The optical properties of bulk InAs0.936Bi0.064 grown by molecular beam epitaxy on a (100)-oriented GaSb substrate are measured using spectroscopic ellipsometry. The index of refraction and absorption coefficient are measured over photon energies ranging from 44 meV to 4.4 eV and are used to identify the room temperature bandgap energy of bulk InAs0.936Bi0.064 as 60.6 meV. The bandgap of InAsBi is expressed as a function of Bi mole fraction using the band anticrossing model and a characteristic coupling strength of 1.529 eV between the Bi impurity state and the InAs valence band. These results are programmed into a software tool that calculates the miniband structure of semiconductor superlattices and identifies optimal designs in terms of maximizing the electron-hole wavefunction overlap as a function of transition energy. These functionalities are demonstrated by mapping the design spaces of lattice-matched GaSb/InAs0.911Sb0.089 and GaSb/InAs0.932Bi0.068 and strain-balanced InAs/InAsSb, InAs/GaInSb, and InAs/InAsBi superlattices on GaSb. The absorption properties of each of these material systems are directly compared by relating the wavefunction overlap square to the absorption coefficient of each optimized design. Optimal design criteria are provided for key detector wavelengths for each superlattice system. The optimal design mid-wave infrared InAs/InAsSb superlattice is grown using molecular beam epitaxy, and its optical properties are evaluated using spectroscopic ellipsometry and photoluminescence spectroscopy.

The physical and chemical properties of 210 nm thick InAsSbBi layers grown by molecular beam epitaxy at temperatures between 400 and 430 °C on (100) GaSb substrates are investigated using Rutherford backscattering, X-ray diffraction, transmission electron microscopy, Nomarski optical microscopy, and atomic force microscopy. The results indicate that the layers are nearly lattice matched, coherently strained, and contain dilute Bi mole fractions. Large surface droplets with diameters on the order of 1 μm and densities on the order of 106 cm−2 are observed when the InAsSbBi growth is performed with lean As overpressures around 1%. Surface droplets are not observed when the As overpressure is increased to 4%. Small crystalline droplets with diameters on the order of 70 nm and densities on the order of 1010 cm−2 are observed between the large droplets for InAsSbBi grown at 430 °C. Analysis of one of the small droplets indicates a misoriented zinc blende crystal structure composed primarily of In, Sb, and Bi, with a lattice constant of 6.543 ± 0.038 Å. Lateral modulation in the Bi mole fraction is observed in InAsSbBi layers grown at 400 °C.

Several 1 μm thick, nearly lattice-matched InAsBi layers grown on GaSb are examined using Rutherford backscattering spectrometry and X-ray diffraction. Random Rutherford backscattering measurements indicate that the average Bi mole fraction ranges from 0.0503 to 0.0645 for the sample set, and ion-channeling measurements indicate that the Bi atoms are substitutional. The X-ray diffraction measurements show a diffraction sideband near the main (004) diffraction peak, indicating that the Bi mole fraction is not laterally uniform in the layer. The average out-of-plane tetragonal distortion is determined by modeling the main and sideband diffraction peaks, from which the average unstrained lattice constant of each sample is determined. By comparing the Bi mole fraction measured by random Rutherford backscattering with the InAsBi lattice constant for the sample set, the lattice constant of zinc blende InBi is determined to be 6.6107 Å.

The structural and optical properties of pseudomorphic InAsSbBi grown on GaSb are examined using reflection high-energy electron diffraction, X-ray diffraction, Rutherford backscattering spectrometry, and spectroscopic ellipsometry. The layer studied is 210 nm thick and was grown by molecular beam epitaxy at 280 °C under a (2 × 3) surface reconstruction using near-stoichiometric fluxes. The material is homogeneous and single crystal with no observable defects or surface Bi droplets. The group-V mole fractions are determined using Rutherford backscattering measurements of the Bi mole fraction and X-ray diffraction measurements of the lattice tetragonal distortion. The bandgap energy is determined from the room temperature optical constants measured using spectroscopic ellipsometry. These and measurements from pseudomorphic InAsSb and InAsBi on GaSb are utilized to describe the bandgap energy of InAsSbBi as a function of mole fraction using a bandgap bowing model.

Efficient infrared detection and emission is desired for numerous applications, including navigation, night vision, communications, imaging, spectroscopy, and launch detection. Incorporation of bismuth in InAs alloys results in larger bandgap reduction per unit strain than antimony and provides an efficient means of tuning the bandgap while limiting the level of biaxial strain that can introduce defects that reduce optical quality [1]. Pseudomorphic InAsSbBi grown on GaSb is of interest because it permits the designer to independently adjust bandgap and strain by varying the group-V mole fractions as well as providing improved hole confinement over InAsSb alone. This study describes the TEM characterization of 210 nm thick, pseudomorphic InAsSbBi layers grown under various V/III flux ratios and temperatures ranging from 280°C to 430ºC. The changes in microstructure that result from adjusting the growth conditions are reported. Cross sectional TEM samples are prepared for observation along the <110> projection using standard mechanical polishing and dimple grinding, followed by argon-ion-milling (maximum beam energy 2.5 keV) with liquid-nitrogen cooling to reduce ion-beam damage. The electron microscopy was performed using a FEI CM-200 high-resolution electron microscope with an accelerating voltage of 200kV.The sample set examined consists of InAsSbBi layers grown at 1) 280 ºC with Bi/In flux ratio 0.065, 2) 400 ºC with Bi/In flux ratio 0.050, and 3) 430 ºC with Bi/In flux ratio 0.100. The sample structure crosssection is inset in Figure 1. The structural quality of growths 1 and 2 is examined using high resolution electron microscopy at low magnification (see Figures 1 and 2). The material is observed to be defect free over large lateral distances. The observation of contrast modulation in Figure 2 indicates the presence of composition inhomogeneity in InAsSbBi grown at the higher growth temperature. The upper interfaces are imaged using high resolution electron microscopy and shown in Figures 3 and 4. The interfaces are observed to be smooth and coherent with no misfit dislocations. The high quality interfaces are confirmed by the presence of Pendellösung fringes in X-ray diffraction measurements over large angular ranges (see Figure 6). For growth 3 at the highest temperature and highest Bi flux, the surface morphology significantly changes via the formation of surface droplets, as observed in the electron micrograph shown in Figure 5 [2].