Effect of Substrate Faceting on Epitaxial Lead Sulfide Thin Films Deposited from a Solution onto GaAs(100)

Abstract

Lead sulfide (PbS) thin films were deposited from a solution onto chemically etched GaAs substrates. The substrates were etched using two different chemical etchants, citric acid and phosphorous acid, resulting in different substrate roughness values from 0.4 nm up to 6.2 nm. In both cases, etching resulted in the simultaneous exposure of (100), (111), and (311) microfacets. These different substrate conditions had a strong impact on the morphology and microstructure of the PbS films. This work provides the first reported evidence for PbS thin films deposited onto GaAs(311) microfacets with {113}/⟨110⟩ twinning relations.

Effect of GaAs Substrate Micropatterning on Threading Dislocation Density in Solution-Deposited Lead Sulfide Thin Films

“…The primary distinction between PbS films deposited from solution on patterned GaAs(100) and GaAs(111)­A substrates is shown in Figure In the case of GaAs(100) the PbS film exhibits interruptions and distinct characteristics in the trench/line regions from those observed on the trench slopes (Figure a). Deposition within the trench/line regions occurs on smooth GaAs(100) facets, resulting in [001] PbS ∥[11̅0] GaAs zone axes and (1̅1̅0) PbS ∥(100) GaAs orientation relations (Figure b), in agreement with previous studies; heterotwinning is observed with a {111} twin plane and ⟨112⟩ twinning direction . In contrast, growth on the slopes takes place on GaAs(111) facets, giving rise to [11̅0] PbS ∥[11̅0] GaAs zone axes and (111) PbS ∥(111) GaAs orientation relations (refer to Figure c,e), creating heterotwinning relation {111}/⟨112⟩.…”

“…On the one hand, substrate roughness allows for an increased density of preferred nucleation sites per unit area. Furthermore, previous research has shown that alteration of the crystallographic characteristics of the GaAs surface due to chemical etching, which results in exposure of (111) facets, is accompanied by an increase in growth rate . These considerations lead to the conclusion that increased trench width (smaller density of prismatic facets) should have resulted in slower growth rate, yet our results show the opposite behavior.…”

“…Deposition of thin PbS films on GaAs opens the path for integration of PbS IR optoelectronics with GaAs-based technology and photothermal conversion applications. , Commonly used techniques for PbS films growth include reactive evaporation, spray pyrolysis, hot wall techniques, and vapor phase epitaxy, − however all these techniques are complicated and costly, while chemical solution deposition (CD) is a straightforward and low-cost technique for PbS film growth. Chemical epitaxy of PbS on GaAs has been shown to result in twin-like orientation relationship later shown to depend upon the crystallographic orientation of the substrate microfacet . The possibility to control the growth mechanism in the solution deposition of thin films provides important control over the film morphology, with implications for potential device performance.…”

“…In this mode, a crystal layer tends to complete before a new layer starts above it, resulting in a smooth and flat surface. Multiple studies employed the CD technique for depositing PbS thin films on both flat − and faceted GaAs substrates. The growth and morphology of the deposited film were found to be affected by the complexing agent, the concentrations of the bath components, temperature, pH, and more. ,,,, Gutman et al, demonstrated the fabrication of two-dimensional and three-dimensional photonic crystal achieved by deposition of nanocrystalline PbS within macroporous silicon. ,, However, those studies did not specifically investigate the impact of confinement shape and dimensions on epitaxial chemically grown PbS thin films.…”