Optical anisotropy of CuPt-ordered GaAsBi alloys

Abstract

The molecular beam epitaxy-grown epitaxial, partially relaxed, GaAsBi x bismide layers of thickness and x ≈ 0.04 composition are examined. The atomic-structure analysis by x-ray diffraction and transmission electron microscopy shows the bismides to be CuPt-type atomic-ordered in both and subvariants. The ordering induces an optical anisotropy, which manifests at normal incidence light-beam propagation. The anisotropy is revealed by various optical spectroscopy techniques—polarized photoluminescence, photo-modulated transmittance and reflectance, polarized transmittance, and spectroscopic ellipsometry. The ordering-induced valence band splitting, determined from modulation spectroscopy measurements, is of about . The splitting is comparable to that in CuPt-ordered conventional III–V semiconductor alloys even though the maximal ordering parameter in investigated bismides is one order of magnitude lower.

Understanding Growth‐Faulted GaAsBi Samples by Reflectance Anisotropy Spectroscopy

“…[30,31] An intriguing explanation is the presence of CuPt ordering in the bulk, naturally inducing optical anisotropy for light at normal incidence on the (001) plane. The existence of such a CuPt ordering in MBE grown GaAsBi samples has been reported in literature: [37][38][39] some of these papers remarkably present results of optical spectroscopy techniques. [37,38] It is possible to outline a list of the main characteristics of such a structure: 1) it is bulk-related; 2) it scales with the Bi concentration in the crystal; 3) the sign (that is its dependence upon crystallographic directions) shows a preferential orientation along the [110] direction, except for samples under tensile strain or no strain with Bi concentration of 7% (see curves 1b and 1c in Figure 1); 4) the energy position is not constant, but in high-quality samples ranges between 2.2 and 2.5 eV; and 5) the lineshape is roughly compatible with a single peaked structure (whose full width at half maximum is about 0.5-0.6 eV), although in some cases a shoulder appears at lower photon energy (see, e.g., curve 1c in Figure 1).…”

“…[ 30,31 ] An intriguing explanation is the presence of CuPt ordering in the bulk, naturally inducing optical anisotropy for light at normal incidence on the (001) plane. The existence of such a CuPt ordering in MBE grown GaAsBi samples has been reported in literature: [ 37–39 ] some of these papers remarkably present results of optical spectroscopy techniques. [ 37,38 ]…”

Sensing Sub‐Surface Strain in GaAsBi(001) Surfaces by Reflectance Anisotropy Spectroscopy

“…[15] The importance of optical techniques when applied to MBE-grown GaAsBi alloys is also confirmed through remarkable experiments investigating strain-engineered bismides deposited on thin step-graded InGaAs buffer layers, [35] exploiting the relationships of polarized photoluminescence measurements with the bulk ordering. [36,37] The use of strain-engineering to tune the electronic properties of matter and then customize solid-state materials via a controlled deformation, offers intriguing possibilities to modulate the band structure and consequently ignite new electronic and optical properties, as in 2D materials [38,39] and in quantum dots. [40] Optical techniques (RAS, [15,17] photoluminescence [35][36][37] ) provide the opportunity of measuring directly and in a quite simple way the strain condition present in the sample.…”

“…[36,37] The use of strain-engineering to tune the electronic properties of matter and then customize solid-state materials via a controlled deformation, offers intriguing possibilities to modulate the band structure and consequently ignite new electronic and optical properties, as in 2D materials [38,39] and in quantum dots. [40] Optical techniques (RAS, [15,17] photoluminescence [35][36][37] ) provide the opportunity of measuring directly and in a quite simple way the strain condition present in the sample.…”

Low-Frequency Noise Characteristics of (Al, Ga)As and Ga(As, Bi) Quantum Well Structures for NIR Laser Diodes

“…On the other hand, the weaker band gap sensitivity to the temperature of the Ga(As, Bi) enables a more stable operation of the Ga(As, Bi)-based LD without external cooling. However, the introduction of Bi into the GaAs system also has several disadvantages: technological problems related to the low-temperature growth process, Bi surface segregation, formation of Bi clusters, and CuPt-type Bi distribution [ 8 , 9 , 10 ]. To facilitate Bi incorporation and avoid segregation, the structures need to be grown at low temperature and with significantly reduced arsenic fluxes.…”