Molecular beam epitaxy growth of a bilayer stacked InAs/GaAs quantum dot structure on a pure GaAs matrix has been systemically investigated.The influence of growth temperature and the InAs deposition of both layers on the optical properties and morphologies of the bilayer quantum dot（BQD） structures is discussed.By optimizing the growth parameters,InAs BQD emission at 1.436μm at room temperature with a narrower FWHM of 27 meV was demonstrated.The density of QDs in the second layer is around 9×10~9 to 1.4×10^（10） cm^（-2）. The BQD structure provides a useful way to extend the emission wavelength of GaAs-based material for quantum functional devices.
Molecular beam epitaxy growth of an In;Ga;As/GaAs quantum well（QW） structure（x equals to 0.17 or 0.3） on offcut（100） Ge substrate has been investigated.The samples were characterized by atomic force microscopy,photoluminescence（PL）,and high resolution transmission electron microscopy.High temperature annealing of the Ge substrate is necessary to grow GaAs buffer layer without anti-phase domains.During the subsequent growth of the GaAs buffer layer and an In;Ga;As/GaAs QW structure,temperature plays a key role. The mechanism by which temperature influences the material quality is discussed.High quality In;Ga;As/GaAs QW structure samples on Ge substrate with high PL intensity,narrow PL linewidth and flat surface morphology have been achieved by optimizing growth temperatures.Our results show promising device applications forⅢ-Ⅴcompound semiconductor materials grown on Ge substrates.
Molecular beam epitaxy growth of GaAs on an offcut Ge （100） substrate has been systemically investigated. A high quality GaAs/Ge interface and CaAs film on Ge have been achieved. High temperature annealing before GaAs deposition is found to be indispensable to avoid anti-phase domains. The quality of the GaAs film is found to strongly depend on the GaAs/Ge interface and the beginning of GaAs deposition. The reason why both high temperature annealing and GaAs growth temperature can affect epitaxial GaAs film quality is discussed. High quality InonTGao.s3As/GaAs strained quantum wells have also been achieved on a Ge substrate. Samples show flat surface morphology and narrow photoluminescence line width compared with the same structure sample grown on a GaAs substrate. These results indicate a large application potential for Ⅲ-Ⅴcompound semiconductor optoelectronic devices on Ge substrates.
The optimization of a SiO_2/TiO_2,SiO_2/ZnS double layer antireflection coating（ARC）on Ga_（0.5）In_（0.5）P/In_（0.02）Ga_（0.98）As/Ge solar cells for terrestrial application is discussed.The Al_（0.5）In_（0.5）P window layer thickness is also taken into consideration.It is shown that the optimal parameters of double layer ARC vary with the thickness of the window layer.
