Effect of Surface Density and Mean Size of Quantum Dot on Properties of GaInAsP/InP QDL System

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1 IOSR Joural o Alied Physics (IOSR-JAP) e-issn: Volume 8, Issue 6 Ver. I (Nov. - Dec. 216), PP Eect o Surace Desity ad Mea Size o Quatum Dot o Proerties o GaIAsP/IP L System Ra'ed M. Hassa ad Eyma Th. Shirsha Deartmet o Physics, College o Educatio or Pure Scieces, Uiversity o Basrah. Basrah, IRAQ Abstract: I is work, we studied e eects o surace desity o quatum dots ad e mea size o quatum dots (s) o dyamics o quatum dot laser (L). Here, detailed eoretical study o e arameters eect o some roerties o GaIAs/IP L system at 1.55 μm waveleg. It icludes e ollowig variables: e reshold curret desity, coied level occuacy, iteral loss coeiciet, otical coiemet layer. I additio, it is diagosed eir role to determiig e amout o e maximum temerature o laser. By studyig a dieret cotrol rages o surace desity ad e mea size o s at idetiied otimum values or em. That gives better stability o e system's work ear e room temerature comared to exerimetal results. Keywords - Quatum dot lasers, Mea size o quatum dots, Surace desity o s, GaIAsP/IP laser. I. Itroductio The Quatum Dot Laser (L) has distictive characteristics i comariso to oer semicoductor lasers. The most imortat eatures ey have low reshold curret, weak deedece o temerature ad arrow sectrum [1]. The heterostructure semicoductor lasers was studied i comariso wi L, so it was iected carriers i wettig layers i e Otical Coiemet Layer (OCL), which is o bo sides (-), created a aroximate balace i e s system at room temerature. The occuacy o e uer levels o ga is a itegral art o OCL accomaied by a clear cesus i bo tyes o carriers i e OCL. These emselves carriers lead to e recombiatio radiatio curret, which deeds o e temerature, while it did ot cotribute to e lasig [2,3]. This mechaism based o temerature is also reset i e oer semicoductor lasers, but its lays a key role i quatum dot laser [4]. There is a sigiicat dro i e reshold curret desity o e double-heterostructure laser due to e resece o wide eergy ga i claddig layers. Limit e eectiveess o e carriers i e active regio ad e coeiciet o higher reractive eective area comared wi wettig layers. It s bee waveguide ad coies e light emitted i e active regio. The desity deiitio o laser actio ower begis is reshold curret desity ( ), so decrease do icreases i e otical outut ower at a certai iectio curret desity [2]. The most imortat actors which are take ito cosideratio durig e laser work are e iteral otical losses at have egative role o e laser outut. The otical losses i e laser outut is desired, while e iteral otical losses are oe o e uwated losses at occur i e laser cavity [5]. The iteral losses o system L associated to e carrier occuatio level i, as well as liked carrier itesity i e OCL. As a result o is associatio, which cotrolled by e reshold coditios, e desity o ree carriers are icreases wi e icreased e temerature sesitivity. The icrease i e amout o surace desity reduces iteral losses as a result o reducig e desity o carriers i e OCL. Which act to determie e amout o iteral losses at deed o e cross-sectio o iluetial o ese carriers [3,6]. By adotig a eoretical model o L [5], we will study e eect o cotrol arameters (surace desity o ad mea size o s) o each o: e carrier desity i e otical coiemet layer (OCL), e coied level occuacy i, e itesity o e reshold curret ad e amout o iteral loss coeiciet. So we ca deie oeratio eiciecy o e system wii e limited rage o e work temerature o e L tool. II. Theoretical Model The eoretical model based o e rate equatios ad it is simliied wii e steady-state. Fig (1)a shows e schematic structure o L system ad determie e shae o e otical coiemet layer ad quatum dots i e system. Fig. (1) b shows e eergy bad diagram o. DOI: 1.979/ Page

