Growth and Size Control of Amorphous Silicon Quantum Dots Using SiH4/N2 Plasma

Abstract

Recently, the optical properties of Si nanostructures have been the subject of intensive study. The strong photoluminescence (PL) from porous Si, [1,2] Si nanocrystals, [2,3] and amorphous Si quantum structures [4±6] prepared by a variety of methods has been the subject of particular attention from both the fundamental and practical points of view. Although several emission mechanisms from Si, including quantum size effect, defects, and Si-based chemical species such as siloxane and polysilane, have been proposed, [7±10] quantum size effect has been most frequently proposed as the origin of the PL, and the size control of Si quantum structures is an important factor in Si-based optoelectronic devices. Most studies have been focused on quantum wells [11±13] and self-assembled Si quantum dots (QDs) grown on an insulating surface [14±16] for the size control of Si quantum structures. However, these self-assembled Si QDs have a large lateral size, and the quantum size effect is negligibly small in the lateral direction compared to that of sphere-like QDs. Therefore, quantum well and self-assembled Si QD structures grown on the substrate are not suitable for optoelectronic applications in the short wavelength region because quantum size effect in these two structures is very small due to only one-dimensional size effect in the growth direction.Meanwhile, amorphous Si (a-Si) has two important advantages compared with bulk crystalline Si. Firstly, the luminescence efficiency of bulk a-Si is higher than that of crystalline Si because of its structural disorder. [17] In addition, the bandgap energy of bulk a-Si (1.6 eV) is larger than that of bulk crystalline Si (1.1 eV), thus making it a good candidate for short-wavelength device applications such as a blue light-emitting diode. Therefore, it would be expected that these intrinsic advantages of a-Si and the quantum confinement effect in the a-Si QD in three directions would lead to extremely useful optical properties in short-wavelength devices. [18] In this study, a silicon nitride film was used as a matrix material to embed a-Si QDs. A silicon nitride film is expected to be better than silicon oxide in optical device applications because carriers can be easily transported to the a-Si QDs in the silicon nitride matrix due to the lower tunneling barriers for electrons and holes of silicon nitride than those of silicon oxide. [11] We report here on the growth and size control of a-Si QDs embedded in the silicon nitride film by plasma enhanced (PE) CVD. Figure 1 shows the Raman spectrum, that can be separated into two components. One peak in the vicinity of 460 cm ±1 is assigned to the asymmetric Si±N bond stretching mode in the silicon nitride matrix, and the other peak in the vicinity of 490 cm ±1 corresponds to scattering with localized optical phonons that exist in silicon QDs surrounded by nitrogen atoms. [19] Compared to those from bulk materials, these two peaks are also shifted to the highenergy side by about 10 cm ±1 , due to the compressive strain normally p...

Photoluminescence and optical absorption properties of silicon quantum dots embedded in Si-rich silicon nitride matrices

“…The increase in R appears to promote the dissociation of Si-H bands, resulting in an increase in silicon atoms having dangling bonds. The increase in dangling bonds of silicon atoms is believed to facilitate the creation of nucleation sites and the formation of silicon clusters in the silicon nitride film during the growth process [15,16]. Therefore, the size of the silicon clusters decreases with increasing the gas flow ratio.…”

Photoluminescence analyses of hydrogenated amorphous silicon nitride thin films

“…Since all of these peaks are associated with Si-N bonds in different configurations [16], they were named as Si-N (n 1 ,n 2 ,n 3 ). The vibration bands at 1170 and 3350 cm À 1 are assigned to the N-H rocking and stretching modes, respectively [6]. The peaks at 660 and 2170 cm À 1 are attributed to the Si-H wagging and stretching bonds, respectively [6,16].…”

“…The luminescent active layer of Si based LEDs can be produced by various methods: ion implantation [3], sputtering [4], laser ablation [5], plasma enhanced chemical vapor deposition (PECVD) [6]. Among these techniques, PECVD, which renders low temperature thin film growth over large areas, is suitable for both macro-and microapplications.…”

Effect of hydrogen passivation on charge storage in silicon quantum dots embedded in silicon nitride film

“…The use of additional N 2 gas was very critical to the growth of Si QDs in the silicon nitride films. 7,10 In this work, we investigated the influence of hydrogen incorporation on the charging and the charge retention characteristics of silicon nitride films containing Si QDs grown using two different gas mixtures.…”

“…Details of the sample preparation have been described elsewhere. 10 In order to measure the capacitance-voltage ͑C -V͒ and capacitance-time ͑C-t͒ characteristics, metalinsulator-semiconductor ͑MIS͒ structures were fabricated. Figure 1͑a͒ shows photoluminescence ͑PL͒ spectrum of the two types of samples at room temperature.…”