CC BY
18
Section 6. Physics
https://doi.org/10.29013/ESR-21-5.6-38-41
Daliev Shakhrukh Kh., leading researcher of Institute of Semiconductor Physics and Microelectronics of National University of Uzbekistan Tashkent, Republic of Uzbekistan E-mail: shakhrukhd@mail.ru Paluanova Anifa D., doctoral student of Institute of Semiconductor Physics and Microelectronics of National University of Uzbekistan Tashkent, Republic of Uzbekistan E-mail: anifa_84@mail.ru
EFFECT OF GADOLINIUM ATOMS ON DEFECT FORMATION IN SILICON DOPED WITH MOLYBDENUM IMPURITIES
Abstract. The processes of defect formation in n-silicon doped with molybdenum, preliminarily doped with gadolinium, have been investigated by the method of DLTS. It was found that the presence of an electrically neutral impurity of gadolinium in the silicon lattice significantly increases the solubility of molybdenum.
It is established that the presence of impurities of rare earth elements, in this case Mo in the volume of silicon, significantly increases the solubility of impurities of refractory elements and at the same time reduces the efficiency of the formation of thermal defects.
Keywords: silicon, doping, diffusion, molybdenum, gadolinium, deep level.
Introduction. It is known that the efficiency of ation even at low concentrations, introduced into
formation and kinetics of annealing of certain de- silicon during growth are in its lattice in electrically
fects in the bulk of silicon depend on the presence of neutral states. In addition, impurities of rare earth el-
various active and inactive uncontrolled impurities, ements, not showing electrical activity, interact with
their content and state in the silicon lattice, other various uncontrolled impurities in silicon [5-6]. It
specially introduced impurities, the presence of sev- follows from the results of numerous studies that
eral impurities at once, and many factors [1-2]. doping of silicon with rare-earth elements signifi-
Among the listed factors, the most interests are cantly changes its properties, increases the stability
the impurities of rare earth elements introduced into of its basic electrophysical parameters to the action
silicon in the process of growing from a melt [3-4]. of ionizing radiation, which is associated with the
It is known that impurities of rare earth elements, presence of metallic inclusions of rare-earth ele-
which are chemically active and prone to complex- ments, which are effective sinks for vacancies. It was
also found that rare earth elements also affect the thermal stability of silicon.
It is known that doping of Si with refractory elements significantly affects the performance of semiconductor devices [7-8], but the data on their electrical activity and interaction with other defects, as well as on the effect on the characteristics of silicon structures, are contradictory. But, despite the huge amount of experimental material, the issues related to the influence of various impurities with uncontrollable impurities and structural defects in silicon and their influence on the parameters of semiconductor devices still remain unclear.
In this regard, the purpose of this work was to study the processes of defect formation in n-silicon doped with molybdenum and the effect on these processes of one of the impurities of rare-earth elements - gadolinium. The studies were carried out using measurements of the spectra of non-stationary capacitive spectroscopy (DLTS).
Experimental technique. Monocrystalline silicon ofn-type conductivity with a specific resistance r = 5 4 4 10 Ohm x cm and an interstitial optically active oxygen content NOopt in the range = 1.2 • 1016 4 7.3 • • 1017cm-3 was used as the samples under study. Silicon was doped with a rare earth element, gadolinium, while growing silicon from a melt.
Then silicon, pre-doped with gadolinium in the process of growing from the melt, was doped with molybdenum by the diffusion method in the temperature range 900-1200 °C for 2 hours from a layer of metallic Mo deposited on the Si surface. To measure the DLTS spectra in the samples under study after doping with molybdenum impurities on n-Si<Mo> plates with <100> orientation and resistivity p — 5 + 20 Ohm-cm, diode structures were fabricated according to a well-known technique [8]. Measurements and processing of spectra are also described in detail in [8; 9]. From the CV characteristics, the dependences 4r = f (Vrev) were deter-
c
mined, which were linear in all studied diodes.
Results and discussion. Analysis of the DLTS spectra shows that the introduction of gadolinium into silicon during the growth of Si from the melt does not lead to the formation of any deep levels in the band gap of silicon, although, according to neutron activation analysis, Gd atoms are present in the bulk of silicon in a sufficiently high concentration (cm-3). This fact indicates that the gadolinium atoms introduced during growth are electrically neutral.
From measurements of the DLTS spectra of Si samples preliminarily doped with Gd, then diffusion-doped with Mo, as well as control samples subjected to heat treatment, the energy spectrum of the formed deep levels was determined. Figure 1 shows the DLTS spectra of n-Si samples doped with molybdenum at 1200 °C followed by rapid cooling (curve 1) and n-Si preliminarily doped with gadolinium in the process of growing silicon from the melt, then additionally doped with molybdenum at 1200 °C (curve 2) and control n-Si (curve 3).
