Double Sided Diffusion and Drift of Lithium Ions on Large Volume Silicon Detector Structure

JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.17, NO.5, OCTOBER, 2017 ISSN(Print) 1598-1657 https://doi.org/10.5573/jsts.2017.17.5.591 ISSN(Online) 2233-4866 Double Sided Diffusion and Drift of Lithium Ions on Large Volume Silicon Detector Structure Muminov R. A. 1, Saymbetov A. K. 2, Japashov N. M. 2, Mansurova A. A. 2, Radzhapov S. A. 1, Toshmurodov Yo. K. 1, Mukhametkali B. K. 2, Sissenov N. K. 2, and Kuttybay N. B. 2 Abstract This paper deals with development technology and fabrication of large sized silicon detector structures. New method of double sided diffusion and drift of lithium ions for formation big sized Si (Li) p-i-n structures is offered. It was shown that the compensation time in predetermined volume can be reduced by this method. Also, the basic results of I- V, C V and Energy resolution characteristics of Si (Li) p-i-n structures, for various resistivity were illustrated. Index Terms Diffusion of lithium, drift of lithium ions, p-i-n structure, silicon detector I. INTRODUCTION Development of semiconductor material science has opened broad opportunities in development of semiconductor detectors for nuclear radiation [1]. As the analysis of the world trend the silicon detectors have a special place among them [2], especially the silicon lithium detectors [3]. In comparison with other detectors the silicon lithium detectors have following advantages: high energy resolution; high efficiency of radiation detection; high dynamic power measurement range of the exposure dose; size; high temperature and time stability; Manuscript received Jun. 16, 2016; accepted Sep. 2, 2017 1 Physico- Technical Institute of Academy of Science of Uzbekistan 2 al-farabi Kazakh National University E-mail : asaymbetov@gmail.com It is well known that the Ge-detectors have the highest functional characteristics, but they work under temperature T 77 K, so they need cooling system with liquid nitrogen during the work process [4]. The technologies of production of monocrystals, such as - GaAs, CdTe and CdZnTe, as initial material for detector manufacturing have low efficiency of detection and small energy resolution [5, 6]. Moreover, these materials and technologies of their production are expensive. In Nowadays in the world practice detectors with relative small size are well developed [7-9]. Simultaneously, the development of silicon detectors with big size is necessary [10-12]. In comparison with other semiconductor devices, such as diodes, transistors, thyristors and etc., the structures of detector should correspond with high requirements related to their current, charge, capacitance, nose, spectrometric and time characteristics, also with the sameness of identification of ionizing radiation regardless of its contact with any part of the sensitive area of the detector. In this regard, it is important to study the technological issues caused by effects of big size semiconductor crystals for forming required detector structures with p-n and p-i-n junctions. It is known that to provide thin input window, i.e. thin dead layer, for detector structures a p- n junction of its back side should be sharp and should be located near the surface layer. During the application of inversed bias voltage to the p-i-n structure the basic i- region should have very high resistivity for ensuring its complete depletion. The main physical features, of the processes of diffusion, drift and contact application, appear while forming p-i-n structure on monocrystal silicon of large diameter, and they need to be more

592 MUMINOV R. A. et al : DOUBLE SIDED DIFFUSION AND DRIFT OF LITHIUM IONS ON LARGE VOLUME SILICON investigated and developed to technologically control them. The processes of crystal surface protection (i. e. crystal passivation process), installation in the case and sealing is the most complicated parts of the whole system. Moreover, another challenging technological part is sputter deposition of the gold collector contacts with thickness which allows maximize current transmission and minimize the losses, caused by ionized radiation. The thickness of this gold cover should be uniformly imposed on a big area of detector surface. II. MATERIAL AND METHODS In work [13] we considered the traditional way of Si (Li) p-i-n structure formation. Further in this work we will consider new, double sided diffusion and drift, methods for Si (Li) p-i-n structure fabrication. The dislocation free monocrystal line silicon of p- type, obtained by float-zone method, with diameter 110 mm, thickness 8-10 mm, resistivity ρ = 1000 10000 Ohm*cm and with life time τ 500 μs was taken as an initial material. The diffusion of lithium, to the depth of 300 µm under temperature t=400 0 С during t=4 min, was carried out from the two side of the crystal. After standard chemicotechnological operation the crystals are installed into the drift installation by connecting to electrical circuit. The double sided drift of lithium was carried out under temperature (60 100) 0 С and voltage U=(150 600) V. The drift completion