We present a study on InAs/InGaAs QDs nanostructures grown by molecular beam epitaxy on InGaAs metamorphic buffers, that are designed so as to determine the strain of QD and, then, to shift the luminescence emission t...We present a study on InAs/InGaAs QDs nanostructures grown by molecular beam epitaxy on InGaAs metamorphic buffers, that are designed so as to determine the strain of QD and, then, to shift the luminescence emission towards the 1.5 μm region （QD strain engineering）. Moreover, we embed the QDs in InAIAs or GaAs barriers in addition to the InGaAs confining layers, in order to increase the activation energy for confined carrier thermal escape; thus, we reduce the thermal quenching of the photoluminescence, which prevents room temperature emission in the long wavelength range. We study the dependence of QD properties, such as emission energy and activation energy, on barrier thickness and height and we discuss how it is possible to compensate for the barrier-induced QD emission blue-shift taking advantage of QD strain engineering. Furthermore, the combination of enhanced barriers and QD strain engineering in such metamorphic QD nanostmctures allowed us to obtain room temperature emission up to 1.46μm, thus proving how this is a valuable approach in the auest for 1.55 um room temperature emission from ODs grown on GaAs substrates.展开更多
Resistivity and Hall effect measurements on n-type undoped Ga-rich InxGa1-xN （0.06 ≤ x ≤ 0.135） alloys grown by metal-organic vapour phase epitaxy （MOVPE） technique are carried out as a function of temperature ...Resistivity and Hall effect measurements on n-type undoped Ga-rich InxGa1-xN （0.06 ≤ x ≤ 0.135） alloys grown by metal-organic vapour phase epitaxy （MOVPE） technique are carried out as a function of temperature （15-350 K）. Within the experimental error, the electron concentration in Inx Ga1-x N alloys is independent of temperature while the resistivity decreases as the temperature increases. Therefore, Inx Ga1-xN （0.06 ≤ x ≤0.135） alloys are considered in the metallic phase near the Mort transition. It has been shown that the temperaturedependent metallic conductivity can be well explained by the Mort model that takes into account electron-electron interactions and weak localization effects.展开更多
Taking the full advantage of the conformal growth characterizing atomic layer deposition(ALD),the possibility to grow Co thin films,with thickness from several tens down to few nanometers on top of a granular topologi...Taking the full advantage of the conformal growth characterizing atomic layer deposition(ALD),the possibility to grow Co thin films,with thickness from several tens down to few nanometers on top of a granular topological insulator(TI)Sb2Tes film,exhibiting a quite high surface roughness(2-5 nm),was demonstrated.To study the Co growth on the Sb2Tes substrate,we performed simultaneous Co depositions also on sputtered Pt substrates for comparison.We conducted a thorough chemical-structural characterization of the Co/Sb2Tes and Co/Pt heterostructures,confirming for both cases,not only an excellent conformality,but also the structural continuity of the Co layers.X-ray diffraction(XRD)and high-resolution transmission electron microscope(HRTEM)analyses evidenced that Co on Sb2Te3 grows preferentially oriented along the[0oe]direction,following the underlying rhombohedric substrate.Differently,Co crystallizes in a cubic phase oriented along the[111]direction when deposited on Pt.This work shows that,in case of deposition of crystalline materials,the ALD surface selectivity and conformality can be extended to the definition of local epitaxy,where in-plane ordering of the crystal structure and mosaicity of the developed crystallized grains are dictated by the underlying substrate.Moreover,a highly sharp and chemically-pure Co/Sb2Tes interface was evidenced,which is promising for the application of this growth process for spintronics.展开更多
The room-temperature light emission of uncapped III-V semiconductor quantum dots is used to investigate the properties and evolution of the surface under exposure to a humid environment. Enhanced photoluminescence int...The room-temperature light emission of uncapped III-V semiconductor quantum dots is used to investigate the properties and evolution of the surface under exposure to a humid environment. Enhanced photoluminescence intensity resulting from exposure to polar molecules has already been reported; here we demonstrate that the external environment also has a relevant effect on the emission energy of quantum dots. Experimental results are interpreted on the basis of a model of the quantum system that takes into account the formation of oxide on pristine III-V surfaces and the presence of surface states. As a result of our study, we can clearly distinguish the effect of surface oxidation from that of surface state passivation on the emission of InAs surface quantum dots. This work sheds new light on the properties of semiconductor surface quantum dots as building blocks of novel and highly efficient sensing devices based on optical transduction.展开更多
基金The work has been partially supported by the "SANDiE" Networkof Excellence of EU(contract no. NMP4-CT-2004-500101).
