The Effect of Gamma Ray Source Nucl.137/LB905 Nom. Activity 3.7 MBq on a Photodiodes

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1 Journal of Applied and Industrial Sciences, 2013, 1 (3): 23-29, ISSN: (PRINT), ISSN: (ONLINE) 23 Research Article The Effect of Gamma Ray Source Nucl.137/LB905 Nom. Activity 3.7 MBq on a Photodiodes 1* Sawsan Ahmed Elhouri Ahmed, 2 Mubarak Dirar Abd-Alla 1 University of Bahri-College of Applied & Industrial Science, Dept of Physics. 2 Sudan University of Science & Technology-College of Science, Dept of Physics (Received: June 9, 2013; Accepted: August 14, 2013) Abstract This research aim to study the influence of gamma radiation on the structure of the photodiode and the current of the photodiode. Photodiodes have been irradiated at different distances to a dose of 3.7 MBq. Current and voltage has been measured several times at different distances during and after exposure and were presented in graphs. These diagrams show the influence of gamma radiation on photodiodes. The results show that gamma irradiation reduces the current of a photodiode. After exposure photodiodes have been recovered from the effects of radiation and Changes in photodiode current have been observed. Index Terms Gamma radiation; Photodiodes; Exposure; Compton Effect; Photocurrent ; Electron-hole pair; Minority carrier; Recombination centers P I. INTRODUCTION ossibilities of application of photo detectors based on photodiodes are very high, Primarily because of their relatively low cost, small size and high speed response (among the Highest in comparison to all other types of detectors). However, like all other types of photo detectors, photodiodes have certain limitations and disadvantages, too [1]. If the photodiode is Powered by the constant voltage, its response (current) is practically identical to the technical information provided by the manufacturer even if it has previously been subjected to the Radiation (in that case the current is only a bit weaker). On the other hand, if the voltage is not constant and the photodiode is located in the areas with strong gamma radiation, then its Response varies from the one that is expected. Therefore, the improvement of the electrical Properties of photo detectors based on photodiodes is very important. The aim of this study was to research the behavior of photodiodes in no ideal conditions (gamma radiation) [2]. When gamma rays interact with materials, they create two effects, the first is ionized (photoelectric effect, Compton scattering, and pair production). The second is atomic displacement. The radiation affects the gap between the conduction band and valence band in two ways also. First; *Corresponding author E. mail: sawsan.ahmed110@gmail.com generation and recombination of electron-hole pairs degrade the minority carrier lifetime. Second; the trapping and compensation effects change the majority carrier density and decrease the carrier mobility. The results show that under the influence of these effects the reduction of photocurrent is significant [3].Optoelectronic devices in which the active elements are semiconductors are frequently sensitive to radiation because the absorption or generation of light in a solid medium is influenced by the defect structure of that medium [1, 2, 3, 4, and 5]. For this reason, extensive research has been undertaken to develop semiconductor devices that can operate in conditions of increased radiation. Typical representatives of the semiconductors used as photo detectors are photodiodes. We explained in this study the effect of gamma radiation on both voltage and current of a photodiode. As well known gamma radiation damage the structure of the photodiode. Unfortunately this damage is irreversible; as a result the current decreases after After exposure, when the radiation comes to partial recovery (relaxation) semiconductors are somehow re-established in recognizing percentage their properties. In this work current of photodiodes affected by gamma radiation is recorded [6]. Theoretical Analysis When gamma rays interact with the material, the primary effects, depending on the Energy of radiation, are: photoelectric effect and Compton Effect [7, 8 and 9], which leads to the creation of electron-hole pairs and the creation of recombination centers. Creation of recombination centers in the energy gap in the interface areas is particularly important because their density may even be equal to the density of surface atoms. Numbers of recombination centers are proportional to the energy, i.e. dose radiation. These recombination centers will attract the free electrons, i.e. reduce minority carrier lifetime. Because of that the current is smaller after irradiation. Of course, the higher dose of radiation should create more recombination centers and thus smaller current. Photodiodes are diodes which are sensitive to light photon. The diode current I in the presence of light is sensitive to saturation current ( I 0 ), depletion voltage (V 0 ), voltage (V) and photo current (I p )