moment is fixed by sharp increase of inversed current. After finishing the compensation process, i.e. joining of two counter fronts of lithium drift, one of the diffusion n-area is grounded off to the depth determined by its degradation during the drift process. The highlighting of i-area is carried out by decorating etchant - HNO 3 : HF=1:1000. The i-area will be accepted as completely highlighted when its contour near to the contour of the circle with diameter equal to the diameter of diffusion area (Fig. 1 and 3). Then, the entire crystal undergoes chemical-processed. The housing of the detector has two rings, between them the detector structure is fixed by the help of compound, such as ELB 10. This compound have very good adhesion characteristics. To the finished structure the Ni and Au contacts is sputtered. On Fig. 4. it is shown the picture of large size Si(Li) detector. Fig. 1. The technological route of manufacturing detector structures. III. RESULTS AND DISCUSSION The silicon- lithium detectors are the basic elements of semiconductor systems for X- ray spectrometry. These detectors represent a structure with p-i-n junctions formed due to the lithium ions diffusion in p-type silicon. Nowadays, the methods, such as one sided diffusion and drift of lithium ions, for formation of Si(Li) p-i-n is widely known [3, 14, 15]. These methods have their disadvantages and technological difficulties. For instance, for formation of high quality p-n or p-i-n structures on large sized plates, with ensuring high plane parallelness of their surfaces, it is necessary to find solutions of several technological problems. These works need a high accuracy, therefore, apart from the traditional method [13], they require more sophisticated special tools to perform a technological process of diffusion and drift of impurity atoms for large sized crystals. To solve this problems we are proposing the method of double sided diffusion and drift of lithium ions for formation of Si(Li) p-i-n structures in large sized crystal. In this method the diffusion of lithium on both front faces to a predetermined depth, sufficient to provide needed compensation of initial acceptor impurity in demanded volume is carried out on pre-treated silicon samples. On Fig. 2 it is shown the diffusion profile of lithium in p- Si crystal, obtained by this method. A slight deviation of lithium diffusion depth from different end surfaces of crystal is associated with non-uniform implementation of Li.

JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.17, NO.5, OCTOBER, 2017 593 Fig. 3. i - region after the drift of lithium ions. Fig. 2. The profile of Li concentration in silicon wafer, after double sided diffusion. Fig. 4. Large size Si(Li) p-i-n detector. 6,0 Current (ma) The basic characteristics of Si(Li) p-i-n X ray detectors of mainly depends on distribution quality of lithium in diffusion area, because during drift process the lithium distribution determines distribution of conductivity of i-area and increases quality of n-i junctions. One of the stages of construction of X ray detectors is compensation of initial semiconductor material (p-si) by lithium ions by the methods of continuous electric field drift, under accelerated mode (high temperature and inverse bias voltage) of diffusion drift processes. In this process the compensation quality is not sufficiently high. Therefore it is necessary to expose the whole volume of the crystal to certain thermal influences. But every thermal influence can cause defects in crystal volume. Consequently, it is necessary to find such technological ways that could supply minimal thermal field in crystal volume. To have such technological way we are developed the method of obtaining Si(Li) p-i-n structure. This method allows reduce compensation time of silicon in big volumes and can eliminate negative effects of prolonged with standing of crystal under high temperature and voltage. On Fig. 1. it is shown the wafers connection diagram for conducting double sided drift (Fig. 1(c)) and a condition of lithium distribution (Fig. 1(d)) after drift process. On Fig. 3 it is shown i- region that was obtained by above mentioned technological method. After contact deposition process (Fig. 4) it was measured electrophysical characteristics of large size Si(Li) detectors. On Fig. 5 and 6. it is shown the inverse branches of I V and C-V characteristics of silicon with resistivity 1 10 kohm. There curve (1) is for silicon with resistivity 1 (3) (2) (1) 4,5 3,0 1,5 0,0 100 200 300 Voltage (V) 400 500 600 Fig. 5. I-V characteristics of Si(Li) p-i-n structures. kohm, curve (2) is for 5 kohm and curve (3) is for 10 kohm. Leakage current also does not have saturation area and highly dependent on inverse bias value. When inverse bias has value 600 V the leakage current has 6 µа. One of the basic characteristics of X- ray detectors is its spectrometric characteristics. We used 226Ra for α radiation and 207Bi for β radiation. The energy resolution of detectors for α-particles is Rα = 46 kev (Eα ~ 7.65 МeV), and for β-particles is Rβ ~ 18 kev (Eβ ~ 1 МeV), under temperature T = 300 K.

