Editorial Radiation Effects in Solar Cells and...

Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2013, Article ID 171753, 3 pageshttp://dx.doi.org/10.1155/2013/171753

EditorialRadiation Effects in Solar Cells and Optoelectronic Devices

Aleksandra Vasic,1 Predrag Osmokrovic,2 Nenad Marjanovic,3 and MomIilo PejoviT4

1 Faculty of Mechanical Engineering, University of Belgrade, Kraljice Marije 16, 11000 Belgrade, Serbia2 Faculty of Electrical Engineering, University of Belgrade, Bulevar kralja Aleksandra 73, 11000 Belgrade, Serbia3 CSEM Centre Suisse d’Electronique et de Microtechnique SAEntwicklungszentrum fur Polytronics, Tramstrasse 99,4132 Muttenz, Switzerland

4 Faculty of Electronic Engineering, University of Nis, Aleksandra Medvedeva 14, 18000 Nis, Serbia

Correspondence should be addressed to Aleksandra Vasic; [email protected]

Received 25 August 2013; Accepted 25 August 2013

Copyright © 2013 Aleksandra Vasic et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

Beside the diversity of the device technologies used fordesigning the solar cells and various optoelectronic devices,there are a variety of radiation environments in which theyare used (natural space and atmospheric, as well as militaryand civil nuclear environments, etc.). Reliability of electricaldevices in a radiation environment is very important, andextensive studies concerning the development of semicon-ductor devices that can operate normally in such conditionshave been seriously undertaken. Possible degradation of theelectrical performance of optoelectronic devices in general,induced by irradiation, means that very strict conditions fortheir application must be predetermined for the worst casescenario. Performance failure in such conditions could havenegative impact on both the financial and environmentalaspects of the device application.

The lifetime of the semiconducting device is restricted bythe degree of radiation damage that the device receives. Thisis an important factor that affects the performance of variousdevices in practical applications. The permanent damage inthe materials is caused by collisions of the incident radiationparticles with the atoms in the crystalline lattice, whichare displaced from their positions. These defects degradethe transport properties of the material and particularly theminority carrier lifetime. This lifetime decrease producesdegradation of the parameters of the device ultimatelyleading to an increase of the noise level. The interactionbetween vacancies, self-interstitials, impurities, and dopantsin the basic material leads to the formation of undesirable

point defects such as recombination and compensator cen-ters which affect performance of the solar cells and otheroptoelectronic devices, especially in space. Introduction ofradiation-induced recombination centers reduces the minor-ity carrier lifetime in the base layer of the p-n junctionincreasing series resistance. After very high doses of radiationseries resistance of the base layer could be so high that mostof the power generated by the device such as solar cell isdissipated by its own internal resistance.

On the other hand, 𝛾 radiation damage is induced by theionization and excitation of the atoms within the junctionspace charge region of a junction device such as solar cell.The presence of impurity atoms that are either added to thebasematerial as donors, or during themanufacturing process,has indicated the possibility that some of the producedelectrons might be trapped by those atoms between thevalence and conduction band. As a consequence, the outputof the optoelectronic device exposed to 𝛾 radiation is alsoreduced. Therefore, from the technological point of view, itis important to study the variations induced by irradiationof semiconductor junction characteristic parameters (idealityfactor, saturation current, etc.) that affect the performanceof the solar cells, photodiodes, phototransistors, and otherphotonic devices.

This special issue reveals recent developments in thevastly undertaken investigations concerning radiation effectsin various optoelectronic devices (solar cells, photodiodes,phototransistors, insulating layers, memories, dosimeters,etc.). Each paper was reviewed by at least two reviewers

2 International Journal of Photoenergy

(mostly three) and presents the most recent breakthroughsin this interesting field.

Many fundamental and practical problems were dis-cussed in the received and accepted papers, ranging fromsolar cells, photodiodes, phototransistors, insulating films,memories, and so forth. Various experimental techniques,numerical analysis, and theoretical discussions were pre-sented in order to reveal current problems, and to offer ade-quate solutions. Behavior of the solar cells, photodiodes, andphotodetectors exposed to gamma and neutron irradiationwas discussed in D. Nikolic et al.’s and B. Simic et al.’s papers,respectively. After thorough investigations, the authors con-cluded that although neutron irradiation in all samplescaused degradation of their structure and deterioration of theoutput characteristics, solar panels have proved to be mostresistant to the effects of neutrons. Also, results obtainedfrom gamma irradiation showed the degradation of the I-V characteristics, but following annealing process improvedthese characteristics. Due to their amplifying action, thephototransistors are the most sensitive to radiation effects.On the other hand, the solar panels are the least sensitive togamma radiation.

