An organic quantum well based on high-quality crystalline heteroepitaxy films

A meaningful organic quantum well based on crystalline heteroepitaxy films is constructed. The quantum confinement effect is demonstrated by its reflections on optics and electrics: the blueshift of the optical characteristic peaks and the negative differential resistance at room temperature. The realization of an organic quantum well indicates the highly delocalized transport mechanism in well-defined organic crystalline systems and promises novel organic "quantum" optoelectronic devices.

Time-resolved photoluminescence studies of annealed 1.3-μm GaInNAsSb quantum wells

Time-resolved photoluminescence (PL) was applied to study the dynamics of carrier recombination in GaInNAsSb quantum wells (QWs) emitting near 1.3 μm and annealed at various temperatures. It was observed that the annealing temperature has a strong influence on the PL decay time, and hence, it influences the optical quality of GaInNAsSb QWs. At low temperatures, the PL decay time exhibits energy dependence (i.e., the decay times change for different energies of emitted photons), which can be explained by the presence of localized states. This energy dependence of PL decay times was fitted by a phenomenological formula, and the average value of E0, which describes the energy distribution of localized states, was extracted from this fit and found to be smallest (E0 = 6 meV) for the QW annealed at 700°C. In addition, the value of PL decay time at the peak energy was compared for all samples. The longest PL decay time (600 ps) was observed for the sample annealed at 700°C. It means that based on the PL dynamics, the optimal annealing temperature for this QW is approximately 700°C.

Uniform SiGe/Si quantum well nanorod and nanodot arrays fabricated using nanosphere lithography

This study fabricates the optically active uniform SiGe/Si multiple quantum well (MQW) nanorod and nanodot arrays from the Si0.4Ge0.6/Si MQWs using nanosphere lithography (NSL) combined with the reactive ion etching (RIE) process. Compared to the as-grown sample, we observe an obvious blueshift in photoluminescence (PL) spectra for the SiGe/Si MQW nanorod and nanodot arrays, which can be attributed to the transition of PL emission from the upper multiple quantum dot-like SiGe layers to the lower MQWs. A possible mechanism associated with carrier localization is also proposed for the PL enhancement. In addition, the SiGe/Si MQW nanorod arrays are shown to exhibit excellent antireflective characteristics over a wide wavelength range. These results indicate that SiGe/Si MQW nanorod arrays fabricated using NSL combined with RIE would be potentially useful as an optoelectronic material operating in the telecommunication range.

Intersubband absorption properties of high Al content AlxGa1-xN/GaN multiple quantum wells grown with different interlayers by metal organic chemical vapor deposition

High Al content AlxGa1-xN/GaN multiple quantum well (MQW) films with different interlayers were grown by metal organic chemical vapor deposition. These MQWs were designed to achieve intersubband (ISB) absorption in the mid-infrared spectral range. We have considered two growth conditions, with AlGaN interlayer and GaN/AlN superlattice (SL) interlayer, both deposited on GaN-on-sapphire templates. Atomic force microscopy images show a relatively rough surface with atomic-step terraces and surface depression, mainly dominated by dislocations. High-resolution X-ray diffraction and transmission electron microscopy analyses indicate that good crystalline quality of the AlGaN/GaN MQW layer could be achieved when the AlGaN interlayer is inserted. The ISB absorption with a peak at 3.7 μm was demonstrated in MQW films with AlGaN interlayer. However, we have not observed the infrared absorption in MQW films with GaN/AlN SL interlayer. It is believed that the high dislocation density and weaker polarization that resulted from the rough interface are determinant factors of vanished ISB absorption for MQW films with the GaN/AlN SL interlayer.

Exciton properties in zincblende InGaN-GaN quantum wells under the effects of intense laser fields

: In this work, we study the exciton states in a zincblende InGaN/GaN quantum well using a variational technique. The system is considered under the action of intense laser fields with the incorporation of a direct current electric field as an additional external probe. The effects of these external influences as well as of the changes in the geometry of the heterostructure on the exciton binding energy are discussed in detail.