文摘We present a study on InAs/InGaAs QDs nanostructures grown by molecular beam epitaxy on InGaAs metamorphic buffers, that are designed so as to determine the strain of QD and, then, to shift the luminescence emission towards the 1.5 μm region （QD strain engineering）. Moreover, we embed the QDs in InAIAs or GaAs barriers in addition to the InGaAs confining layers, in order to increase the activation energy for confined carrier thermal escape; thus, we reduce the thermal quenching of the photoluminescence, which prevents room temperature emission in the long wavelength range. We study the dependence of QD properties, such as emission energy and activation energy, on barrier thickness and height and we discuss how it is possible to compensate for the barrier-induced QD emission blue-shift taking advantage of QD strain engineering. Furthermore, the combination of enhanced barriers and QD strain engineering in such metamorphic QD nanostmctures allowed us to obtain room temperature emission up to 1.46μm, thus proving how this is a valuable approach in the auest for 1.55 um room temperature emission from ODs grown on GaAs substrates.
文摘Resistivity and Hall effect measurements on n-type undoped Ga-rich InxGa1-xN （0.06 ≤ x ≤ 0.135） alloys grown by metal-organic vapour phase epitaxy （MOVPE） technique are carried out as a function of temperature （15-350 K）. Within the experimental error, the electron concentration in Inx Ga1-x N alloys is independent of temperature while the resistivity decreases as the temperature increases. Therefore, Inx Ga1-xN （0.06 ≤ x ≤0.135） alloys are considered in the metallic phase near the Mort transition. It has been shown that the temperaturedependent metallic conductivity can be well explained by the Mort model that takes into account electron-electron interactions and weak localization effects.
基金We acknowledge the MP1402-Hooking together the European research in atomic layer deposition(HERALD)COST action and the Horizon 2020 project SKYTOP"Skyrmion-Topological Insulator and Weyl Semimetal Technology"(FETPROACT-2018-01,n.824123)Efforts at Wayne State University were supported by the U.S.National Science Foundation(Grant No.CHE-1607973)and EMD Performance Materials.
文摘Taking the full advantage of the conformal growth characterizing atomic layer deposition(ALD),the possibility to grow Co thin films,with thickness from several tens down to few nanometers on top of a granular topological insulator(TI)Sb2Tes film,exhibiting a quite high surface roughness(2-5 nm),was demonstrated.To study the Co growth on the Sb2Tes substrate,we performed simultaneous Co depositions also on sputtered Pt substrates for comparison.We conducted a thorough chemical-structural characterization of the Co/Sb2Tes and Co/Pt heterostructures,confirming for both cases,not only an excellent conformality,but also the structural continuity of the Co layers.X-ray diffraction(XRD)and high-resolution transmission electron microscope(HRTEM)analyses evidenced that Co on Sb2Te3 grows preferentially oriented along the[0oe]direction,following the underlying rhombohedric substrate.Differently,Co crystallizes in a cubic phase oriented along the[111]direction when deposited on Pt.This work shows that,in case of deposition of crystalline materials,the ALD surface selectivity and conformality can be extended to the definition of local epitaxy,where in-plane ordering of the crystal structure and mosaicity of the developed crystallized grains are dictated by the underlying substrate.Moreover,a highly sharp and chemically-pure Co/Sb2Tes interface was evidenced,which is promising for the application of this growth process for spintronics.
文摘The room-temperature light emission of uncapped III-V semiconductor quantum dots is used to investigate the properties and evolution of the surface under exposure to a humid environment. Enhanced photoluminescence intensity resulting from exposure to polar molecules has already been reported; here we demonstrate that the external environment also has a relevant effect on the emission energy of quantum dots. Experimental results are interpreted on the basis of a model of the quantum system that takes into account the formation of oxide on pristine III-V surfaces and the presence of surface states. As a result of our study, we can clearly distinguish the effect of surface oxidation from that of surface state passivation on the emission of InAs surface quantum dots. This work sheds new light on the properties of semiconductor surface quantum dots as building blocks of novel and highly efficient sensing devices based on optical transduction.
