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Section 7. Physics
Aminov Nusrat, Faculty of Electronics and Automatics, State Technical University, Tashkent, Usbekistan
Sultanova Yulduz, Faculty of Electronics and Automatics, State Technical University, Tashkent, Usbekistan Khujaniyazova Azizakhon, Faculty of Electronics and Automatics, State Technical University, Tashkent, Usbekistan
Mavlyanov Abdulaziz, State Technical University - affiliated Uzbek-Japan Innovation
Center of Youth E-mail: [email protected]
PHOTOCONDUCTIVITY SPECTRUM OF SILICON DOPED BY MANGANESE AND SULFUR
Abstract. The spectral dependences curve of the photoconductivity of manganese and sulfur-doped silicon Si <MnS> is presented. For experiments the initial silicon sample was single-crystalline boron-doped silicon with p = 1 O cm. Over the entire energy range of hv = 0.226 ^ 1.28 eV in the Si <MnS> sample, the current increases by three orders of magnitude. From the analysis of the curve, the levels E1 = 0.226 eV and E2 = 0.86 eV were detected.
Keywords: single-crystalline silicon, energy of ionization, photoconductivity, dark current, resistivity.
1. Introduction O cm samples launches at hv = 0.3 eV and was char-
Photoconductivity of sulphur-doped silicon acterized by a small maximum at hv = 0,38 eV. In the was studied in [1, P. 262-266]. As authors report i-type samples with p = 105 O cm, the dark spectrum in the paper, the original p-type silicon wafers had was monotonic. In these samples, the dark photocon-
p = 20 O cm resistivity. After doping with sulfur at ductivity grew monotonically starting at hv > 0.5 eV. temperature of 1200 °C, the initial p-type silicon wafer 2. Main Part
turned into an i-type one with p = 105 O cm resistivity Sulphur in silicon is believed to manifest large va-
and an n-type with p = 103 O cm resistivity, respectively. riety of ionization energies E, determined by various
The photoconductivity measurements were performed authors as shown in (Table 1.) Such variety of ioniza-
an IKS-21-type infrared (iR)-spectrometer at temper- tion energy values and the occurrence of the ioniza-
ature of 77K. The dark photoconductivity of p = 103 tion energy band in the range of hv = 0,28^0,38 eV,
the authors in [1; P. 262-266] are inclined to explain spaced singly-charged atoms and thus the ioniza-
by the fact that sulphur in silicon is a relatively small tion energy of electrons is determined not only be
single-charged donor, and the formation of deeper potential of ionization of isolated sulphur atom, but
impurity levels may be due to the fact that sulphur also by the Coulomb force of the ions present in the
comparatively easily forms associations of closely association.
Table 1.- ionization energy levels E of sulfur determined by different authors by using different techniques
E1 E2 Centers and bands Technique Authors
E= 0.18 eV E= 0.37eV R.O. Carlson, R. N. Hall et al. J. Phys. Chem. Sol., 8,81 (1959)
E= 0.1 eV E= 0.61eV Optical spectroscopy W.E. Krag, H.J. Zeyger et al. J. Phys. Soc Japan (Suppl), 21, 230 (1966)
E= 0.1 eV E= 0.19eV Temperature dependence of the Hall coefficient D.L. Camphausen et al.Am. Phys. Soc, 13, 406 (1968)
E= 0.275 eV E= 0.53eV Photocapaci-tance C.T. Sah, L. L. Rosier at al. Appl. Phys let,15,316 (1969) C. T. Sah, L. L. Rosier at al. Sol. St. Electron.,14, 41 (1971)
E= 0.18B E= 0.37eV Band E=0,28^0,38eV E = 0.5eV Photoconductivity and IR-quenching A.A. Lebedev, A. T. Mamadalimov and N. A. Sultanov, FTP, 5, 22 (1971)
E= 0.26B E= 0.48eV Encyclopedic data M.K. Bakhadirhanov and I. B. Ortikov, Encyclopedia/Semiconductor materials.: TasGTU, 2006.- p.132-135
S1 = 0.318 eV, S+1= 0.614 eV S2==0.188 h S+2=0.37 eV Sy=0.06-0.1 eV S2-> SX Temperature dependence of the Hall coefficient Yu. Astrov and et al. FTP, 2013, vol. 47, no. 2. p.211-215.
