ASTM_F_448_-_11.pdf

Designation:F44811Standard Test Method forMeasuring Steady-State Primary Photocurrent1This standard is issued under the fixed designation F448;the number immediately following the designation indicates the year of originaladoption or,in the case of revision,the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon()indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S.Department of Defense.1.Scope1.1 This test method covers the measurement of steady-stateprimary photocurrent,Ipp,generated in semiconductor deviceswhen these devices are exposed to ionizing radiation.Theseprocedures are intended for the measurement of photocurrentsgreater than 109As/Gy(Si or Ge),in cases for which therelaxation time of the device being measured is less than 25%of the pulse width of the ionizing source.The validity of theseprocedures for ionizing dose rates as great as 108Gy(Si or Ge)/shas been established.The procedures may be used for mea-surements at dose rates as great as 1010Gy(Si or Ge)/s;however,extra care must be taken.Above 108Gy/s,thepackage response may dominate the device response for anydevice.Additional precautions are also required when measur-ing photocurrents of 109As/Gy(Si or Ge)or lower.1.2 Setup,calibration,and test circuit evaluation proceduresare also included in this test method.1.3 Because of the variability between device types and inthe requirements of different applications,the dose rate rangeover which any specific test is to be conducted is not given inthis test method but must be specified separately.1.4 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2E668 Practice for Application of Thermoluminescence-Dosimetry(TLD)Systems for Determining AbsorbedDose in Radiation-Hardness Testing of Electronic DevicesF526 Test Method for Using Calorimeters for Total DoseMeasurements in Pulsed Linear Accelerator or FlashX-ray Machines3.Terminology3.1 Definitions:3.1.1 fall time,nthe time required for a signal pulse todrop from 90 to 10%of its steady-state value.3.1.2 photocurrent relaxation time,nthe time required forthe radiation induced photocurrent to decrease to 1/e(0.368)ofits initial value.The relaxation time depends upon therecombination-controlled photocurrent decay in the media,which is often a semiconductor.The relaxation time candepend upon the temperature and the strength of theirradiation/illumination.3.1.3 primary photocurrent,nthe flow of excess chargecarriers across a p-n junction due to ionizing radiation creatingelectron-hole pairs throughout the device.The charges associ-ated with this current are only those produced in the junctiondepletion region and in the bulk semiconductor materialapproximately one diffusion length on either side of thedepletion region(or to the end of the semiconductor material,whichever is shorter).3.1.4 pulse width,nthe time a pulse-amplitude remainsabove 50%of its maximum value.3.1.5 rise time,nthe time required for a signal pulse to risefrom 10 to 90%of its steady-state value.4.Summary of Test Method4.1 In this test method,the test device is irradiated in theprimary electron beam of a linear accelerator.Both the irradia-tion pulse and junction current(Fig.1)are displayed and1This test method is under the jurisdiction of ASTM Committee F01 onElectronics and is the direct responsibility of Subcommittee F01.11 on Nuclear andSpace Radiation Effects.Current edition approved June 1,2011.Published July 2011.Originally approvedin 1975 as F448 75 T.Last previous edition approved in 2005 as F448 99(2005).DOI:10.1520/F0448-11.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 recorded.Placement of a thin,low atomic number(Z13)scattering plate in the beam is recommended to improve beamuniformity;the consequences of the use of a scattering platerelating to interference from secondary electrons are described.The total dose is measured by an auxiliary dosimeter.Thesteady-state values of the dose rate and junction current and therelaxation time of the junction current are determined from thedata trace and total dose.4.2 In special cases,these parameters may be measured at asingle dose rate under one bias condition if the test is designedto generate information for such a narrow applicat