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Page 1: 1.3 μm quantum-dot micro-disk lasers directly grown on (001) … · 2019-12-13 · 1.3 μm quantum-dot micro-disk lasers directly grown on (001) silicon Alan Y. Liu1*, Yating Wan2,

1.3μmquantum-dotmicro-disklasersdirectlygrownon(001)silicon

AlanY.Liu1*,YatingWan2,QiangLi2,EvelynL.Hu3,KeiMayLau2,ArthurC.Gossard1,JohnE.Bowers11:MaterialsDepartment,UniversityofCaliforniaSantaBarbara,SantaBarbara,California,USA2:HongKongUniversityofScienceandTechnology,ClearWaterBay,Kowloon,HongKong3:HarvardUniversity,Cambridge,Massachusetts,USA

*Correspondingauthor:[email protected]—We report growth and room temperature continuous wave operation of InAs quantum-dotmicrodisk lasers grownonnominal (001) silicon substrates. Theactive structure containing five layersofInAs/GaAs quantum dots was grown by MBE on a GaAs-on-v-grooved-Si (GoVS) template produced byMOCVD.Microdisk laserswith4µmdiametersshowedcontinuouswave lasingatroomtemperaturewiththresholdsontheorderofhundredsofmicrowatts.AstatisticalcomparisonwithidenticallasersonnativeGaAssubstratesshowsthataveragethresholdvaluesforthetwocasesarewithin40%ofeachotherdespitefourordersofmagnitudedifferenceindislocationdensity.

Keywords—quantumdots,microdisklasers,siliconphotonics,heteroepitaxy,III-Vonsilicon

On-chiplightsourcesonsiliconarenecessarytomeettechno-economicrequirementsoflowcost,high device/bandwidth density, and low power consumption for high volume applications such asdata communication [1]. III-V integration on silicon by epitaxial growth is the de facto lowest costsolution compared to other methods such as flip chip bonding, die/wafer bonding, or externalcoupling[1,2].TherehasbeensignificantresearchlatelyonIII-Vquantumdotlasersepitaxiallygrownonsilicon,whichcanbeefficientlightemittersevengivenahighdislocationdensity[2,3].Tomeettheother requirementsof lowpowerconsumptionandhigh-densitydevices,quantumdotenabledmicro/nanolasersareattractiveduetotheirrobustnessagainstsurfacerecombinationcurrentsthatdominate at small device sizes, as well asmuch-reduced transparency/threshold current densitiesover quantum wells [2]. Here we report the room temperature continuous wave operation ofopticallypumpedmicrodisklaserswithverycompactsizeandlowthresholdsdirectlygrownon(001)siliconforlowcostmanufacturing.

A GaAs buffer was first grown on v-groove patterned (001) silicon by an Aixtron AIX-200/4MOCVD. The silicon substrate used was a nominal (001) wafer compatible with standard CMOSprocessing. A highly ordered, regular array of planar GaAs nanowires were first formed, andsubsequentlycoalescedtoformastandardplanarfilmwithadislocationandstackingfaultdensityof108 cm-2[3]. The remaining structure, comprising of a 1um GaAs buffer, a 600-nm Al0.7Ga0.3Assacrificial layer, and a 500-nm disk region, was grown in a Gen II MBE system. The active regionconsistedoffivestacksofInAsquantumdotlayers(2.75MLsdepositedat0.11ML/s,VIIIratioof35)embeddedin8nmIn0.15Ga0.85Asquantumwells,whichwereseparatedby37.5nmGaAsbarriersandenclosedbyouter50nmthickAl0.4Ga0.6Asbarriers(seeFig1).MBEgrowthtemperatureswere505°Cfor the active region and 600 °C for GaAs/AlGaAs as detected by a pyrometer. The same activestructurewasalsogrownonaGaAssubstrateforcomparison.

Microdisk laserswith4µmdiameterswerefabricatedbydry-etchingpillarsontheas-grownepiand selectively etching the sacrificial Al0.7Ga0.3As layer (see Fig 2). The fabricated devices werecharacterized in a surface-normal pump/collectionmicro-photoluminescence (μPL) systemat roomtemperature.Fig.3ashowsa representativesetofspectrameasured froma4-µmdiametermicro-diskonsiliconwithprogressivelyhigherpumppowerfroma532nmCWdiodelaser.Adistinctlasingpeak appears at 1308 nm and increases sharply in intensity, signifying the transition fromspontaneousemissiontolasing.Fig.3d&epresentthehistogramsofthelasingwavelengthforeachmeasuredmicro-diskontheGoVStemplateandGaAssubstrate,respectively.Thethresholdforthemicro-disklasersontheGoVStemplaterangesfrom130μWto410μW,withanaveragevalueof250μW, approximately 1.4 timesof the average value for lasers on theGaAs substrate (180μW). Theaveragethresholdofmicro-diskonGoVScorrespondsto50μWperQDlayer,comparabletothebest-reportedvaluesforInAsQDmicro-disklaserswiththesamecavitysizeonGaAsintheliterature.

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1. Zhou,Z.,Ying,B.,Michel,J.,On-chiplightsourcesforsiliconphotonics.Light:Science&Applications,4,(2015).

2. Liu,A.Y.,Srinivasan,S.,Norman,J.,Gossard,A.C.,Bowers,J.E.,Quantumdotlasersforsiliconphotonics.PhotonicsResearch3.5,B1-B9(2015).

3. Wan,Y.,Li,Q.,Geng,Y.,Shi,B.,Lau,K.M.InAs/GaAsquantumdotsonGaAs-on-V-grooved-Sisubstratewithhighopticalqualityinthe1.3μmband.Appl.Phys.Lett107,081106(2015).

Figure1.a,Schematicoftheas-grownstructureofmicro-disklasers.b-d,Cross-sectionalTEMimagesofthequantumdots(b),V-groovedstructure(c),andentireepistack(d).

Figure2.a,70°tiltedviewofthedisk.b,azoom-inviewofa90°tiltedSEMimageofafabricatedmicrodisk,revealingsmoothsidewall.c,top-downviewofthedisk,showingcircularity.

Figure 3 a, RT PL spectra of a microdisk on silicon taken at increasing pump powers. b, c,Integrated photoluminescence intensity (b) and linewidth (c) of the dominant mode as afunctionofpumppowerforthedevicein(a). d,e,HistogramsofthelasingwavelengthforallmeasureddevicesonSilicon(d)andGaAs(e),respectively.Theaveragelasingthresholdofthedevices within each histogram bar is denoted by the number displayed on top of it. Thenormalizedphotoluminescencespectraoftheun-processedsamplearesuperimposedinblue.