InGaN/GaN quantum wells

FlG. 13.8. Schematic and optical properties of the hybrid quantum-well/nanocrystal structure, (a). The structure consists of an InGaN/GaN quantum-well heterostructure with a monolayer of TOPO/TOP-capped CdSe/ZnS core/shell nanocrystals on top of it. Electron-hole pairs in the quantum well can experience nonradiative resonant transfer into nanocrystals. The nanocrystals excited by energy transfer produce emission with a wavelength determined by the nanocrystal size. (b). The emission of the quantum well (blue) spectrally overlaps with the absorption of the nanocrystals (green). For CdSe nanocrystals with 1.9 nm radius, the emission wavelength is around 575 nm (red) (from (13)). 

InGaN/GaN QUANTUM WELLS FABRICATION, OPTICAL PROPERTIES AND APPLICATION IN LIGHT EMITTING DEVICES... 

InGaN/GaN QUANTUM WELL HETEROSTRUCTURES GROWN ON SILICON FOR UV-BLUE LASERS AND LIGHT EMITTING DIODES... 

Semipolar InGaN/GaN Quantum Wells for Highly Functional Light Emitters... 

Effect of plasma-induced damage on electrical properties of InGaN/GaN multiple quantum well light-emitting diodes... 

Carrier and exciton dynamics in InGaN/GaN MQWs have also been studied at a high optical pumping power [34], At 7 K, a radiative decay lifetime of 250 ps was observed for the dominant transition at a generated carrier density of 1012/cm2. The time-resolved measurement showed that the decay of PL has a bimolecular recombination characteristic. At room temperature, the carrier recombination was found to be dominated by non-radiative processes with a measured lifetime of 130 ps. Well width dependence of carrier and exciton dynamics in InGaN/GaN MQWs has also been measured [35]. The dominant radiative recombination at room temperature was attributed to the band-to-band transition. Combined with an absolute internal quantum efficiency measurement, a lower limit of 4 x 10 9 cm3/s on the bimolecular radiative recombination coefficient B was obtained. At low temperatures, the carrier... 

A phenomenon which is related to the PPC effects is the optical metastability in GaN. Optical metastability has been observed in GaN epilayers and InGaN/GaN multiple quantum wells [24-26]. Optical metastability in bulk GaN was manifested by a photoinduced decrease in the output intensity of the bandedge transition at 365 nm followed by an increase in the output intensity of a new emission band at 378 nm [25], The recovery time associated with the observed optical metastability is very long (weeks). The cause for such an effect was attributed to the presence of traps in bulk GaN [25], In... 

InGaN/GaN multiple quantum well laser heterostructures... 

Laser action without any visible degradation was obtained in the InGaN/GaN MQW heterostmctures up to T = 585 K. The laser spectra at low / xc consist of one very narrow line with the lowest FWHM of 0.04 nm. All lasers had well pronounced threshold input-output characteristics. The external differential quantum efficiency of the laser operating at 452 nm for TE polarisation amounts to the value of 77 = 3%. The maximum total energy and power per pulse from both facets were 300 nJ and 40 W, correspondingly, at room temperature for lias = 452 nm. 

Peculiarities of temperature and excitation intensity dependencies of radiative recombination of InGaN/GaN multiple quantum well (MQW) heterostructures grown on silicon were analysed to determine the participation of carriers localized in In-rich nanosized clusters in spontaneous emission, gain and lasing. X-ray diffraction measurements were carried out to characterize the structure of MQWs. 

In order to improve the emission efficiency of these devices, quantum well structures are introduced for efficient trapping of electron and hole pairs. A quantum well is a multilayered structure where a semiconductor material with a low bandgap (well) is sandwiched between two layers of semiconductor materials with higher bandgap (barriers). A typical InGaN/GaN multiple quantum well structure in a blue InGaN based LED is shown in Figure 9. 

---