ASTM_F_418_-_77_2002.pdf

Designation:F 418 77(Reapproved 2002)Standard Practice forPreparation of Samples of the Constant CompositionRegion of Epitaxial Gallium Arsenide Phosphide for HallEffect Measurements1This standard is issued under the fixed designation F 418;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice covers a procedure to be followed to freethe constant composition region of epitaxially grown galliumarsenide phosphide,GaAs(1x)Px,from the substrate andgraded region on which it was grown in order to measure theelectrical properties of only the constant composition region,which is typically 30 to 100 m thick.It also sets forth twoalternative procedures to be followed to make electrical contactto the specimen.1.2 It is intended that this practice be used in conjunctionwith Test Methods F 76.1.3 The specific parameters set forth in this recommendedpractice are appropriate for GaAs0.62P0.38,but they can beapplied,with changes in etch times,to material with othercompositions.1.4 This practice does not deal with making or interpretingthe Hall measurement on a specimen prepared as describedherein,other than to point out the existence and possible effectsdue to the distribution of the free carriers among the twoconduction band minima.1.5 This practice can also be followed in the preparation ofspecimens of the constant composition region for light absorp-tion measurements or for mass or emission spectrometricanalysis.1.6 This practice becomes increasingly difficult to apply asspecimens become thinner.1.7 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.For hazard state-ment,see Section 9 and 11.9.2.4.2.Referenced Documents2.1 ASTM Standards:2D 1125 Test Methods for Electrical Conductivity and Re-sistivity of WaterF 76 Test Methods for Measuring Resistivity and HallCoefficient and Determining Hall Mobility in Single-Crystal SemiconductorsF 358 Test Method for Wavelength of Peak Photolumines-cence and the Corresponding Composition of GalliumArsenide Phosphide Wafers3.Terminology3.1 Definitions:3.1.1 constant composition regionas applied to epitaxialGaAs(1x)Px,the layer last grown in which the composition isheld fixed at about the desired value of x in mole percentphosphorus;x is typically 0.38.3.1.2 graded regionas applied to epitaxial GaAs(1x)Px,the layer first grown in which the composition is changed fromGaAs to GaAs(1x)Pxduring the growth of the layer.Thepurpose of this layer is to minimize the lattice mismatchbetween the GaAs substrate and the GaAs(1x)Pxlayers.3.1.3 Hall carrier density1/RHe cm3the reciprocal ofthe product of the Hall coefficient and the electronic charge,aquantity related to the charge carrier density.4.Summary of Practice4.1 In this practice(1),3a specimen is cleaved from a fullwafer of GaAs(1x)Px,the substrate is partially removed bymechanical lapping,the remainder of the substrate and the1This practice is under the jurisdiction of ASTM Committee F01 on Electronicsand is the direct responsibility of Subcommittee F01.15 on Compound Semicon-ductors.Current edition approved May 27,1977.Published July 1977.Originallypublished as F 418-75 T.Last previous edition F 418-75 T.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.3The boldface numbers in parentheses refer to the list of references appended tothis practice.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.graded region are removed by chemical lapping,and thespecimen is contacted either by welding or by flip chipmounting.4.2 Complete removal of substrate and graded region isassured either by timed etching in an etchant with a composi-tionally dependent etch rate or by measurement of compositionof the etched surface in accordance with Test Method F 358.4.3 The thickness of the final specimen is measured micro-scopically on a small section cleaved out of the rest of thethinned specimen.5.Significance and Use5.1 The efficiency of light-emitting diodes is known to varywith the carrier density of the starting material.This procedureprovides a technique to prepare specimens in which the Hallcarrier density can be measured in a region typical of that inwhich devices are fabricated.This quantity,which is related tothe carrier density,can be used directly as a quality controlparameter.5.2 Mobility is a function of a number of parameter