Borane radicals reactions with the Si surfaces and related electronic properties of the products from first-principles

Significance 

Modern physics is rapidly advancing. Essentially, it entails efforts to understand the underlying processes of the interactions with matter through the utilization of the tools of science and engineering. For instance, recent publications have reported on the development of novel technologies, such as micro-photolithography and nanoelectronics, that demand high-performance radiation detectors for, e.g. NUV (near ultra-violet) or VUV (vacuum ultra-violet) photons. The NVU/VUV photons have an extremely small penetration depth of the NUV/VUV radiations . This therefore, requires the depletion zone of the photodiode to be very close to the device surface. This shortfall has been recently circumvented through the development of the PureB process; a process that involves pure amorphous boron (a-B) deposition on crystalline Si (c-Si) to produce c-Si/a-B junctions by means of chemical vapor deposition (CVD) of diborane (B2H6). Recent study also showed that PureB process produces c-Si/a-B interfaces with little Si-B mixing at low temperature (~400 °C) at which the Si wafer surface is dominated by the Si {001}3 × 1 domains that consist of two different Si species at low temperature. Nonetheless, the reactions of the dilute BHn (n = 0 to 3) radicals on Si surfaces is not yet well understood. Therefore, knowledge, particularly concerning its electronic properties on the Si surfaces, is vital for understanding the underlying physics.

So far, previous research reveals that experimentalists have focused on the structure of the diborane molecule and its decomposition reactions. In a prior work, researchers from the TU Delft in the Netherlands: Dr. Vahid Mohammodi, Professor Stoyan Nihtianov and Professor Marcel Sluiter together with Dr. Changming Fang at the Brunel University London, investigated deposition of BHn (n = 0 to 3) radicals on the Si {001}2 × 1:H surface which is stable at high temperature (~640 °C) [1]. In a new research study they further examined the geometry, stability and electronic properties of the hydrogen passivated Si{001}3 × 1 surfaces with deposited BHn (n = 0 to 3) radicals using parameter-free first-principles approaches. Their work is currently published in the Journal of Physics: Condensed Matter [2].

In their approach, the team engaged in first-principles calculations that produced details of the optimized structures and related energetics for BHn radicals on the Si {001}3 × 1:H surface, and also provided a static picture about the initial stage of PureB process. Moreover, the Ab initio molecular dynamics (AIMD) technique was also employed to model the processes of BH3 depositing on the Si {0 01}3 × 1:H surfaces.

The authors reported that their approach revealed the importance of the van der Waals correction to the standard DFT functional in description of molecular/surface interactions. The team also noted that the structural optimizations provided strong local relaxation and reconstructions at the deposited Si surface. Moreover, electronic structure calculations revealed the formation of various defect states in the forbidden gap.

In summary, the study reported on the AIMD simulations for diborane molecules on the H passivated Si {001} surfaces, that revealed the atomistic details of deposition of diborane and the corresponding formation of –SiBH4 radicals on the surfaces. Going by their results and discussions, the authors highlighted that their results could potentially enhance our understanding of the initial stage of the PureB process and the electric properties of the products. In a statement to Advances in Engineering, the authors further emphasized that the findings could aid in developing new PureB processes for new heterojunctions for detection of UV photons.

Borane radicals reactions with the Si surfaces and related electronic properties of the products from first-principles - Advances in Engineering
Quantum-mechanics based density-functional theory calculations reveal preference of absorption of BHn (n = 2 and 3) radicals on Si surfaces at the initial stage of PureB process.

References

[1] C M Fang, V Mohammodi, S Nihtianov, M H F Sluiter, Stability, local structure ad electronic properties of borane radicals on the Sii(1 0 0)2 × 1:H surface: A first-principles study, Computational Materials Science 140 (2017) 253-260.

[2] C M Fang, V Mohammodi, S Nihtianov, M H F Sluiter. Stability, geometry and electronic properties of BHn (n = 0 to 3) radicals on the Si {0 0 1}3 × 1:H surface from first-principles. Journal of Physics: Condensed Matter, volume 32 (2020) 235201 (10pp)

Go To Journal of Physics: Condensed Matter

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