Distinction investigation of InGaAs photodetectors cutoff at 2.9 l m

InfraredPhysics&Technology53(2010)

173–176

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InfraredPhysics&Technology

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DistinctioninvestigationofInGaAsphotodetectorscutoffat2.9lm

ChengLia,b,YonggangZhanga,c,*,KaiWanga,b,YiGua,HaosibaiyinLia,YaoYaoLia

a

StateKeyLaboratoryofFunctionalMaterialsforInformatics,ShanghaiInstituteofMicrosystemandInformationTechnology,ChineseAcademyofScience,Shanghai200050,ChinaGraduateSchooloftheChineseAcademyofScience,Beijing100049,Chinac

KeyLaboratoryofInfraredImagingMaterialsandDetectors,ShanghaiInstituteofTechnicalPhysics,ChineseAcademyofSciences,Shanghai200083,China

b

articleinfoabstract

UsingdoubleheterojunctionstructurewithlinearlygradedInxAl1–xAsasbufferlayerandIn0.9Al0.1Asascaplayer,wavelengthextendedIn0.9Ga0.1Asdetectorswithcutoffwavelengthof2.88lmatroomtem-peraturehavebeengrownbyusinggassourcemolecularbeamepitaxy,theircharacteristicshavebeeninvestigatedindetailandcomparedwiththedetectorscutoffat2.4lmwithsimilarstructureaswellascommercialInAsdetectors.TypicalresistanceareaproductR0Aofthedetectorsreaches3.2Xcm2at290K.Measuredpeakdetectivityreaches6.6E9cmHz1/2/Watroomtemperature.

Ó2009ElsevierB.V.Allrightsreserved.

Articlehistory:

Received25August2009

Availableonline1December2009Keywords:

InGaAsphotodetectorsMolecularbeamepitaxyShortwavelengthinfrared

Trapassistedtunnelingcurrent

1.Introduction

ManyeffortshavebeenmadetoextendthecutoffwavelengthoftheInxGa1–xAsphotodetectorsfromabout1.7lm(x=0.53,latticematchedtoInPsubstrate)tothelongerwavelengthsidefortheimportanceoftheshortwaveinfrared(SWIR)bandof1–3lm[1–11],whichexhibitingparticularspectroscopicfeaturesincludingstrongwaterabsorptionbandaround1.4,1.9and2.7lm,aswellasthehighcontrastforearthobservationfromthesatellite[12].However,toourknowledgethelongestcutoffwavelengthofthedetectorsatroomtemperatureisstillaround2.6–2.7lm[2,11],whichcorrespondingtoalatticemismatchofabout2.2%forx$0.85.Furtherextendingofthecutoffwavelengtharisestwoquestions.First,atevenlargerlatticemismatch,aretheperformancesofthedetectorsstillsuitableformanyapplications,ortheperformancesdegradationbecauseoftheepitaxialdefectsstillmoderate?Second,atcertainoperationwavelength(e.g.k$3lm),aretheperformancesoftheInxGa1–xAsdetectors(x>0.85)stillsuperiortothelatticematcheddetectorswithlongercutoffwavelength(e.g.InAs,x=1withcutoffwavelengthof3.6lm)especiallyatroomtemperature[13],orcompetitivetoexistingcommercialdevices[14]?Toanswerthosequestions,inthispaperfurtherextendingofthecutoffwavelengthofInxGa1–xAsdetectorsupto2.9lmisdemonstrated,andtheirperformancesareinvestigatedindetail.Acomprehensivecomparisonofthe

*Correspondingauthor.Address:StateKeyLaboratoryofFunctionalMaterialsforInformatics,ShanghaiInstituteofMicrosystemandInformationTechnology,ChineseAcademyofScience,Shanghai200050,China.Tel.:+862162511070;fax:+862162513510.

E-mailaddress:ygzhang@http://doc.xuehai.net(Y.Zhang).1350-4495/$-seefrontmatterÓ2009ElsevierB.V.Allrightsreserved.doi:10.1016/j.infrared.2009.11.002

detectorfeatureshavebeenmadewithourInxGa1–xAsdetectorscutoffat2.4lmaswellasthecommercialJudsonInAsdetectorscutoffat3.6lm[14].2.Experimentaldetails

Inthisworkthedetectorepi-waferswithstructuresimilarto[9]weregrownbyusingaVGSemiconV80HGSMBEsystem.Inthegrowthof2.9lmdetector(sampleA),thepre-heattreatmentofthesubstratewascarriedoutinthephosphorpressure.Afterthedesorptionofsurfaceoxygen,thesubstratetemperaturewasde-creasedto460°C(measuredbythermalcouple)tostartthegrowthofathinInPbuffer(0.15lminthickness),thenbegunthelinearlygradedN+InxAl1–xAsbufferlayer(2.4lminthickness)wheretheIndiumcompositionxwasgradedfrom0.52(latticematchedtoInP)to0.90atamismatchgradingrateof1.1%/lmusingacorre-latingtemperaturerampingprocedureasdescribedin[9].Afterthat,aIn0.90Ga0.10Asabsorptionlayer(2.0lminthickness)wasgrown,whichwaslightlydopedwithSi,thenendedwithBedopedP+In0.90Al0.10Ascaplayer(0.6lminthickness).Asacomparison,a2.4lmdetectorwafer(sampleB)wheretheIndiumcompositionsofInxAl1–xAsandInxGa1–xAsare0.78wasalsogrownsubsequentlyusingsimilarstructuralandgrowthparameters.Thegrownsam-plesshowshinysurface,butslightcrossripplescanbeclearlyseenalongthe[011]and[01À1]directions,whicharetypicalmor-phologyrelatedtotheexistenceofmismatchdislocations[15],especiallyatlargepositivemismatchedconditions.

Aftergrowth,thewaferswereprocessedintomesa-typedetec-tors.Mesaswithdifferentdiameterswerede nedbyphotolithog-raphyandwetchemicaletchingusingH3PO4/H2O2solution,then

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