Alexandr V. Gradoboev, Doctor of Technical Science, professor Influence of irradiation by 60Co gamma-quanta on reliability of IR-LEDs based on AlGaAs heterostructures Alexandr V. Gradoboev, Doctor of Technical Science, professor

Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru Introduction IR-LEDs is used in various microelectronic devices operated in space conditions and at nuclear power plants. Operation conditions of LEDs require knowledge of their durability and reliability with complex and combined influence of radiation resistance and long operating time1. Figure 1 Photo of IR-LEDs based on AlGaAs heterostructures 1 A.V. Gradoboev and A.P. Surzhikov, The Radiation Resistance Microwave Devices Based on Gallium Arsenide (Tomsk Polytechnic University, Tomsk, 2005), p. 277. Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru

A. V. Gradoboev, +79138668405, gradoboev1@mail.ru Urgency Reliability – accelerated tests: force the aging processes; reduce the length of time required for the information; accelerating factor is temperature. Radiation resistance – simulated equipment. Well-known methods of LED reliability assessment: time-consuming; requiring for significant financial expenditures; demand special equipment. Obtaining information of reliability during development devices is difficult. A. V. Gradoboev, +79138668405, gradoboev1@mail.ru

Purpose and objects of research Purpose is research the influence of preliminary irradiation by 60Co gamma-quanta on operating ability of IR-LEDs. Оbjects of investigation were serial LEDs manufac-tured on the basis of dual AlGaAs heterostructures with 5 μm active layer grown on the monocrystalline n-GaAs wafer by means of liquid epitaxy. Figure 2 Фотография СД ИК-диапазона на основе гетероструктур AlGaAs Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru; Anastasiia V. Simonova, +79234020262, ainakim297@yandex.ru; Ksenia N. Orlova, +79502775499, kemsur@rambler.ru.

Ksenia N. Orlova, +79502775499, kemsur@rambler.ru. Research methods Operating parameters of LEDs in continuous power mode: supply voltage Uop < 2 В; maximum radiant wavelength Forward operating current  = 0.82 – 0.9 мкм. Iop = 50 мА; Parameters of step-by-step tests: Number of LEDs in each batcn – 20 items, ambient temperature T0 = 65ºС; increment step of current Istep = 50 мА; operating current of the first step I1 = 50 мА; duration of each stage t = 24 ч. Figure 3 Типовая конструкция светодиода: 1 – кристалл, 2 – линза и корпус из оптического компаунда, 3 – выводы питания Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru; Anastasiia V. Simonova, +79234020262, ainakim297@yandex.ru; Ksenia N. Orlova, +79502775499, kemsur@rambler.ru.

Ksenia N. Orlova, +79502775499, kemsur@rambler.ru. Research methods LEDs Second batch (LED-2) First batch (LED-1) Third batch (LED-3) LED-1 – step-by-step tests without preliminary irradiation; LED-2 – with preliminary irradiation with dose equaled to Dγ1 = 5∙104 Gy; LED-3 – with preliminary irradiation with dose equaled to Dγ2 = 2∙106 Gy. Preliminary irradiation was led to 60Co gamma-quanta in passive power mode of LEDs. Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru; Anastasiia V. Simonova, +79234020262, ainakim297@yandex.ru; Ksenia N. Orlova, +79502775499, kemsur@rambler.ru.

Measurement of LEDs parameters volt-ampere (V-I) characteristics; watt-ampere (W-I) ball characteristics. Equipment «Poli-500»: forward voltage: 0 – 5 V; forward current: 1 – 500 мА; step: at least 1 мА; error of forward current setting from given level – ± 2%; error of forward voltage measurement – ± 2%; error of emissive power measurement of LEDs doesn’t exceed 5%. Figure 4 Equipment for measurement of LEDs parameters “Poli-500”. Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru; Anastasiia V. Simonova, +79234020262, ainakim297@yandex.ru; Ksenia N. Orlova, +79502775499, kemsur@rambler.ru.

Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru Equipment «Explorer» Isotopic continuous source of gamma radiation; emitter isotope – 60Со; dose rate ~ 1 Gy/s; avegate gamma-quanta energy – 1,25 МэВ; certified volume – 3 litres; irradiation time – absorbed radiation dose. Figure 5 Gamma-installation «Explorer» Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru

Initial characteristics of LEDs Figure 6 V-I characteristic of initial LEDs: 1 –before connection of dislocations, 2 – with connection of dislocations, 3 – demonstration of ohmic contacts resistance, lines – areas V-I characteristic described power function of supply voltage. Figure 7 Equivalent circuit of LED: Rc1, Rc2 – ohmic contacts resistance, p-n-LED – p-n-junction (active layer) of LED, p-n-Disl –dislocation with derived connection to p-n-junction of LED. Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru

Initial characteristics of LEDs mid-level electron injection (field I); high level electron injection in active layer of LED (field II); boundary current separated fields I and II; the dependence incline of field I is less than the dependence incline of field II; border between fields I and II doesn’t coincide with border of demonstration dependence 1 and dependence 2 in the V-I characteristics (fig. 5); W-I characteristics describe light-technical preporties of p-n-junction LEDs. Figure 8 W-I characteristics of LEDs Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru

Changes of LED-1 characteristics during step-by-step tests Figure 9 Change of emissive power for LED-1 (left) batch depending on step number at operating current equaled 50 mA and LED-12 and LED-2 2 (right) depending on irradiation dose by gamma-quanta: 1 – first stage of emissive power fall, 2 – second stage of emissive power drop. 2 Gradoboev A.V., Sednev V.V. Izvestiya vyzov. Physics. – 2014, т.57, № 10/3. – Р. 20. Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru

Influence of preliminary irradiation on LED characteristics Figure 10 W-I characteristics for LED-2 (left) and LED-3 (right) batches: 1 – initials, 2 – after preliminary irradiation; a – low level electron injection field; I, b – mid-level electron injection field; II, c – high level electron injection field in active layer of LED. Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru

Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru Influence of preliminary irradiation on the long operating time of LEDs Figure 11 W-I­ characteristics for LED-2 (left) and LED-3 (right) batches: 1 – initials, 2 – after preliminary irradiation, 3 – after first step of tests, 4 – before development of catastrophic failures; a – low level electron injection field; I, b – mid-level electron injection field; II, c – high level electron injection field in active layer of LED. Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru

Changes of emissive power for LED-2 at operating current equaled 50 mA Distinctive subgroups: - A (10% от СД-2), - B (30% от СД-2), - С (30% от СД-2), - D (25% от СД-2). Incline of stage 1 ~ 1/η, here η – efficiency coefficient. Efficiency of “memory effect”3,4. Figure 12 Change of emissive power during operating time for LED-2 batch: 1 – first stage of emissive power fall, 2 – second stage of emissive power drop. 3 Gradoboev A.V., Sendev V.V. IOP Conf. Series: Materials Science and Engineering 81 (2015) 4 Gradoboev A.V. 24th Int. Crimean Conf. “Microwave & Telecom. Tech.” (CriMiCo’2014) Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru

Изменение мощности излучения СД-3 при рабочем токе 50 мА Изменение мощности излучения СД-3 при рабочем токе 50 мА Rise of emissive power during step-by- step tests; Distinctive subgroups: 1 – Т11 =(348±2) К; Т12 = (362±2) К; 2 – Т21 = (348±2) К; Т22 = (352±2) К; Т23 = (370±2) К; 3 – Т31 = (352±2) К ; Т321 = (367±2) К. Active layer temperature of LEDs: here RT – thermal resistance. Figure 13 Change of emissive power during operating time for LED-3 batch depending on step number Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru

Сomparison of emissive power changes Figure 14 Comparison of emissive power changes during step-by-step tests Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru

Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru Conclusion 1. Investigated LEDs had s-shaped V-I characteristics because of derived connection of p-n-junction dislocations to p-n-junction active layer of LED. 2. In the result of investigation we have established the limit step of tests is determined by catastrophic failures due to mechanical destruction of LED package. 3. We have determined emissive power decrease of LED during operating time have two stage. On the first stage decrease of LED emissive power is due to rearrangement of original defect structure. On the second stage emissive power goes down as the result of inducing new structural defects. Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru

Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru Conclusion 4. We have shown identical multistage mechanism of emissive power drop are observed during both operating time and influence of ionizing radiation. 5. Preliminary irradiation by 60Co gamma-quanta in the field of radiation- stumulated rearrangement of initial defect structure allows to improve reliability and operation life. Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru

Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru Conclusion 6. Preliminary irradiation by 60Co gamma-quanta in the field of merely radiation defect effect results in rise of emissive power of LEDs during operating time and it allow to improve reliability and operation life more appreciably. 7. We have revealed “memory effect” of radiation influence becomes apparent during operating time of LEDs. Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru

Thank you for attention Alexandr V. Gradoboev, +79138668405, gradoboev1@mail.ru