Type II superlattices (SLs) short period InAs(4ML)/GaSb(8ML) were grown by molecular-beam epitaxy on lattice-mismatched GaAs substrates and on GaSb substrates. A smooth GaSb epilayer was formed on GaAs substrates by inserting mulit-buffer layers including an interfacial misfit mode AlSb quantum dot layer and AlSb/GaSb superlattices smooth layer. SLs grown on GaAs substrates (GaAs-based SLs) showed well-resolved satellite peaks in XRD. GaSb-based SLs with better structural quality and smoother surface showed strong photoluminescence at 2.55 μm with a full width at half maximum (FWHM) of 20 meV, narrower than 31 meV of GaAs-based SLs. Inferior optical absorption of GaAs-based SL was observed in the range of 2―3 μm. Photoresponse of GaSb-based SLs showed the cut-off wavelength at 2.6 μm.
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.
We develop a modified two-step method of growing high-density and narrow size-distribution InAs/GaAs quantum dots （QDs） by molecular beam epitaxy. In the first step, high-density small InAs QDs are formed by optimizing the continuous deposition amount. In the second step, deposition is carried out with a long growth interruption for every 0.1 InAs monolayer. Atomic force microscope images show that the high-density （～5.9 × 10^11 cm^-2） good size-uniformity InAs QDs are achieved. The strong intensity and narrow linewidth （27.7 meV） of the photoluminescence spectrum show that the QDs grown in this two-step method have a good optical quality.
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.
