Detailed studies with spectral and time-resolved photoluminescence, photoluminescence excitation, and absorption spectroscopies show the formation of type-II quantum structures ͑quantum dots͒ in a Zn-Se-Te multilayer system with submonolayer quantities of Te. Moreover, it is shown that in addition to these quantum dots, Te isoelectronic centers are also present in the same material system and contribute to the photoluminescence emissions. This could be siginificant for the better understanding of the scaling laws between many-atom systems ͑e.g., quantum dots͒ and few-atom systems ͑e.g., isoelectronic centers͒.
Using surface enhanced Raman spectroscopy (SERS), we observed Raman enhancements (104−105) for pyridine molecules adsorbed on II−VI semiconductor quantum dots on (uncapped CdSe/ZnBeSe) produced by molecular beam epitaxy. When a monolayer of pyridine is adsorbed on these structures, excitation at 488 nm produces intense Raman spectra, a very large enhancement of the a1, b1, and b2 modes. This indicates the presence of charge transfer as a contributor to the enhancement. Furthermore, the excitation wavelength is in the vicinity of several interband transitions located both in the quantum dots and the wetting layer, and it is likely that these resonances also contribute to the enhancement factor.
We report on a backilluminated GaN/Al0.18Ga0.82N heterojunction ultraviolet (UV) photodetector with high internal gain based on metal-semiconductor-metal structures. A narrow band pass spectral response between 365 and 343 nm was achieved. When operating in dc mode, the responsivity reaches up to the order of 102 A/W under weak UV illumination, which is due to enormous internal gain up to 103. The linear dependence of photocurrent on bias and its square root dependence on optical power are found and explained by a trapping and recombination model. The high photocurrent gain is attributed to trapping and recombination centers with an acceptor character induced by dislocations in GaN.
The interband transitions of a single quantum well structure of Zn0.53Cd0.47Se/Zn0.27Cd0.23Mg0.50Se (lattice matched to InP) were evaluated using contactless electroreflectance at room temperature. From a comparison of the measured optical transitions with those calculated using the envelope function approximation we determined that the conduction band offset for this system is given by the parameter Qc=ΔEc/ΔE0=0.82±0.02, which yields ΔEc of 590 meV. Such a large conduction band offset may be useful for the design of quantum cascade lasers and other devices based on intersubband transitions.
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