Multi-section core-shell InGaN/GaN quantum-well nanorod light-emitting diode array (original) (raw)
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Quantum well engineering in InGaN/GaN core- shell nanorod structures
We report the ability to control relative InN incorporation in InGaN/GaN quantum wells (QWs) grown on the semi-polar and non-polar facets of a core-shell nanorod LED structure by varying the growth conditions. A study of the cathodoluminescence emitted from series of structures with different growth temperatures and pressures for the InGaN QW layer revealed that increasing the growth pressure had the effect of increasing InN incorporation on the semi-polar facets, while increasing the growth temperature improves the uniformity of light emission from the QWs on the non-polar facets.
Nano-structures and luminescence mechanisms of InGaN/GaN multiple quantum well light emitting diodes
The International Conference on Electrical Engineering, 2008
A series of InGaN/GaN MQW LEDs were prepared by low pressure metalorganic chemical vapor deposition (MOCVD) and studied on the nano-structural features correlated with optical properties, and luminescence emission mechanisms by analytical techniques of photoluminescence (PL), PL excitation (PLE), time resolved PL (TRPL), high-resolution (HR) X-ray diffraction (XRD) and HR transmission electron microscopy (TEM). They have shown the excellent optical and structural properties, evidenced by HRXRD, HRTEM and optical measurements. The quantum dot like structure features, unique T-behaviors of PL spectra, quantum confined Stokes effect, TRPL exploration with the variation of detecting energy and temperature and modeling analyses are studied and discussed.
Nanotechnology, 2011
For InGaN/GaN based nanorod devices using a top-down etching process, the optical output power is affected by non-radiative recombination due to sidewall defects (which decrease light output efficiency) and the mitigated quantum confined Stark effect (QCSE) due to strain relaxation (which increases internal quantum efficiency). Therefore, the exploration of low-temperature optical behaviors of nanorod light emitting diodes (LEDs) will help identify the correlation between these two factors. In this work, low-temperature electroluminescent (EL) spectra of InGaN/GaN nanorod arrays were explored and compared with those of planar LEDs. The nanorod LED exhibits a much higher optical output percentage increase when the temperature decreases. The increase is mainly attributed to the increased carriers in the quantum wells for radiative recombination. Also, due to a better spatial overlap of electrons and holes in the quantum wells, the increased number of carriers can be more efficiently recombined in the nanorod device. Next, while the nanorod array shows nearly constant peak energy in the EL spectra at various injection currents at the temperature of 300 K, a blue shift has been observed at 190 K. The results suggest that with less non-radiative recombination and thus more carriers in the quantum wells, carrier screening and band filling still prevail in the partially strain relaxed nanorods. Moreover, when the temperature drops to 77 K, the blue shift of both nanorod and planar devices disappears and the optical output power decreases since there are fewer carriers in the quantum wells for radiative recombination.
By means of time-resolved photoluminescence (PL) and confocal PL measurements, temporally and spatially resolved optical properties have been investigated on a number of In x Ga 1Àx N/GaN multiple-quantum-well (MQW) structures with a wide range of indium content alloys from 13% to 35% on ð11 22Þ semi-polar GaN with high crystal quality, obtained through overgrowth on nanorod templates. With increasing indium content, the radiative recombination lifetime initially increases as expected, but decreases if the indium content further increases to 35%, corresponding to emission in the green spectral region. The reduced radiative recombination lifetime leads to enhanced optical performance for the high indium content MQWs as a result of strong exciton localization, which is different from the behaviour of c-plane InGaN/GaN MQWs, where quantum confined Stark effect plays a dominating role in emission process. V
Optical Properties of GaN Nanorods Containing a Single or Multiple InGaN Quantum Wells
Japanese Journal of Applied Physics, 2013
Measurements of light emission from GaN nanorods of diameter between 80 and 350 nm, containing either a three-well multiple InGaN quantum well or a single quantum well, have been performed by photoluminescence (PL) and cathodoluminescence (CL) hyperspectral imaging. The PL underwent a Stark shift to the blue as the nanorod diameter was reduced, indicating substantial relaxation of the compressive strain in the quantum wells. The intensity of the nanorod emission per unit area can exceed that of the planar starting material. The CL measurements revealed that the wavelength of the quantum well emission varied with radial position in the nanorod. Simulations by a modal expansion method revealed that the light extraction efficiency varies with radial position and the variation is dependent on nanorod diameter. Finite difference time domain simulations showed that Bloch mode formation in the buffer layer below the nanorods impacts on the light extraction.