3 Experimental
We carried out doping with sulfur and manganese by using diffusion doping technique in vacuumed (10-4 bar) and sealed quartz ampoules at a temperature of 1260 °C and 1200 °C, respectively, for a duration sufficient for uniform doping. The initial samples were Si wafers doped with boron, with an initial specific resistance in the range of p = 1 Q cm. After doping with Mn and S, the initial
silicon remained of p-type, but the resistivity increased to p = 2.4 • 104 Q cm.
In order to study the photoconductivity curve of the silicon sample doped with Mn and S, the authors had performed measurements at IKS-21 spectrometer equipped with a cryostat, which allows one to study photoconductivity in a wide temperature range (T = 77 ^ 350 K). To study the impurity photoconductivity only, a double filter of polished
monocrystalline silicon wafer was used, which was installed before the cryostat window after the infrared light emitter of IKS-21.
The (Fig. 1) shows the spectral dependence of photoconductivity of Si <Mn, S> samples (initial silicon doped with boron -1 with p = 1 Q cm) in the dark and under background light (source is a conventional incandescent lamp with a power of 2 V). As is clear from (Fig. 1), the photoconductivity in silicon samples doped with Mn and S in the dark launches at hv ~ 0.226 eV. In the range of hv = 0.226-0.42 eV, with an increase in the photon energy, the photoconductivity increases continuously and then the saturation region of the photocurrent gradually begins to manifest itself. At hv = 0.42 eV, a sharp decrease
in photoconductivity occurs, and a further increase in the photon energy leads to a noticeable decrease in photoconductivity value with a relatively deep minimum at hv ~ 0.45-0.46 eV. The non-monotonous photoconductivity in the region hv = 0.226-0.46 eV, apparently, is due to the fact that there is a non-monotonous dependence of the ionization cross section, which is given in the theory of G. Lukovsky [2; P. 299-302].
In [1, P. 262-266] for the silicon samples doped with sulfur, the dark photoconductivity in samples with p = 103 Q cm begins at hv = 0,3 eV, whereas in [3: P.140-142] in samples of silicon doped with manganese with resistivity p = 7 • 103 Q cm, the photo-response begins at hv = 0.4 eV.
Figure 1. Spectral curve of photoconductivity of sample Si<MnS> (initial wafer silicon doped with boron-1 with p = 1 Qcm) in dark and at constant background light at Т = 77К
4. Conclusion
Based on the analysis of literature data and the results of experiments photoconductivity, it can be argued that Si <MnS> samples manifest impurity photoconductivity in the wavelength range A = 1.4-5.4 ^m.
Overall, over the entire energy range of hv = 0.226 - 1.28 eV in the Si <MnS> sample, the current increases by three orders of magnitude. From the analysis of the curve, the levels E1 = 0.226 eV and E2 = 0.86 eV were detected, and the second level should most likely be measured from the bottom of
the conduction band and might represent either a associated with transitions between impurities of deep donor level (which is unlikely) or a local level manganese and sulfur.
References:
1. Lebedev A. A., Mamadalimov A. A. and Mahkamov Sh. "Research ofphotoconductivity and IR quenching in Si<S> A. A. Lebedev Лебедев А. А., Мамадалимов А., Махкамов Ш. Исследование ФП и ИК гашение в Si<S> // ФТП. 1974.- № 8.- С. 262-266." Physics and Technology of Semiconductors,-No. 8. 1974.- P. 262-266.
2. Lucovsky G. V. "On the photoinization of deep impurity centers in semiconductors". Sol. St. Commune-No. 3. 1965.- P. 299-302.
3. Bakhadirkhanov M. K. and Isamov S. B. "IR photodetectors that operate in the presence of background light, Бахадырханов М. К., Исамов С. Б. ИК фотоприемники, работающие при наличии фонового освещения. ЖТФ, 2016. - том 86. - Вып. 3. - C. 140-142." Journal of Technical Physics, 2016.- том 86. - Вып. 3.- P. 140-142.
