The effect of implantation dose on the microstructure of silicon nanocrystals in SiO₂

Abstract

Si nanocrystals were formed by the implantation of Si+ into a SiO2 film, deposited on (100) Si, followed by high-temperature annealing. Transmission electron microscopy (TEM) was used to examine the effect of implantation dose on the microstructure of the Si nanocrystals (Si nc) in the SiO2 film. The size and spatial distribution and concentration of the Si nc in four passivated samples with different implantation doses were investigated using the dark-field imaging technique. The thickness of all the samples was determined by electron energy-loss spectroscopy (EELS). The structure of the Si nc in all the samples was determined using selected area electron diffraction. It was found that the average diameter of the Si nc changes from 2.7 to 3 and to 3.3 nm for the samples with implantation doses of 6 × 1016, 8 × 1016 and 1 × 1017 cm−2; however, it ranges from 2 to 22 nm in the sample with an implantation dose of 3 × 1017 cm−2. The size of the Si nc is comparatively homogeneous throughout the whole implanted layer in the samples with implantation doses of 6 × 1016 and 8 × 1016 cm−2, while in the samples with implantation doses of 1 × 1017 and 3 × 1017 cm−2, the Si nc in the middle region of the implanted layer are bigger than those near the surface or the bottom of the layer. From TEM experimental results, the concentration of the Si nc is estimated to be 6 × 1018, 4 × 1018 and 4 × 1018 cm−3 for the samples with implantation doses of 6 × 1016, 8 × 1016 and 1 × 1017 cm−2, respectively. For the sample with an implantation dose of 3 × 1017 cm−2, the concentration for the Si nc of 3 nm is around 5 × 1018 cm−3; the concentration for Si nc of 6 nm is around 2 × 1018 cm−3; and the concentration for the 12 nm group is about 1 × 1018 cm−3. In addition, the concentration determined from TEM experiments is compared with the calculated one. Combining the TEM results with a Monte Carlo simulation, we also discuss the sputtering effect and the depth distribution of the Si ions implanted in SiO2.

The formation mechanism of Si nanocrystals in SiO2

“…For the specimen annealed for 1 h, from the dark field imaging [6], it has been shown that Si nc range from 2 to 22 nm in diameter, and the nanocrystals in the middle region of the layer are bigger than those near the free surface or the bottom of the layer. From HRTEM studies [7], it has been revealed that most of Si nc smaller than 5 nm are spherical and defect free, while twinning and stacking faults are dominant in the large nanoparticles.…”

“…Various methods have been used to produce luminescent thin films containing Si nc [1][2][3][4][5]. Ion implantation is one of the most promising fabrication methods for Si nc embedded in SiO 2 because it allows the possibility of controlling the size, depth profile and concentration of Si nc, albeit not independently [6]. However, the mechanism underlying light emission from this system is still controversial.…”

Stacking Fault Energy of Si Nanocrystals Embedded in SiO2

“…Figure 1(a) shows a typical cross-sectional DF image of this specimen [5]. From Figure 1(a), it can be seen that the Si nc layer extends from 50 ± 5 nm to a maximum depth of 290 ± 10 nm, and the size ranges from 2 to 22 nm in diameter.…”

About the Temperature Dependence of Photoluminescence of Silicon Quantum Dots

“…Постимплантационный отжиг осуществляли в пото-ке N 2 при температуре 1100 °С в течение 2 ч. Согласно многочисленным литературным данным [1] и резуль-татам, полученным авторами ранее [11], выбранные режимы обеспечивают формирование в пленках SiO 2 массивов НК кремния, излучающих свет с длинами волн 650-1000 нм. Данные электронной микроско-пии, представленные в научно−технической ли-тературе (см., например, работу [12]) для образцов, полученных в близких режимах, свидетельствуют о том, что средний размер НК кремния возрастает при увеличении дозы (от значений ~ 3 нм для дозы Si + 5 · 10 16 см −2 до 12 нм для дозы 3 · 10 17 см −2 ).…”