Increased bismuth concentration in MBE GaAs1−xBix films by oscillating III/V flux ratio during growth

Abstract

Magnetic and transport properties of III-V based magnetic semiconductor (GaMn)As: Growth condition dependence Appl. Phys. Lett. 74, 398 (1999); 10.1063/1.123082 III-V based magnetic(GaMnAs)/nonmagnetic(AlAs) semiconductor superlattices Appl.The authors have examined bismuth concentration profiles in GaAs 1Àx Bi x films grown by molecular beam epitaxy using high angle annular dark field imaging (Z-contrast imaging) in an aberrationcorrected scanning transmission electron microscope in conjunction with x-ray diffraction. Samples were grown with a gradient in each of the component fluxes, and therefore, the III/V ratio across the substrate. Rotating the sample during growth exposed the growth surface to an oscillating III/V flux ratio. Sinusoidal [Bi] profiles resulted in the growth direction, the wavelength and number of which were consistent with the growth rate and the rate of substrate rotation. However, the magnitude of [Bi] in the observed fluctuations was greater than the maximum [Bi] achieved using the same Bi flux and Ga/As flux ratios in steady-state conditions on a stationary substrate, suggesting that varying the III/V flux ratio during growth promotes the incorporation of Bi in GaAs 1Àx Bi x films. A proposed qualitative model for how this enhancement might occur hypothesizes a critical role for alternating growth and shrinkage of Ga-Bi predroplet clusters on the surface as the growing material is rotated through Ga-rich and As-rich flux compositions.

Impact of in-situ annealing on dilute-bismide materials and its application to photovoltaics

“…Profiles of the STEM image intensity along lines extending from the GaAs buffer layer were generated in the same way as described in Ref. [16]. The cross-sectional STEM sample was prepared by the wedge-polishing method, followed by Ar ion milling.…”

Droplet-mediated formation of embedded GaAs nanowires in MBE GaAs1−xBixfilms

“…The GaAs 1−x Bi x films were grown at T g =320 °C with Bi beam-equivalent-pressures (BEP) of 1.2 ×10 −8 Torr and Ga and As 2 BEPs of 1.0×10 −7 Torr and 9.8×10 −7 Torr, respectively. The positions of the effusion cells in the MBE chamber cause a spatial variation in the fluxes such that the normalized Ga/As flux ratio varies approximately linearly across the 28 mm of potential growth surface from 0.77 in the As-rich region, to 1.77 in the Ga-rich region, as detailed in [5]. Growth inhomogeneities that might result typically are mitigated by substrate rotation.…”

“…Depending on growth conditions, droplets of pure Bi or Ga-Bi have been observed on the surface of GaAsBi alloys [2][3][4]. It has been suggested that these droplets play a critical role in the incorporation of Bi into the film during growth [5]. Previous studies have largely focused on the composition and structure [3], and/or the connections between growth conditions and droplet formation [6][7][8].…”

GaAsBi: From Molecular Beam Epitaxy Growth to Devices

“…In 2015, Wood et al showed that oscillating flux ratios can produce enhanced Bi contents. [ 122 ] They attributed this to a periodic accumulation and crystallization of surface Ga droplets and a resulting vapor–liquid–solid incorporation pathway. This study was performed at 320 °C and observed average Bi contents of ≈3%—far lower than the limit imposed by the growth temperature (see Figure 7).…”