift under reversed bias confirms that the emission of the fabricated NR LED comes from non-polar QWs.

Light-emitting device with regularly patterned growth of an InGaN/GaN quantum-well nanorod light-emitting diode array

A light-emitting device consisting of a two-dimensional regularly patterned InGaN/GaN quantum well (QW) nanorod (NR) light-emitting diode (LED) array is implemented and characterized. The NR p-i-n structure includes n-GaN NR core and essentially conformal p-GaN shell. The active regions include nonpolar sidewall QWs and polar top-face QWs. A conformal layer of transparent GaZnO of low resistivity is deposited onto the NR LED structure for spreading the injection current over the sidewalls. It is found that the blue-shift range of the output spectral peak in increasing injection current is smaller than that of a planar LED of about the same operation wavelength in a similar variation range of injection current density although it is nonzero. The small blue-shift range is attributed to the mixed emission contributions from the nonpolar sidewall QWs and polar top-face QWs.

Investigation of the strain induced optical transition energy shift of the GaN nanorod light emitting diode arrays

Strain in the semiconductor light emitting layers has profound effect on the energy band structure and the optical properties of the light emitting diodes (LEDs). Here, we report the fabrication and characterization of GaN nanorod LED arrays. We found that the choice of nanorod passivation materials results in the variation of strain in the InGaN/GaN quantum wells, and thus the corresponding change of light emission properties. The results were further investigated by performing Raman measurement to understand the strain of nanorods with different passivation materials and by calculating the optical transition energy of the devices under the influence of strain-induced deformation potential and the piezoelectric polarization field.

GaN based nanorod light emitting diodes by selective area epitaxy

AbstractSite‐controlled, vertically aligned gallium nitride nanorod light emitting diode (LEDs) arrays with high aspect ratio have been synthesized via catalyst‐free metalorganic chemical vapor deposition. Nanorod LEDs arrays with ∼1 μm in length and ∼200 nm in diameter were prepared on n‐type gallium nitride film on sapphire substrates using nanoporous silicon dioxide as a growth mask patterned by anodized aluminum oxide. GaN nanorod LEDs demonstrate a higher photoluminescence in intensity, compared to that of a planar GaN. This is contributed to the improvement of light extraction due to the faceted nanostructures and the improvement in crystal quality. In addition, more Indium incorporation has been demonstrated compared to the control LEDs structure. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High performance InGaN/GaN nanorod light emitting diode arrays fabricated by nanosphere lithography and chemical mechanical polishing processes

We fabricated InGaN/GaN nanorod light emitting diode (LED) arrays using nanosphere lithography for nanorod formation, PECVD (plasma enhanced chemical vapor deposition) grown SiO(2) layer for sidewall passivation, and chemical mechanical polishing for uniform nanorod contact. The nano-device demonstrates a reverse current 4.77nA at -5V, an ideality factor 7.35, and an optical output intensity 6807mW/cm(2) at the injection current density 32A/cm(2) (20mA). Moreover, the investigation of the droop effect for such a nanorod LED array reveals that junction heating is responsible for the sharp decrease at the low current.

Fabrication and Characterizations of Nanorod Light Emitting Diode Arrays Using Nanosphere Lithography

In this paper, by sping-coating a mono layer of nanospheres (nanoparticles) on top of the sample, the technology of nanosphere lithography is developed and applied to GaN based LED epi-structures. By etching the p-type GaN further through the active region, p-i-n nanorods are exposed all over the mesa area. By inserting a spacer layer in between rods, nanrod LED arrays can be realized without shorting the p-type contact to n-GaN. The electrical and optical properties of the InGaN/GaN-based nano-devices are investigated at room temperatures.

High output power density from GaN-based two-dimensional nanorod light-emitting diode arrays

Here we propose and realize a scheme for making a direct contact to a two-dimensional nanorod light-emitting diode (LED) array using the oblique-angle deposition approach. And, more importantly, we demonstrate highly efficient electrical carrier injection into the nanorods. As a result, we show that at a 20 mA dc current injection, the light output power density of our nanorod LED array is 3700 mW cm−2. More general, this contact scheme will pave the ways for making direct contacts to other kinds of nanoscale optoelectronic devices.

Strain Relaxed GaN/InGaN Nanorod Light Emitting Arrays

We present a practical top-down etch process to fabricate InGaN/GaN multiple quantum well nanorod structure. By using nature lithography to define nanostructure, and a space layer to prevent p-type contact from connecting n-type GaN, the nanorod light emitting diode array is realized. The quantum confine stark effect is suppressed in nanorod LEDs which is indicated by their nearly constant electroluminescence peak wavelength at the injection current range between 25mA and 100mA. Furthermore, Raman measurement confirms strain relaxation between lattice mismatch layers of such a nanostructure.

GaN nanorod light emitting diode arrays with a nearly constant electroluminescent peak wavelength

A practical process to fabricate InGaN/GaN multiple quantum well light emitting diodes (LEDs) with a self-organized nanorod structure is demonstrated. The nanorod array is realized by using nature lithography of surface patterned silica spheres followed by dry etching. A layer of spin-on-glass (SOG), which intervening the rod spacing, serves the purpose of electric isolation to each of the parallel nanorod LED units. The electroluminescence peak wavelengths of the nanorod LEDs nearly remain as constant for an injection current level between 25mA and 100mA, which indicates that the quantum confined stark effect is suppressed in the nanorod devices. Furthermore, from the Raman light scattering analysis we identify a strain relaxation mechanism for lattice mismatch layers in the nanostructure.

InGaN–GaN Nanorod Light Emitting Arrays Fabricated by Silica Nanomasks

We present a practical process to fabricate InGaN-GaN multiple quantum well nanorod structures. By using silica nanoparticles as the etch mask and followed by dry etching, nanorods with diameter 100 nm can be uniformly fabricated over the entire 2-in wafer. The photoluminescence spectra of the InGaN-GaN p-i-n nanorod structure are extracted at room and low temperatures. Also, discrete density of states can be observed at the temperature below 60 K. We further fabricate nanorod light emitting devices using a planarization approach to deposit p-type electrode on the tips of nanorods. Current-voltage curves and electroluminescent results of nanorod light emitting diode arrays are demonstrated.