Compound semiconductor alloys: From atomic-scale structure to bandgap bowing

Abstract

Compound semiconductor alloys such as InxGa1−xAs, GaAsxP1−x, or CuInxGa1−xSe2 are increasingly employed in numerous electronic, optoelectronic, and photonic devices due to the possibility of tuning their properties over a wide parameter range simply by adjusting the alloy composition. Interestingly, the material properties are also determined by the atomic-scale structure of the alloys on the subnanometer scale. These local atomic arrangements exhibit a striking deviation from the average crystallographic structure featuring different element-specific bond lengths, pronounced bond angle relaxation and severe atomic displacements. The latter, in particular, have a strong influence on the bandgap energy and give rise to a significant contribution to the experimentally observed bandgap bowing. This article therefore reviews experimental and theoretical studies of the atomic-scale structure of III-V and II-VI zincblende alloys and I-III-VI2 chalcopyrite alloys and explains the characteristic findings in terms of bond length and bond angle relaxation. Different approaches to describe and predict the bandgap bowing are presented and the correlation with local structural parameters is discussed in detail. The article further highlights both similarities and differences between the cubic zincblende alloys and the more complex chalcopyrite alloys and demonstrates that similar effects can also be expected for other tetrahedrally coordinated semiconductors of the adamantine structural family.

Ion-implantation-induced amorphization of InxGa1−xP alloys as functions of stoichiometry and temperature

“…This bimodal bond length distribution in In x Ga 1Àx P (and many III-V alloys) can be accommodated by bond stretching, bond bending, or a combination of the two and force constants determine the dominant contribution. 10 Cai and Thorpe 7,39 defined a topological rigidity parameter (a**), where values of 0 and 1 correspond to, respectively, bond stretching only and bond bending only. (The Vegard model is characterized by a** ¼ 0.)…”

“…Like In x Ga 1Àx As, In x Ga 1Àx P exhibits a bimodal bondlength distribution as predicted theoretically 7 and demonstrated experimentally. [8][9][10] For In x Ga 1Àx As implanted at 300 K, we previously reported that the ternary alloys were easier to amorphize than their binary end members 11 and attributed this unanticipated behavior to a stimulated amorphization process, the latter enhanced by the presence of structural disorder resulting from the bimodal bond-length distribution. For this report, we have studied the amorphization kinetics of In x Ga 1Àx P as functions of both implantation temperature and stoichiometry to determine whether the influence of a bimodal bond-length distribution is particular to In x Ga 1Àx As or common to other ternary III-V alloys.…”

First-principles quantitative prediction of the lattice thermal conductivity in random semiconductor alloys: The role of force-constant disorder

“…In this medium, alloy atoms are placed in the exact same environment as they have in the parent compounds and bond distances are simply assumed to depend linearly on the alloy concentration. In contrast, experimental observations have found that the atomic-scale structure of semiconductor alloys is actually characterized by large fluctuations from the average-medium structure of the VCA [6]. The presence of this structural disorder at the atomic scale will greatly affect the material's IFCs in a way that cannot be modeled by simply averaging over the pure-compound IFCs.…”

“…Random semiconductor alloys are receiving a considerable amount of attention due to their central role in a wide range of technologies, such as photonics [1,2], electronics and optoelectronics [3][4][5]. It has been observed that important physical quantities, such as the cell parameters and electronic band gap, can be made to vary continuously between the limiting values of the parent compounds [6], making the possibility of tuning the alloy properties through the component concentrations of particular interest.…”

“…In this contribution, we take cubic In 1−x Ga x As, which presents many features common to general III-V semiconductor alloys [6], as an example. Extended X-rayabsorption fine-structure (EXAFS) measurements clearly show that the Ga − As and In − As nearest-neighbor (NN) distances in In 1−x Ga x As are mostly unaffected by the alloy concentration and assume the same values as in the parent compounds [23].…”