IEEE Journal of Quantum Electronics, 2000
A-plane In x Ga 1−x N / GaN ͑x = 0.09, 0.14, 0.24, and 0.3͒ multiple-quantum-wells ͑MQWs͒ samples, with a well width of about 4.5 nm, were achieved by utilizing r-plane sapphire substrates. Optical quality was investigated by means of photoluminescence ͑PL͒, cathodoluminescence, and time resolved PL measurements ͑TRPL͒. Two distinguishable emission peaks were examined from the low temperature PL spectra, where the high-and low-energy peaks were ascribed to quantum wells and localized states, respectively. Due to an increase in the localized energy states and absence of quantum confined Stark effect, the quantum efficiency was increased with increasing indium composition up to 24%. As the indium composition reached 30%, however, pronounced deterioration in luminescence efficiency was observed. The phenomenon could be attributed to the high defect densities in the MQWs resulted from the increased accumulation of strain between the InGaN well and GaN barrier. This argument was verified from the much shorter carrier lifetime at 15 K and smaller activation energy for In 0.3 Ga 0.7 N / GaN MQWs. In addition, the polarization-dependent PL revealed that the degree of polarization decreased with increasing indium compositions because of the enhancement of zero-dimensional nature of the localizing centers. Our detailed investigations indicate that the indium content in a-plane InGaN/GaN MQWs not only has an influence on optical performance, but is also important for further application of nitride semiconductors.
Thin Solid Films, 2006
InGaN/GaN multiple quantum well light emitting diode structures have been grown on sapphire substrates by metalorganic chemical vapor deposition. They are investigated, in this study, by high-resolution X-ray diffraction, high-resolution transmission electron microscopy, photoluminescence, and photoluminescence excitation. HR-XRD showed multiple satellite peaks up to 10th order due to the quantum well superlattice confinement effects. These indicate the high quality of layer interface structures of this sample. Excitation power-dependent photoluminescence shows that both piezoelectric field-induced quantum-confined Stark effect and band filling effect influence the luminescent properties of this sample. Temperature-dependent photoluminescence of this sample has also been studied. The peak position of the PL exhibits a monotonic red-shift and the full width at half maximum of the PL band shows a W-shaped temperature-dependent behavior with increasing temperature. From the photoluminescence excitation results, a large energy difference, so-called Stokes shift, between the band-edge absorption and emission was observed.
Photoluminescence of Single GaN/InGaN Nanorod Light Emitting Diode Fabricated on a Wafer Scale
Japanese Journal of Applied Physics, 2013
Time-resolved and time-integrated microphotoluminescence studies were performed on a single nanorod in an InGaN/GaN nanorod LED array fabricated on a wafer scale by nanoimprint lithography. Investigation into nano-LED emission properties and carrier dynamics are presented. Sharp peaks of 2 meV FWHM in the photoluminescence spectrum were observed at 4.2 K. Time resolved studies show a decrease in decay rate ∼ 50 ns after excitation in the nanorods, with a significantly longer lifetime than that seen in a plane single quantum well unprocessed LED wafer. The time evolution of the photoluminescence spectra implies that the slower decay rates are due to surface related localisation near the perimeter of the nanorods, resulting in a spatial separation of the recombining carriers at low excitation densities.
InGaN GaN Nanorod Light Emitting Arrays Fabricated by Silica Nanomasks
IEEE Journal of Quantum Electronics, 2008
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.