Characterization of InGaN structures grown by epitaxial lateral overgrowth over a-plane GaN template (original) (raw)
Related papers
Emission mechanisms of bulk GaN and InGaN quantum wells prepared by lateral epitaxial overgrowth
Applied Physics Letters, 1999
The emission mechanisms of bulk GaN and InGaN quantum wells ͑QWs͒ were studied by comparing their optical properties as a function of threading dislocation ͑TD͒ density, which was controlled by lateral epitaxial overgrowth. Slightly improved excitonic photoluminescence ͑PL͒ intensity was recognized by reducing TD density from 10 10 cm Ϫ2 to less than 10 6 cm Ϫ2 . However, the major PL decay time was independent of the TD density, but was rather sensitive to the interface quality or material purity. These results suggest that TDs simply reduce the net volume of light-emitting area. This effect is less pronounced in InGaN QWs where carriers are effectively localized at certain quantum disk size potential minima to form quantized excitons before being trapped in nonradiative pathways, resulting in a slow decay time. The absence of any change in the optical properties due to reduction of TD density suggested that the effective band gap fluctuation in InGaN QWs is not related to TDs.
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.
Luminescence in Highly Excited InGaN/GaN Multiple Quantum Wells Grown on GaN and Sapphire Substrates
Acta Physica Polonica A
We report on high-excitation luminescence spectroscopy in In x Ga 1−x N/GaN multiple quantum wells grown by MOCVD over sapphire and bulk GaN substrates. High excitation conditions enabled us to achieve a screening of the built-in field by free carriers. This allowed for the evaluation of the influence of band potential fluctuations due to the variation in In-content on efficiency of spontaneous and stimulated emission. InGaN/GaN multiple quantum wells grown on bulk GaN substrate exhibit a significantly lower stimulated emission threshold and thus enhanced lateral emission. Transient and dynamic properties of luminescence indicate a significant reduction in compositional disorder in homoepitaxially grown structures.
Journal of Crystal Growth, 2011
InGaN/GaN quantum wells (QWs) with symmetrical ultra thin (about 0.5nm) low temperature GaN (LT-GaN) layers bounding each InGaN layer were grown by metal-organic vapor phase epitaxy (MOVPE). From the high resolution X-ray diffraction (HR-XRD) measurement, it showed improved well-barrier interface abruptness compared to the reference MQWs without the LT-GaN layers. In addition, the V-defect density and surface roughness were reduced, especially with the depth of V-defect as low as 0.7nm. Based on the temperature dependence photoluminescence (TDPL) experiments, the internal quantum efficiency (IQE) was increased from 21.2% to 30.1% by inserting the LT-GaN layers. The carrier lifetime obtained from room temperature time resolved photoluminescence (TRPL) measurement was 7.95ns, which was longer than 5.34ns for reference MQWs. These results indicated that these additional symmetrical thin LT-GaN layers enhanced the mobility of indium and gallium atoms as well as suppressed the indium desorption for growth high quality InGaN layers and in turn improved its structural and luminescence properties.
Improved electroluminescence on nonpolarm -plane InGaN/GaN quantum wells LEDs
physica status solidi (RRL) – Rapid Research Letters, 2007
The remarkable progress in III-nitride semiconductors has enabled widespread development of high power and high efficiency optoelectronic devices. Due to its stability during epitaxial growth, the polar c-axis is the common orientation for the deposition of III-N film and heterostructures even though the performance of these devices suffers from strong polarization-related electric fields along the growth-direction. These polarization fields result in a separation between electron and hole wave functions as well as a reduction in radiative recombination rate in active regions . To avoid this situation, there have been several reports of light emitting diodes (LEDs) grown and fabricated on nonpolar aand m-plane gallium nitride (GaN) on r-plane sapphire and m-plane SiC substrates using metalorganic chemical vapor deposition (MOCVD) [5], hydride vapor phase epitaxy (HVPE) [6], or molecular beam epitaxy (MBE) . However, heteroepitaxy, which uses foreign substrates, causes a high density of extended defects [9] such as threading dislocations (TDs) and basal stacking faults (SFs). These defects can be sources of non-radiative recombination centers that reduce the internal quantum efficiency and additionally act as charge scattering centers that decrease the carrier mobil-
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.
Journal of Applied Physics, 2014
We have performed a detailed study of the impact of basal plane stacking faults (BSFs) on the optical properties of both a-plane InGaN/GaN quantum wells (QWs) and GaN template samples grown on r-sapphire. In particular we have used polarised photoluminescence excitation spectroscopy (P-PLE) to investigate the nature of the low temperature recombination as well as extracting information on the valence band (VB) polarisation anisotropy. Our low temperature P-PLE results revealed not only excitons associated with intersubband quantum well transitions and the GaN barrier material but also a transition associated with creation of excitons in BSFs. The strength of this BSF transition varied with detection energy across the quantum well emission suggesting that there is a significant contribution to the emission line width from changes in the local electronic environment of the QWs due to interactions with BSFs. Furthermore we observed a corresponding progressive increase in the VB splitting of the QWs as the detection energy was varied across the quantum well emission spectrum.
Luminescence efficiency of InGaN/GaN quantum wells on bulk GaN substrate
MRS Proceedings, 2005
Time-integrated and time-resolved photoluminescence measurements on InGaN quantum wells grown by MOCVD on two different substrates (sapphire and GaN) show that the luminescence efficiency in these structures strongly depends on the intensity of carrier excitation. While at low excitation densities the recombination of excited carriers is governed by localization effects the behavior drastically changes at higher densities. At room temperature a suppression of nonradiative recombination could be observed that leads to an super linear increase of the luminescence.
Structural, electrical, and optical characterizations of a-plane InGaN/GaN quantum well structures
2009
GaN and related ternary compounds have been widely used for fabrication of light emitting diodes (LEDs) and laser diodes (LDs). Especially, the low-dimensional systems such as quantum wells (QWs), quantum wires, and quantum dots have been investigated as an effective structure for improving the efficiency of light-emitting devices such as light emitting diodes and laser diodes. Generally, the quantum well active regions in I¿-nitride optoelectronic devices grown on conventional templates along the polar orientation have critical problems given by the quantum confined Stark effect (QCSE) due to the effects of strong piezoelectric and spontaneous polarizations. However, the QWs grown on nonpolar templates along aor m-directions are free from the QCSE since the polar-axis lies within the growth plane of the template. In this study, we achieved high quality a-plane GaN films on sapphire substrates and characterized structural, electrical and optical properties in the a-plane InGaN/GaN QW structures. High quality of a-plane GaN templates was confirmed by using selected area diffraction (SAD) patterns and high resolution x-ray diffraction (HRXRD) results. To investigate the electrical properties of aplane GaN QWs structures, the temperature-dependent carrier depth profiles which can determine the carrier confinement with nanoscale spatial resolution were studied. And the redshift of photoluminescence (PL) peaks with increasing temperature will be intensively discussed.
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