Abstract
This paper is dedicated to study the thin polycrystalline films of semiconductor chalcogenide materials (CdS, CdSe, and PbS) obtained by ammonia-free chemical bath deposition. The obtained material is of polycrystalline nature with crystallite of a size that, from a general point of view, should not result in any noticeable quantum confinement. Nevertheless, we were able to observe blueshift of the fundamental absorption edge and reduced refractive index in comparison with the corresponding bulk materials. Both effects are attributed to the material porosity which is a typical feature of chemical bath deposition technique. The blueshift is caused by quantum confinement in pores, whereas the refractive index variation is the evident result of the density reduction. Quantum mechanical description of the nanopores in semiconductor is given based on the application of even mirror boundary conditions for the solution of the Schrödinger equation; the results of calculations give a reasonable explanation of the experimental data.
Highlights
Chemical bath deposition (CBD) is a cheap and energyefficient method commonly used for the preparation of semiconductor films for sensors, photodetectors, and solar cells
For CBD-made materials obtained after long deposition time, we observed a blueshift of the fundamental absorption edge relative to the bulk material data [16] in all cases with the following shift values: 0.06 eV for CdS [7], 0.15 eV for CdSe [6], and 0.1 to 0.4 eV for different samples of PbS (Figure 2)
The blueshift in the dense CBD films is attributed to the quantum confinement in pores
Summary
Chemical bath deposition (CBD) is a cheap and energyefficient method commonly used for the preparation of semiconductor films for sensors, photodetectors, and solar cells It was one of the traditional methods to obtain chalcogenide semiconductors including CdS and CdSe [1-6]. The crystallite size becomes larger so that the corresponding blueshift decreases Another feature characteristic to the process is a considerable porosity [3,9] inherent to the growth mechanism, which takes place ion by ion or cluster by cluster depending on the conditions or solution used (see [11,12]). We present the experimental results for the investigation of porosity effects for relatively large deposition times upon the optical characteristics of CBD-made semiconductor materials such as CdS, CdSe, and PbS. We show that the same treatment of pores allows to achieve a good correlation between theorical and experimental data
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