Fabrication and optical studies of AlGaN/GaN quantum-well waveguides (original) (raw)
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Propagation properties of light in AlGaN/GaN quantum-well waveguides
Applied Physics Letters, 2001
The dynamic properties of light propagation in AlGaN/GaN-based multiple-quantum-well waveguides have been investigated by time-resolved photoluminescence ͑PL͒ spectroscopy. The waveguides were patterned with a fixed width of 0.5 m and length 500 m using electron-beam lithography and inductively coupled plasma dry etching. Our results reveal a remarkable decrease in the PL intensity as well as an increase in time delay of the temporal response as the location of the laser excitation spot on the waveguide is varied. These results can be understood in terms of polariton propagation in the waveguides. From the time delay of the temporal response, it has been determined that the speed of generated polaritons, with energy corresponding to the well transitions in the waveguides, is approximately (1.26Ϯ0.16)ϫ10 7 m/s. The implications of these results to waveguiding in optical devices based on the group III-nitride semiconductors are discussed.
Journal of Applied Physics, 2008
a-plane InGaN/GaN multiple quantum wells of different widths ranging from 3 to 12 nm grown on r-plane sapphire by metal-organic chemical vapor deposition were investigated. The peak emission intensity of the photoluminescence ͑PL͒ reveals a decreasing trend as the well width increases from 3 to 12 nm. Low temperature ͑9 K͒ time-resolved PL ͑TRPL͒ study shows that the sample with 3-nm-thick wells has the best optical property with a fastest exciton decay time of 0.57 ns. The results of cathodoluminescence and micro-PL scanning images for samples of different well widths further verify that the more uniform and stronger luminescence intensity distribution are observed for the samples of thinner quantum wells. In addition, more effective capturing of excitons due to larger localization energy E loc and shorter radiative lifetime of localized excitons are observed in thinner well width samples in the temperature dependent TRPL.
2016
The propagation properties of light in AIGaN/GaN multiple-quantum-well (MQW) waveguides have been studied by time-resolved photoluminescence (PL) spectroscopy. The waveguides were patterned with fixed width of 0.5 j.im but orientations varying from 3oo to 600 relative to the a-axis of GaN by electron-beam lithography and inductively-coupled plasma (ICP) dry etching. The peak position and line-width of the emission peak were found to vary systematically with orientations of the waveguides and followed the six-fold symmetry of the wurtzite structure. This is explained in terms of anisotropy of the exciton/carrier diffusion coefficient along the different crystal orientations of the semiconductor materials. We also observed a remarkable decrease in the PL intensity as well as increase in time delay of the temporal response as the location of the laser excitation spot on the waveguide is varied. These observations can be understood in terms ofexciton-polariton propagation in the wavegui...
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.
SPIE Proceedings, 2002
The propagation properties of light in AIGaN/GaN multiple-quantum-well (MQW) waveguides have been studied by timeresolved photoluminescence (PL) spectroscopy. The waveguides were patterned with fixed width of 0.5 j.im but orientations varying from 3oo to 600 relative to the a-axis of GaN by electron-beam lithography and inductively-coupled plasma (ICP) dry etching. The peak position and line-width of the emission peak were found to vary systematically with orientations of the waveguides and followed the six-fold symmetry of the wurtzite structure. This is explained in terms of anisotropy of the exciton/carrier diffusion coefficient along the different crystal orientations of the semiconductor materials. We also observed a remarkable decrease in the PL intensity as well as increase in time delay of the temporal response as the location of the laser excitation spot on the waveguide is varied. These observations can be understood in terms ofexciton-polariton propagation in the waveguides. The speed of generated polaritons with energy corresponding to the well transitions in the waveguides was determined from the time delay ofthe temporal response to be approximately (1.26 0.16) x iO rn/sec. The optical loss in the waveguides was determined to be about 5-8 cm' for different excitation intensities. The implications of these results to waveguiding in optical devices based on the 111-nitride semiconductors are discussed.
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.
AlGaN-GaN Quantum well optical properties
Intersubband transitions in Si-doped molecular beam epitaxy grown GaN/AlGaN multiple quantum wells on c-plane sapphire were investigated using the Fourier-transform infrared optical absorption technique. Several GaN quantum well samples were grown with either AlGaN bulk or GaN/AlGaN short period superlattice barriers. The measurements were made in a waveguide configuration utilizing a facet polished at 45°to the c plane. The integrated area of the intersubband transitions in several waveguides cut from different location of the wafer was measured, from which we estimated the two-dimensional electron gas density ͑͒. The measured values of are about two orders of magnitude larger than the Si doping level of ϳ8ϫ10 17 cm Ϫ3 , which is consistent with the polarization effects, particularly considering the large number of GaN/AlGaN interfaces. The internal quantum efficiency of the intersubband transitions was estimated to be on the order of 40% for samples with superlattice barriers.
Applied Physics Letters, 1997
Effects of well thickness and Si doping on the optical properties of GaN/AlGaN ͑MQWs͒ have been investigated by picosecond time-resolved photoluminescence ͑PL͒ measurements. Our results have yielded that ͑i͒ the optical transitions in nominally undoped MQWs with narrow well thicknesses (L w Ͻ40 Å) were blue shifted with respect to the GaN epilayer due to quantum confinement, however, no such blue shift was evident for the MQWs with well thicknesses larger than 40 Å, ͑ii͒ the band-to-impurity transitions were the dominant emission lines in nominally undoped MQWs of large well thicknesses (L w Ͼ40 Å) at low temperatures, and ͑iii͒ Si doping improved significantly the crystalline quality of MQWs of large well thicknesses (L w Ͼ40 Å). The implications of these results on the device applications based on III-nitride MQWs have been discussed.