594 MUMINOV R. A. et al : DOUBLE SIDED DIFFUSION AND DRIFT OF LITHIUM IONS ON LARGE VOLUME SILICON 40 Capacitance (pf) 30 20 (3) (2) (1) (a) 10 0 100 200 300 400 500 600 Voltage (V) Fig. 6. C-V characteristics of Si(Li) p-i-n structures. (b) 80 E(noise), kev 60 40 20 (3) (2) (1) (c) 0 100 200 300 400 Voltage (V) 500 600 Fig. 8. SPM image of the structure. Fig. 7. Dependence of energy resolution on voltage Si(Li) p-i-n structures. With the help of ionizing radiation sources the division of the channel was defined. Further by the amplitude distribution diagram the value of noise E ins.noise was defined by this expression: ins. noise 0 0 ( ) 2 2 e E = N - E where E ins. noise - installation noise (kev), N 0 number of channel, E noise - noise of detector (kev). On Fig. 7. it is shown the dependence of energy resolution on voltage for crystals with various resistivity, the same crystals that was taken above on Fig. 5 and 6. The dependence of energy resolution from voltage of p-in structures has a long plateau i.e. wide operating voltage range, where the noise level does not change significantly. Another significant parameter of the semiconductor detectors, such as the energetic resolution, the efficiency noise of detection, electro-physical characteristics mainly depend on the characteristics, state and stability of junction surface. So, the investigation of the crystal surface has the specific interest, from the viewpoint of further improvement of the processing and the surface protection. The Scanning Probe Microscope method (SPM) has been used to study the surface of the samples. On the Fig. 8, the 3D image of the structure surface (a,b,c) is shown. IV. CONCLUSION The change of characteristic of lithium distribution in compensated region of Si(Li) p-i-n structures, depending on parameters of initial material and resistivity, attracts extensive attention. In this direction, the new method of Si(Li) p-i-n structure formation for large sized semiconductor detectors of X ray radiation was investigated. In comparison with other existing methods [13], this method has several advantages. First, the double sided diffusion and drift reduces the

JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.17, NO.5, OCTOBER, 2017 595 compensation time of lithium ions. Second, during the double sided drift process all inhomogeneities of initial material is healed. From the obtained electro-physical parameters it can be said that detectors obtained by this method show best characteristics. REFERENCES [1] A. C. Beer et al, Semiconductors for room temperature nuclear detector applications, Academic Press, Vol. 43, 1995. [2] Yu. K. Akimov, "Silicon radiation detectors (Review)," Instruments and Experimental Techniques Vol 50, No.1 pp. 1-28, 2007 [3] S. A. Azimovet, et al. "Silicon-Lithium Nuclear Radiation Detectors." FAN, p. 256, 1981. [4] Th. Stöhlker, et al. "Applications of position sensitive germanium detectors for X-ray spectroscopy of highly charged heavy ions." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Vol.205, pp.210-214, 2003. [5] L. V. Katsoev, et al. "Optimization of the structure of gallium-arsenide-based detectors with taking into account recombination losses." Semiconductors, Vol.43, No.13, pp.1667-1670, 2009. [6] D. S. Stefano, et al. "Progress in the development of CdTe and CdZnTe semiconductor radiation detectors for astrophysical and medical applications." Sensors, Vol.9, No.5, pp.3491-3526, May., 2009. [7] R. A. Muminov, et al. "Developing Si (Li) nuclear radiation detectors by pulsed electric field treatment," Technical Physics Letters Vol.35, No.8, pp.768-769, 2009. [8] R. A. Muminov, et al. "Silicon-lithium telescopic detector in one crystal," Atomic energy, Vol.106, No.2, pp.141-142, 2009. [9] I. Ahmad, et al. "Nuclear spectroscopy with Si PIN diode detectors at room temperature," Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment Vol.299, No.1, pp. 201-204, 1990. [10] R. A. Muminov, et al."special features of formation of high-performance semiconductor detectors based on αsi-si (Li) heterostructures," Instruments and Experimental Techniques, Vol.56, No.1, pp.32-33, 2013. [11] D. Protić, et al. "Large-volume Si (Li) orthogonalstrip detectors for Compton-effect-based instruments," Nuclear Science, IEEE Transactions on, Vol52, No.6, pp.3181-3185, 2005. [12] R. A. Muminov, et al. "Electrophysical characteristics of large-size asi-si(li) detector heterostructures." Semiconductor