2 Journal of Applied and Industrial Sciences, 2013, 1 (3): 23-29, ISSN: (PRINT), ISSN: (ONLINE) 24 Where A is constant II. MATERIALS AND METHODS We have studied the influence of gamma radiation on the photodiode current. The settlement of the experiment was as follows: Apparatus: - Gamma ray Nucl.137/LB 905 Nom. Activity 3.7 MBq -Sealed lead acid rechargeable battery SUNCA, 9V, 4.5Ah - Six Photodiodes (R = Ω) - Potentiometer -Digital multimeter, voltage range: 200mV V; Current range: 200mV---200μA. - Connecting wires. Method: - The photo-diode is connected to the DC and the potentiometer and across the circuit voltmeter and ammeter were connected. Then the photo-diode is placed in front of the gamma ray at different distances (2,3,4,5 cm) The sliding contact in the potentiometer enables the voltage to be varied from zero to the maximum obtainable from the supply. Reading of the voltage and current were taken through three different stages. First before the exposure of the photo-diode to the gamma ray. Secondly during the exposure and at last away from the. III. RESULTS AND DISCUSSION The following tables show the relation between current (I) and Voltage (V) for photodiode before exposure, during exposure and after exposure to gamma radiation; for four photodiode speeches (P2, S27, TFM5380 and 0317A-1015) Result e = 1.60 X C ; K = 1.380X10-23 J/molecule.K ; T = 303 K. Before the photo-diode is exposed to the gamma ray. Table (1) Relation between (I) and (V) for (P2) before exposure Distance of the photo-diode from the = 2 cm Table (2) Relation between (I) and (V) for (P2) Fig (1): Relation between (I) and (V) for (P2) before Exposure Fig (2): Relation between (I) and (V) for (P2) during

3 Journal of Applied and Industrial Sciences, 2013, 1 (3): 23-29, ISSN: (PRINT), ISSN: (ONLINE) 25 the distance was 2 cm Table (3) Relation between ( I) and( V) for (P2) Fig (4): Relation between (I) and (V) for (S27) during the distance was 3 cm Table (5) Relation between (I) and (V) for (S27) Fig (3): Relation between (I) and V for (P2) after Distance of the photo-diode from the = 3 cm Table (4) Relation between (I) and (V) for (S27) Fig (5): Relation between (I) and (V) for (S27) after

4 Journal of Applied and Industrial Sciences, 2013, 1 (3): 23-29, ISSN: (PRINT), ISSN: (ONLINE) 26 Distance of the photo-diode from the = 4 cm Table (6) Relation between (I) and (V) for (TFM5380) Fig (7): Relation between (I) and (V) for (TFM5380) after Distance of the photo-diode from the = 5 cm Fig (6): Relation between (I) and (V) for (TFM5380) during Table (8) Relation between (I) and (V) for( 037A-1015) the distance was 4 cm Table (7) Relation between (I) and (V) for (TFM5380) Fig (8): Relation between (I) and (V) for (037A-1015) during

5 Journal of Applied and Industrial Sciences, 2013, 1 (3): 23-29, ISSN: (PRINT), ISSN: (ONLINE) 27 the distance was 5 cm Table (9) Relation between (I) and (V) for (037A-1015) Fig (3) P2 After exposure, distance = 2 cm Fig (9): Relation between (I) and (V) for (037A-1015) after Fig (4) S 27 Photo diode during exposure, distance = 3 cm Fig (2) P2 Photo diode during exposure, distance = 2 cm Fig (5) S27 After exposure, distance = 3 cm

