CC BY
7
https://doi.org/10.29013/ESR-22-5.6-42-45
Utamuradova Sharifa Bekmuradovna, Doctor of Physical and Mathematical Sciences, director of Research Institute of semiconductor physics and microelectronics Naurzalieva Elmira Mahambetyarovna, PhD student of Research Institute of semiconductor physics and microelectronics
RAMAN SPECTROSCOPY OF STRUCTURAL DEFECTS RELATED WITH SILVER ATOMS IN SILICON
Abstract. Vibrational and structural properties of silicon doped with silver atoms were investigated using Raman spectroscopy. It has been established that the introduction of silver atoms in silicon increases the interatomic distance in the crystal lattice, which, in turn, shifts the positions of the vibration peak to lower ones.
Keywords: Raman Spectroscopy, silver, interstitial and substitutional defects.
Introduction. It is known that the technological substitutional atoms; ii) I-interstitial states (fig. 1). For
route for the manufacture of almost any semiconductor device is accompanied by various cycles oflow- and high- temperature treatments, which inevitably leads to the formation ofvarious kinds ofstructural defects and impurity centers, as well as to the degradation ofdevice parameters. The degradation of the device parameters based on silicon structures to some extent depends on uncontrolled impurities - oxygen, carbon, metals that are in the silicon wafer or introduced during the manufacture ofdevices. Ofall the contact impurities (Cu, Al, Au, Ag, etc.) - silver is one of the available metals [1].
It is known from theory that the diffusion mechanism allows impurity atoms to be in two states: i) S-
example, the authors Rollert et al. [2] showed that the overwhelming majority ofAg impurity atoms are present at interstitial sites (AgI); and that substitutional silver (AgS) either does not occur or occurs only in very low concentrations. Using EPR studies, the authors of [3] identified this isolated Ag, which represents only a small fraction of the total amount of impurity silver atoms present. Today, there is no clear picture of the microscopic structure of defects related with silver atoms in silicon. Thus, the topic of this work is relevant and promising in terms of using its results.
In this paper, the surface states of silver atoms in silicon are considered by Raman spectroscopy.
Figure 1. Distribution of impurity atoms in silicon crystal
Experimental technique. Samples of n-type silicon (p — 7.5Q cm, ND « 6 -1014 cm grown by the Czochralski method were selected for measurement. Doping of the silver impurity was carried out by the diffusion method at a temperature of 1200 °C for 2-10 hours. The complete solubility of silver atoms in silicon at this temperature is achieved up to ~ 6.5 • 1015 cm-3. Raman spectra were obtained on an Ocean Optics QE65 Pro spectrometer with a 785 nm laser and an integration time of 500 ms.
Raman spectroscopy has proven to be a key experimental technique due to its ability to identify structural and electronic effects in non-destructive measurements. Raman spectroscopy, a fast and convenient method for study of the vibrational and structural properties of materials, is widely used to investigate the structures of crystalline and amorphous silicon semiconductors [4]. Raman scattering can measure changes in vibrational frequencies induced by the microstructure or the presence oflocal deformations, which can be produced by distortion of the bond angle. In this paper, the surface states of
silver and gadolinium atoms in silicon are considered by Raman spectroscopy. Raman spectroscopy studies vibrational energy levels by looking at the energy difference between laser light incident on the sample and the rare photon scattered inelastically via the Raman effect. This energy difference, known as the Raman shift, is reported in energy units called wavenumbers (cm-1).
The following equation shows how to calculate a Raman shift, Av, in cm1 using the laser wavelength (A0) and a Raman peak wavelength (lx) in nm:
Av (cm 1) =
107
cm
X0(nm) Xx (nm) Results and its discussion. The Raman spectra of the light of the initial sample Si<P> and doped with silver atoms Si<Ag> are shown in (fig. 2. and fig. 3).
The Raman spectrum of Si exhibits a high peak in the region 519-521 cm-1 with a FWHM of 8-12 cm-1. Intensity of first-order scattering due to optical phonons (TO, LO) at the central point r of the Brillouin zone.
Si
TO+LO
Si
TA
Si<P>
100 200 300 400 500 600 700 Raman shift (cm-1)
800 900 1000
Figure 2. Raman shift of initial silicon. Modes: SiTA - 215 cm-1, Sim - 412-494 cm-1, SiTn+m - 521 cm-1
TO+LO
100
200
300
400
500
600
700
800
900
1000
Raman shift (cm-1)
Figure 3. Raman shift of silicon doped with silver atoms. Modes:
SiTA - 221 cm-1, Sim - 414-504 cm-1, SiT
520 cm-
13
co
cn c (D
180
200
220
240
260
280 300 320-340 360
Raman shift (cm-1)
Figure 4. Gauss distribution of acoustic mode (TA) of Si<Ag> sample:1-214cm-1, 2-253 cm-1, 3-294 cm-1, 4-330 cm1
In contrast to the main peak, one can observe the fig.3, further doping of n-Si single crystals with
scattering by acoustic phonons at 221 cm-1 (2TA). silver impurity atoms leads to some change in the
The authors of [5] attribute such oscillations to the Raman spectra. When comparing the Raman spectra intrinsic Si interstitial defect. As can be seen from of the Si<P> and n-Si<Ag> samples, it can be seen
that after doping with Ag atoms, some of the silicon atoms (Sis) leave the crystal sites, which leads to a slight decrease in the intensity of the fundamental vibration (TO) at 520 cm-1.
Compared to the acoustic phonon peak of the second order of the Si<P> sample at 221 cm-1, which describes the interstitial nature of the crystal [5], the corresponding Raman peak in the Si<Ag> sample has an increased intensity, its line width is broadened, and the line shape becomes asymmetric with a small tail on the low energy side extending to 346 cm- 1 (Fig. 3). The Gaussian distribution ofthis peak showed several scattering peaks at 214, 253, 294, 330 cm-1, which is shown in (fig. 3). Analyzing the results of many publications
[2; 5], this modification can be explained by an increase in the concentration ofinterstitial defects (SiI, AgI, SiO2, etc.) after silver doping in silicon, which is caused by an increase in the intensity of the 221 cm-1 peak.
Conclusion. Thus, the processes of Raman scattering of light in silicon doped by diffusion with silver impurities have been studied. It has been shown that an increase in the concentration of interstitial defects in silicon doped with silver atoms leads to an increase in the intensity of the 221 cm-1 peak. It was also found that in this mode at 221 cm-1 have four components with Raman shift at 214, 253, 294, 330 cm-1 which can form nanodefects with self-interstitial impurities of silicon.
References:
1. Vincent T. M. and Estreicher S. K.J. Appl. Phys.- 128. 2020.- 155703 p. URL: https://doi.org/ 10.1063/5.0026161
2. Rollert F., StolwijkN. A. and Mehrer H.,J. Phgs.- D20. 1987.- 1148 p.
3. Son N. T., IKustov V. E., Gregorkiewicz T. and Ammerlaan C-A-J-, J. Appt. Phgs.- 73. 1993.- 1797 p.
4. Rong-ping Wang, Guang-wen Zhou, Yu-long Liu, et. al. "Raman spectral study of silicon nanowires: High-order scattering and phonon confinement effects". Phys. Rev. B,- 61 (24). 2000.- P. 16827-16832. URL: https://doi.org/10.1103/PhysRevB.61.16827
5. Xiao Dong, Xiuxiu Fang, Yongyong Wang, and Xiaohui Song. "Raman spectra and optical properties of the chalcogen-hyperdoped silicon: a first-principles study". Opt. Express - 26. 2018.- A796-A805.
