The electronic properties of unstrained unrelaxed InAs _x Sb_1−x alloys have been determined in a wide range of alloy compositions using IR magnetospectroscopy, magnetotransport and IR photoluminescence. All studied alloys have n-type background doping with electron concentration decreasing with the Sb content. The composition dependence of the background doping concentration follows an empirical exponential law in a wide range of compositions. Both bandgap and electron effective mass dependence on alloy composition exhibit negative bowing reaching lowest values at x = 0.63: E _g = 0.10 eV, m* = 0.0082 m ₀ at 4.2 K. The bowing coefficient of 0.038 m ₀ obtained for the electron effective mass is in good agreement with that obtained from the Kane model.

Realizing a large Landé g-factor of electrons in solid-state materials has long been thought of as a rewarding task as it can trigger abundant immediate applications in spintronics and quantum computing. Here, by using metamorphic InAsSb/InSb superlattices (SLs), we demonstrate an unprecedented high value of g ≈ 104, twice larger than that in bulk InSb, and fully spin-polarized states at low magnetic fields. In addition, we show that the g-factor can be tuned on demand from 20 to 110 via varying the SL period. The key ingredients of such a wide tunability are the wavefunction mixing and overlap between the electron and hole states, which have drawn little attention in prior studies. Our work not only establishes metamorphic InAsSb/InSb as a promising and competitive material platform for future quantum devices but also provides a new route toward g-factor engineering in semiconductor structures.

Band gap is known as an effective parameter for tuning the Landé $g$ factor in semiconductors and can be manipulated in a wide range through the bowing effect in ternary alloys. In this work, using the recently developed virtual substrate technique, high-quality InAsSb alloys throughout the whole Sb composition range are fabricated and a large $g$ factor of $g\approx -90$ at the minimum band gap of $\sim 0.1$ eV, which is almost twice that in bulk InSb, is found. Further analysis to the zero gap limit reveals a possible gigantic $g$ factor of $g\approx -200$ with a peculiar relativistic Zeeman effect that disperses as the square root of magnetic field. Such a $g$-factor enhancement toward the narrow gap limit cannot be quantitatively described by the conventional Roth formula, as the orbital interaction effect between the nearly triply degenerated bands becomes the dominant source for the Zeeman splitting. These results may provide insights into realizing large $g$ factors and spin-polarized states in semiconductors and topological materials.

A Dirac-type energy spectrum was demonstrated in gapless ultrashort-period metamorphic InAsSb/InSb superlattices by angle-resolved photoemission spectroscopy (ARPES) measurements. The Fermi velocity value of 7.4 × 10⁵ m/s in a gapless superlattice with a period of 6.2 nm is in good agreement with the results of magnetoabsorption experiments. An “inverted” bandgap opens in the center of the Brillouin zone at higher temperatures and in the superlattice with a larger period. The ARPES data indicate the presence of a surface electron accumulation layer.

The sources of temperature sensitivity of the threshold current in type-I and type-II mid-infrared semiconductor lasers are investigated. Measurements of the interband optical absorption allow direct comparison of the optical matrix elements in laser structures with type-I and type-II band alignments and prove that the difference in the optical matrix elements is insignificant for these two groups of structures. We show that thermally-induced hole escape from the active quantum wells strongly deteriorates the optical emission in both type heterostructures. Experiments show that the temperature decay of PL is generally stronger for type-II samples.