Size dependence of phosphorus doping in silicon nanocrystals

Abstract

Doping of silicon nanocrystals (Si-NCs) is one of the major challenges for silicon nanoscale devices. In this work, phosphorus (P) doping in Si-NCs which are embedded within an amorphous silicon matrix is realized together with the growth of Si-NCs by plasma-enhanced chemical vapor deposition under a tunable substrate direct current (DC) bias. The variation of phosphorus concentration with substrate bias can be explained by the competition of bonding processes of Si-Si and P-Si bonds. The formation of Si-Si and P-Si bonds is differently influenced by the ion bombardment controlled by the substrate bias, due to their bonding energy difference. We have studied the influences of grain size on P doping in Si-NCs. Free carrier concentration, which is provided by activated P atoms, decreases with decreasing grain size due to increasing formation energy and activation energy of P atoms incorporated in Si-NCs. Furthermore, we have studied the P locations inside Si-NCs and hydrogen passivation of P in the form of P-Si-H complexes using the first-principles method. Hydrogen passivation of P can also contribute to the reduced free carrier concentration in smaller Si-NCs. These results provide valuable understanding of P doping in Si-NCs.

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“…The P 2p spectra shown in Figure b, specify the position of the heavily doped P located at 135.4 eV in the bulk-doped substrate; this peak corresponds to P–O (∼34%) . In the DNP case, the P–O decreases, and a new peak at 129.5 eV appears, which corresponds to Si–P . For DNP manufactured at a high ionization rate, the peak at Si–P is ∼9.38% (high), and P–O is ∼3%.…”

“…Further, for other poorly/lightly doped DNP, the vacancy state varies from 9 to 12%, as shown in Figure S2b. Also presented in Figure d is the Si 2p, where the peak at 102.9 eV is attributed to Si–O in NP. , This peak is red-shifted in DNP compared to UDNP. The peak at 99 eV corresponds to the Si–Si bond in the bulk-doped substrate.…”

“…These results demonstrate that a high ionization rate is essential to overcome the substrate’s threshold to ionize the P from the substrate and embed itself within the Si crystal during fast condensation. Investigating O 1s in Figure c, the peak at 523 eV corresponds to Si–O, and the deconvoluted high-energy peak at 534.5 eV corresponds to adsorbed oxygen species or vacancy states. , The DNP with high Si–P showed very low vacancy of 7%, and this concentration increases to 21% in undoped NP. Here, weak vacancy states are observed in the bulk substrate.…”

Effect of Doping with Shallow Donors on Radiative and Nonradiative Relaxation in Silicon Nanocrystals: Ab Initio Study

“…Various aspects of physics of doped silicon nanocrystals have been already studied, especially for the case of doping with boron or phosphorus, ,,− ,− or codoping with boron and phosphorus. ,, In particular, the formation energy, , electronic structure, ,− radiative recombination rates, ,, absorption spectra, , etc. have been calculated by different methods.…”

“…An additional reconstruction of the electronic structure of Si crystallites can be obtained with various methods such as formation of crystallites in different dielectric matrices; − surface chemistry; − introduction of shallow impurities; − etc. As shown in a number of theoretical , and experimental , works, some kinds of nanocrystals covering can significantly intensify the electron–hole radiative transitions and enhance the photoluminescence intensity.…”