In this paper we reported our systematic studies on InSb interface growth in InAs/GaSb SLs structure. Two typical interfaces growth mode, migration-enhanced epitaxy (MEE) and conventional molecular beam epitaxy (MBE), were designed for the 12 ML InAs/12 ML GaSb SLs material and the detail properties were discussion by the experimental measurement and simulation analysis. Our results indicated that the surface of SLs sample with the InSb interface layers grown by MEE method shows smaller RMS both on the 2 μm x 2 μm and 50 μm x 50 μm scan area by AFM measurement, and its PL intensity is about 1.3 times stronger than that of SLs sample grown by MBE. Besides, the MEE samples had significant As composition in InSb interface layers which was extracted by the HRXRD fitting.
In the paper we report on a technology of removing the conducting GaSb substrate with the mechanical thinning and wet etch, and then the electrical measurement of non-intentionally doped long-wavelength Infrared (LWIR) type-II InAs/GaSb superlattices (SLs). The SL structures were made of periodic 15 InAs monolayers (MLs) and 7 GaSb MLs with cutoff wavelengths around 11 μm. A etch stop layer was grown between the GaSb substrate and SL for substrate removal for no chemical solution exists with enough selectivity between the GbSb and SLs during the wet etch process. After removing the GaSb substrate, the transport properties measurements of SLs are performed using temperature dependent from 20 k to 296 k and variable magnetic field Hall measurements. It is found that the LWIR SLs is n-type at the all temperatures. Meanwhile, from the result of the mobility spectrum analysis at 76 k, there are more than one type carrier conducting in the LWIR SLs material.
The direct replication of a periodic W/Si multilayer was investigated systematically. The W/Si multilayer was deposited by a high vacuum dc magnetron sputtering system. After deposition, the multilayer was transferred from the supersmooth mandrel onto a commercially available float glass substrate by the epoxy replication technique. The multilayer was characterized by the grazing incident x-ray reflectance (GIXR) measurement, atomic force microscope (AFM), and Zygo GPI interferometer before and after replication. The measured results showed that the multilayer structure and reflectivity were almost the same, and the surface roughness was 0.22 and 0.23 nm before and after replication, respectively. It was demonstrated that the W/Si multilayer was successfully replicated without modification of the structure, a significant increase of surface roughness, or apparent change of reflectivity. The optical figure of the substrate after replication experienced significant changes of many waves but was actually improved for this specific test. Future studies will focus on learning how to control the resulting optical figure of our replication process on a thin substrate.
We are developing a hard X-ray telescope utilizing multilayer supermirrors. This telescope is conical approximation of
the Wolter-I configuration with tightly nested shells. Because of the fact that different nested shell corresponds to
different grazing incident angle, so the optimum multilayer design depends on the grazing angle, and one would
therefore, ideally design a different coating for each of the nested mirror shells. However, as a matter of practicality, we
have to reduce the number of different designs for a reasonable compromise between the complexity of the calculation
and optimal performance.
In this paper, we investigate the effect of different angular classification on the effective area of the hard X-ray
telescope. Many groups of hard X-ray supermirrors are optimized with different grazing incident angles using a
numerical and analysis method. These supermirrors are divided into different number of groups, e.g. two, four, six, eight,
ten, twelve, fourteen, and sixteen, respectively, and the corresponding effective areas are calculated. Results show that
six groups of X-ray supermirrors are suitable for a reasonable compromise between optimal performance and the
complexity of the calculation and fabrication.
A numerical and analysis method for optimizing multilayer supermirrors is developed based on the combination of the
power-law method and the local optimization method of simplex algorithm. The parameters in the power-law formula are
optimized by genetic algorithm. This allows a global minimization of the merit function and a many-fold decrease of the
computing time. Several groups of X-ray supermirrors with the energy extended to 30 keV are successfully designed
using this optimization method for a hard X-ray telescope. Tungsten and boron carbide are chosen as the multilayer
materials. High reflectivity and high effective area are obtained, indicating that this numerical and analysis method is an
effective tool to design hard X-ray supermirrors.