physics quantum electronics & optoelectronics, Vol.15, No.3, pp.285-287, 2012. [13] A. K. Saymbetov, et al. Development of technology and making of silicon detector structures of large size. Bulletin of National Academy of sciences of the Republic of Kazakhstan Vol.1, No.359, pp.15 18, 2016. [14] J. W. Mayer, et al. "Characteristics of p-i-n Junctions Produced by Ion-Drift Techniques in Silicon," Journal of Applied Physics, Vol.33, No.9, pp.2894-2902, 1962. [15] A. Zamouche, et al. "Investigation of fast diffusing impurities in silicon by a transient ion drift method," Applied physics letters, Vol.66, No.5, pp.631-633, 1995. Muminov Ramizulla was born in 1941. He has 53 years of work experience in the Academy of Sciences of Republic of Uzbekistan, Since 1963 he has been working as a laboratory assistant, research assistant, senior research fellow, deputy director for science of the Physico-Technical Institute of the Academy of Sciences of Uzbekistan, director of the laboratory of the Physico- Technical Institute of Academy of Science of Republic of Uzbekistan, head of the Research laboratory. He was awarded government awards: 1981 "For Labor Distinction", 2006 "Mekhnat Shuhrati", 1992 Awarded the State Prize of the Republic of Uzbekistan. Also was awarded the "Gold Medal" exhibition for the development of semiconductor detectors.

596 MUMINOV R. A. et al : DOUBLE SIDED DIFFUSION AND DRIFT OF LITHIUM IONS ON LARGE VOLUME SILICON Saymbetov Ahmet received the B.S. degree from National University of Uzbekistan, Tashkent, Uzbekistan, in 2005 he received M.S. degree from this institution, From 2006 to 2008 Ph.D. student in Physico-Technical Institute of the Academy of Sciences of Uzbekistan. His PhD thesis was about X- ray detectors. From 2013 he works in Kazakh National University at Department of Solid State Physics and Nonlinear Physics, as a senior lecture, Almaty, Kazakhstan. Nowadays, He continue to work with semiconductor devices and X - ray p- i- n detectors. Nursultan Japashov received the B.S. degree in 2012 and M.S. degree in 2014 from Physics and Technology faculty of al- Farabi Kazakh National University. He is currently pursuing the Ph.D. degree in the Department of Solid State Physics and Nonlinear Physics, Kazakhstan. His interests include semiconductor devices and X-ray detectors. Mansurova Aizhan received the B.S. degree in 2012 and M.S. degree in 2014 from Physics and Technology faculty of al- Farabi Kazakh National University, Almaty, Kazakhstan. Currently, she is assistant in this faculty. Her interests are semiconductor devices, Heterostructural materials and X-ray detectors. Radzhapov Sali was born in 1956. In 1978 he received his B.S. degree. Current, he works at PhysicoTechnical Institute of the Academy of Sciences of Uzbekistan as a Senior Researcher, Tashkent, Uzbekistan. From 2010 he is a Doctor of Physics and Math Science. From 1987 until now he works on developing semiconductor X-ray detectors. Toshmurodov Yorhin was born in 1986. In 2010 he received his M.S. degree from National University of Uzbekistan, Tashkent, Uzbekistan. He has 10 year work experience in Academy of Science of Republic of Uzbekistan. Since 2008 he has been working as a technician, researcher and senior research fellow. His scientific direction is to study the physics of semiconductors and semiconductor devices. Mukhametkali Bauyrzhan received the B.S., M.S., degrees of Physics in the Department of Solid State Physics and Nonlinear Physics, from al- Farabi Kazakh National University. From 2013, he is a lecturer at this department. His interests are semiconductor devices, Heterostructural materials, solar cells. Kuttybay Nurzhigit received the B.S. degree in 2015 and M.S. degree of "Engineering and Technology" in the Department of Solid State Physics and Nonlinear Physics, from alfarabi Kazakh National University, in 2017. Currently, he is an research assistant in the Department of Solid State Physics and Nonlinear Physics. His research interests include semiconductor devices and semiconductor electronics. Sissenov Nursultan received the B.S. degree in 2015 and M.S. degree of "Engineering and Technology" in the Department of Solid State Physics and Nonlinear Physics, from alfarabi Kazakh National University in 2017. Currently, he is an research assistant in the Department of Solid State Physics and Nonlinear Physics. His research interests include semiconductor devices and semiconductor electronics.