Electronic States of P Donors in Si Nanocrystals Embedded in Amorphous SiO₂Layer Studied by Electron Spin Resonance: Hydrogen Passivation Effects

Abstract

Si nanocrystals (SiNCs) embedded in formed amorphous SiO 2 layer and P nanoscale doping have been investigated by electron spin resonance (ESR) measurements at low temperatures. Hydrogen atom treatment is found to be required to determine the proper doping effects and electronic states of doped donors and quasi-conduction electrons in SiNCs. The dependences of microwave power and temperature for the ESR hyperfine structure of isolated P donors indicate that the spin-lattice relaxation time T 1 becomes longer with decreasing size of SiNCs. From the experimental results of donor concentration and temperature dependence, we propose a novel model that the spin property of SiNCs of approximately 5.8 nm size is strongly dependent on the number of donors doped in a SiNC, i.e., odd or even. Using this model, we also estimate the numbers of P donors included in each SiNC to be 1 to at most 6, which are less than 1/10 of the average P doping concentrations.

Electron Excitation Memory Induced by Light Irradiation of Hydrogenated Si Nanocrystals Embedded in SiO2

“…This method is called hydrogen passivation in general, or hydrogen atom treatment (HAT) in our case. 12,25) The permeability or mobility of H atom is much higher than that of hydrogen molecules. 10,12) The electron spin resonance (ESR) measurements were done for the prepared samples at 4.2 K with and without laser light irradiation at each wavelength of 633, 532, and 442 nm.…”

“…7) Impurity doping is a key technology for SiNCs and SiNWs as well as for bulk Si in order to control electrical and optical properties. [8][9][10][11][12][13][14][15][16][17][18][19] Our recent study 10,12) revealed that proper hydrogen passivation is needed to obtain a better SiNCs/SiO 2 system with little interface defects and for the study of impurity doping and quasi-conduction electrons (QCE). In general, since the number of Si atoms contained in each SiNC with a diameter of 3 and 5 nm is estimated to be approximately 680 and 3100, the discrete levels in the quasiconduction band (QC-band) have a separation larger than an energy of 0.33 meV.…”

“…For SiNCs, odd or even numbers of QCE originating from electrically active P donors in a SiNC can be expected to yield entirely different magnetic property at lower temperatures such as 4.2 K. 12) If a SiNC is doped with a single donor or an odd number of donors, one unpaired spin survives even at extreme low temperatures resulting in significant enhancement of the paramagnetism. On the other hands, for a SiNC with an even number of donors, the paramagnetism becomes zero because of pairing of up-and down-spins at the lowest energy level of QC-band.…”

“…We reported previously that the number of P donors doped in a SiNC can be estimated to be 1-6 at most even when we used very high-level of P concentrations for preparation of P-doped SiNCs/SiO 2 systems. 12) This is caused by selfpurification and segregation effects during the formation of SiNCs embedded in SiO 2 . 8,12) With a correlation of the oddeven problem seen at low temperature, electron excitation memory is of interest for the future electron and magnetic devices.…”

“…12) This is caused by selfpurification and segregation effects during the formation of SiNCs embedded in SiO 2 . 8,12) With a correlation of the oddeven problem seen at low temperature, electron excitation memory is of interest for the future electron and magnetic devices. As for spin memory, for example nuclear spin memory has been reported through hyperfine interaction between nuclear spin and electron spin during photoexcitation of N-doped semiconductors 20) and conduction electron spin resonance of InP, 21,22) as well as d-electron spin memory of light-induced magnetization for Mn-doped CdSe dots.…”