6 Journal of Applied and Industrial Sciences, 2013, 1 (3): 23-29, ISSN: (PRINT), ISSN: (ONLINE) 28 Fig (6) TFM 380 Photo diode during exposure, distance = 4 cm Fig (9) 037A-1015 after exposure, distance = 5 cm Discussion In view of Figs (2, 4, 6, and 8) it is clear that the current of the photodiode increase due the decrease of photocurrent (I p ), as shown by equation (1) where the photocurrent (I). When the gamma ray irradiates the diode the diode current increases by two mechanisms. The first mechanism results from the effect of gamma photons, in taking more electrons form the valence to the conduction band. The rest of energy of gamma photons is gained by electrons in the form of kinetic energy, which in turn increases the diode current[10,11] (2) (3) Fig (7) TFM5380 After exposure, distance = 4 cm Fig (8) 037A-1015 Photo diode during exposure, distance = 5 cm The second mechanism is the decrease of photocurrent which observed in Fig [(3)-table (3)] for diode (P2). According to Fig [(3)-table (3)] the photocurrent decreases from (0.02A) before exposure to almost (zero) after The same hold for the rest of the samples( S27,TFM5380 and 037A- 1015), where Fig [(5)-table(5)] for (S27) shows a decrease from( 0.24A to 0.16 A) to almost (zero), while a decrease for (TFM538) is from (0.09A to 0.05A) as indicated by Fig [(7)- table(7)],and Fig [(9)-table(9)] the current decreases form( 0.15 to 0.14 A) to almost (zero) repeatedly. The decrease of (I P ) is closely related to what happen in depletion layer. The incidence of gamma rays on negative ions in the (p) side causes electrons to be ejected by the photoelectric effect out of the diode. This decreases the depletion voltage (V 0 ) which derive photo current (I P ). The free electrons on the (p) side are ejected outside the diode as well, which decreases free carriers that contribute to (I p ), thus the increase of (I) is due to injection current.

7 Journal of Applied and Industrial Sciences, 2013, 1 (3): 23-29, ISSN: (PRINT), ISSN: (ONLINE) 29 (4) And decreases of photocurrent (I p ), where exposure of photodiodes to gamma rays decreases their photocurrent. Thus the performance and efficiency of solar cells made from silicon and photodiode decreases. Thus it is preferable to protect these devices from the gamma rays. The injection current (I i ) does the longer increases, but the photocurrent (I p ) still decreases due to decreases of electron free carriers and decrease of depletion voltage (V 0 ) by photo electric effect thus[12,13] I (increases) = (decrease) (6) Thus the current increases also after exposure but by fewer rates. IV. CONCLUSION Observing these diagrams it is obvious that some photodiodes have similar diagrams. Table (3, 5, 7, and 9) shows that gamma irradiation influenced the structure of photodiodes resulting in the decrease of photocurrent. After recovery the photodiodes (after exposure) resulted in the increase of the diode current. Irradiation lets to larger structure damages and smaller current. The decrease of current is caused by the creation of recombination centers in the state of the material. Also, we can say during the interactions with photodiodes gamma rays Give a large amount of energy to the electrons [14, 15]. Under the influence of that energy some of valence electrons will come out of atoms and become free thus creating recombination centers. Minority carriers would later recombinant in these recombination centers, which will result in the current reduction. Some charge carriers will recombinant in these recombination centers and that will decrease the minority carrier lifetime.during the period of recovery the concentration of the recombination centers should be partially reduced due to the diffusion motion of free electrons and their recombination. Therefore, the current should increase. The permanent damage the photodiodes is caused by collisions of the incident radiation particles with atoms in the crystalline lattice, which are displaced from their positions. These defects degrade the transport properties of the material and particularly the minority carrier lifetime. Spontaneous fluctuations in the rates of generation, recombination and incidence of charge carriers cause the fluctuations in the density of charge carriers, which produces generation recombination noise [16]. Diffusion noise also arises as a result of localized fluctuations in the density of charge carriers but also due to fluctuations in the rate of diffusion. In any case, each of these noises affects the density of free charge carriers and thus the level of current of the photodiode. Another reason for the drastic decrease of photodiode current could be the amount of energy introduced into the material. So we get the following conclusion; the REFERENCES [1] W.W. Moses, S. E. Derenzo, C. L. 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