The analysis of the measured DLTS spectra of n-Si <Mo> samples (Fig. 1, curve 1) shows that the diffusion introduction of Mo into Si at 1200 °C followed by rapid cooling leads to the formation of two deep levels in the upper half of the band gap with fixed ionization energies E-0.20 eV and Ec - 0.29 eV. In the lower half of the band gap of these samples, one deep level with an ionization energy Ev+ 0.36 eV was found.
Analysis of the DLTS spectra of the control heat-treated n-Si samples showed that only a level with an ionization energy E-0.20 eV (peak A) is observed in them, and its concentration is much higher than in the samples doped with Mo. Hence, we can conclude that only levels with ionization energies Ec -0.29 eV, Ev + 0.36 eV are associated with molybdenum atoms in n-Si <Mo>, and the level E-0.20 eV is probably a defect of heat treatment.
Comparison of curves 1 and 2 in the DLTS spectra of n-Si<Mo> samples (Fig. 1) shows that the presence of rare earth elements impurity in the silicon lattice, in this case Gd, leads to the transformation of the DLTS spectra: the concentrations of levels associated with
molybdenum atoms increase by 1,5 times in n- Si<Gd, thermal defects, significantly decreases in the presence Mo> compared to n-Si<Mo>. It should be noted that of gadolinium atoms, that is, the atoms of rare-earth the concentration of deep level E -0.20 eV, caused by elements prevent the formation of thermal defects.
1.0
0,5
"AU, relative units A ' ■ . 2 i \
; I J , 3/ \ l 1 »
M ;/\\
/A\ it V;
j \U \
100 150 200 250 T. K
vT
< ; 2V
c -AU, relative units
0.5
1.0
Figure 1. Typical DLTS spectra of samples n-Si <Mo> (1) and n-Si < Gd, Mo> (2),T , 0C: 1200, n-Si (3) - control sample
As can be seen from the analysis of this figure, the presence of gadolinium atoms in the bulk of silicon increases the solubility of molybdenum atoms, while the concentration of E -0.20 eV levels associ-
c
ated with thermal defects decreases.
Conclusion. Thus, it can be concluded that the presence of rare-earth impurities in the bulk of sili-
con significantly increases the solubility of impurities of refractory elements, in this case, Mo in silicon, and simultaneously reduces the efficiency of formation of thermal defects. This indicates that rare-earth impurities in Si act as internal getters for various defects in the bulk of silicon, as well as for uncontrolled technological impurities.
References:
1. Bourgouin J., Lanno M. Point defects in semiconductors. Theory. - M., Mir, 1984. - 264 p.
2. Zolotukhin I. V., Kalinin Yu. E., Stoney O. V. New directions of physical materials science. Voronezh: Ed. Voronezh State University, 2000. - 360 p.
3. Shindich V. L. Investigation of the processes of radiation defect formation in Si doped with REE. Abstract of Candidate Dissertation, - Kiev, 1982. - 17 p.
4. Castaldini A., Cavallini A., Fraboni B., Pizzini S. On the role of extended defects in the transport properties of Er-doped silicon. Phil. Magazine B, 2000. - Vol. 80. - P. 571-577.
5. Lazaruk S. K., Wise A. V., Ivanyukovich A. V., Leshok A. A., Unuchek D. N., Labunov V. A. Photoluminescence of Erbium-Doped Alumina Films with Embedded Silicon Nanoparticles. FTP, 2005. - T. 39. - V. 8. - P. 927-930.
6. EmtsevV. V., Emtsev V. V. (Jr.), Poloskin D. S., Sobolev N. A., Shek E. I., Mikhel J., Kimerling L. S. Impurity centers in silicon doped with rare-earth impurities dysprosium, holmium, erbium, and ytterbium. FTP, 1999. - T. 33. - Issue. 6. - P. 649-651.
7. Daliev Sh. Kh., Vlasov S. I. Nonequilibrium processes in MIS-structures on the basis of silicon, doped with hafnium. Journal of Scientific and Engineering Research (JSAER), 2017. - 4(4). - P. 11-13.
8. Daliev Sh. Kh., Paluanova A. D. Influence of y-radiation properties of wolframium levels in silicon. Science and world. 2018. - No. 10(62). - Vol. I. - P. 28-31.
9. Daliev Sh. Kh. Influence of Zr, Ti and Hf impurities on the electrophysical properties of silicon structures. Abstract of doctoral dissertation. - Tashkent, 2017. - 47 p.