Another vast group of electrical devices such as resistorswere considered in the I. Kostic et al.’s paper.The temperaturedependence has been treated without taking the thermalsource into consideration, which means that, in the cosmicradiation conditions, this dependence could be reached bythe collision energy transfer between particle from cosmicradiation and the observed component. Anovel approachwasproposed for thermal testing of the resistors. It was found thatthermography can be used as noncontact method because itgives temperature distribution in more than a couple pointsand because in the short time a set of measurements can bedone.

Radiation effects in insulating films were also investi-gated. In L. Timotijevic et al.’s paper Monte Carlo simulationof proton beameffects on five insulatingmaterials, commonlyencountered in modern day electronic components: silicondioxide, silicon nitride, aluminum nitride, alumina, andpolycarbonate were discussed. It was found that nonionizingenergy loss of high-energy protons is low, and they traversethe films without much atomic displacement. However, forthe lower part of the investigated proton energy range (from10 keV to 1MeV), substantial ionization losses and NIELare to be expected. Ionization and displacement damageproduced by protons could influence the properties of theseinsulators and compromise their reliability within complexstructures and devices.

A newly discovered class of materials, Cooper-pair insu-lators, based on InO

𝑥films, with distinct structural properties

and unique physical mechanism of electrical current conduc-tion were investigated in S. Milosavljevic et al.’s paper. Thestudy suggests that radiation-induced changes in InO

𝑥films

exposed to ion beams could significantly alter their current-voltage characteristics, and that a transition to a metallicstate is possible, due to radiation-induced perturbation ofthe fine-tuned granular structure. Furthermore, incident anddisplaced ions can break up enough Cooper pairs in InO

𝑥

films to cause dissolution of this specific insulating state.

Since Cooper-pair insulators are recently used in resistiverandom-accessmemories, investigation of effects of radiationenvironment on different memory devices is of considerablerelevance. In I. Fetahovic et al.’s paper, different types of com-mercially available memory chips were exposed to indirectionizing radiation by changing radiation dose intensity. Theeffect of direct ionizing radiation on semiconductor memorybehavior has been analyzed by usingMonte Carlo simulationmethod. Obtained results showed that gamma radiationcauses decrease in threshold voltage, being proportional tothe absorbed dose of radiation. Monte Carlo simulations ofradiation interaction with material proved to be significantand can be a good estimation tool in probing semiconductormemory behavior in radiation environment.

Another type of commonly used memories, such asflash memories exposed to radiation, was investigated in B.Cavric et al.’s paper. This topic is up-to-date since the highdegree of components miniaturization integrated into theflash memory causes the extreme sensitivity of this memorytype on the ionizing radiation effects. The effects of ionizingradiation may cause changes in stored data, or even thephysical destruction of the components.The obtained resultsindicate that the sensitivity to gamma rays depends primarilyon the thickness of the dielectric layers of cells, which isabout the same for all tested memories, since they belong tothe same generation of technology. Partial recovery of errorscaused by radiation, in a few weeks at room temperature, wasobserved in all the four types of memory.

One group of semiconducting devices that are by theirfunction always exposed to radiation, dosimeters, were thetopic of M. Pejovic et al.’s paper. Specifically, radiation-sensitive p-channel MOSFETs (also known as RADFETs)have recently been developed for applications in space,nuclear industry research, and radiotherapy, so sensitivity ofp-channel MOSFET to X and gamma irradiation is of greatinterest. Results have shown that the response is greater whenRADFETs are irradiated with X-rays. It was concluded thatthis is a consequence of the dominant influence of photoelec-tric effect in X-ray cases in comparison to Compton’s effectin gamma-ray cases. Another significant conclusion was thata satisfactory response of these RADFETs could be achievedfor lower doses especially in X-ray cases, which would enabletheir efficient application for measuring low doses order ofseveral mGy used in diagnostic and interventional radiology.

All of the presented papers give a substantial insightinto the state of the art concerning this important inter-disciplinary field. Since very comprehensive comparativeanalysis of measurement results has been performed inorder to determine the reliability of optoelectronic devicesin radiation environment, the editorial team expects thatthese paperswould inspire further investigations and possiblebreakthroughs in this important area.

Acknowledgments

We would like to thank all contributing authors, reviewers,and Editorial Board of the International Journal of Pho-toenergy for their support and efforts to make this special

International Journal of Photoenergy 3

issue possible. Also, the support of Safi Hosni, EditorialOffice, Hindawi Publishing Corporation, was invaluable forpreparing this issue, for which we are thankful.

Aleksandra VasicPredrag OsmokrovicNenad MarjanovicMomcilo Pejovic

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