2 Eect o Surace Desity ad Mea Size o Quatum Dot o Proerties o GaIAsP/IP Laser Fig (1): (a) Schematic structure ad (b) eergy bad diagram o a [7]. Several mechaisms ca cotribute to e iteral loss o e laser such as e ree-carrier absortio i e OCL, scatterig at rough suraces ad imerectios i e waveguide [6]. All ese mechaisms ca be coveietly groued ito two categories, oe deedet o e carrier desity i e OCL ad e oer is ideedet. The which are associated wi e recombiatio i s,, ad i OCL, OCL, resectively, [7] ca be writte as: OCL is writte as [8]: Where ebrρ OCL ρ, OCL...(1) ρ...(2) are e ree-electro / hole desities i e OCL at e lasig reshold resectively, b is e OCL ickess, R is e radiative costat or e OCL material ad e is e electroic charge. ca be writte as [7]: ens...(3), where are e coied- carrier (electro or hole) level occuacies i s at e lasig reshold, Ns is e surace desity o s ad τ is e sotaeous radiative recombiatio time i s. The temerature-deedece o e ree-carrier desities ( ρ, ) acts as e maor source o such deedece o or which e carrier distributio below, ad at e lasig reshold is described by e equilibrium statistics (relatively high T) [6, 8, 9].,, N,,, 1, E ex[ T ρ, are deed exoetially o T [1] as;...(4), ]...(5) N, is e eective desity state i OCL, which ca be writte as [9]: DOI: 1.979/ Page

3 Eect o Surace Desity ad Mea Size o Quatum Dot o Proerties o GaIAsP/IP Laser 3 2 m, T, 2...(6) 2 2 N m, is e electro / hole eective masses i e eergy uit ad is ormalized Plack costat. The equality o e gai (g max ) to e loss (lasig reshold coditio) ca be writte as [3]: g max it...(7), L 1 r where β is e cavity losses ( l ) [5], r is e mirror acet relectivity ad L is e cavity leg. is e iteral losses coeiciet at ca be writte as e sum o two comoets which are e overall it iteral loss coeiciets, e irst is costat ( ) ad e oer icreasig wi e OCL electro desity [8, 11]: it,...(8) where σ is eective cross sectio or e iteral absortio loss rocesses. The exressio o saturatio gai coditio, g max, i OCL is [1], ca be writte as: g max 4 s 2 1 Ns...(9) a 1 where is e -size distributio uctio ( ) or e Gaussia distributio [7], is ormalized 2 Plack costat, is e otical coiemet actor i e layer, λ is e waveleg ad (a) is mea size o s. is homogeous lie broadig where [12]; q E q E...(1) is e root mea square (RMS) o relative -size luctuatios, eergy levels i a mea-sized ad q, E, l a ), which is aroximately costat to all modes. E, are e electro/hole quatized q, are e electro / hole quatized eergy levels where ( Oe ca write e coied-electro/hole level occuacies as [9];, 1,, 2, 1, 1, 2 g max 2 g max (11) From e temerature ideedet reshold coditio, e electro desity deedet iteral loss makes coules to,, as [9]: (12) 2 g max III. Results Ad Discussio There are may structure ad cotrol arameters lays iluetial roles i determiig e characteristics o e quatum dot laser by cotrollig e cocetratio o semicoductor materials or mauacturig temerature. Oe ca determie e cocetratio o e surace desity (Ns) ad e size o e quatum dots at will relect o several roerties i L system. We do carryig eoretical simulatig o e eoretical exressios usig Maematic system at alied to GaIAs/IP heterostructure lasig ear 1.55 DOI: 1.979/ Page

4 Eect o Surace Desity ad Mea Size o Quatum Dot o Proerties o GaIAsP/IP Laser m. We ll examie some actors i determiig e roerties o is laser, which deedig o e arameters listed i e Res [2,3]. Fig. (2)a show e carrier occuatio level i at icreases wi icreasig temerature. The eect o icreasig Ns is eective i reducig e amout o e carrier occuatio level i as a couterroductive relatioshi (see Fig. (2)b). At e same time, it does icrease T max o L system. I Fig. (2)a ere are two curve groes: wi e eect o iteral otical losses by absortio σ ad wiout it σ. Fig. 2. (a) Carrier occuatio level i,, vs. temerature, T, or dieret values o surace desity o s; Ns ( 1 1 cm -2 ) = 4, 5, 6, 7 ad 8. The curves are wi e eect o iteral otical losses by absortio ad e lies are wiout e eect o ese losses. (b)carrier occuatio level i,, vs. dieret values o surace desity o s, Ns, The arameters used or GaIAsP/IP L are [3]: L= mm, r=.32,λ= 1.55 µm, a = 15 Ao, E = 6. mev, ρ =.5, = 3. cm-1ad = cm 2, Γ =.6. The case is dieret whe icreasig e mea size o s. Thereore, we ote rough Fig. (3), e icrease o e arameter (a) will icrease e amout o e carrier occuatio level i, while is icrease reduces e amout o T max. So e mea size o s values must be selected close to 15 A so at e system works close to room temerature. DOI: 1.979/ Page

5 Eect o Surace Desity ad Mea Size o Quatum Dot o Proerties o GaIAsP/IP Laser Fig. 3.(a) Carrier occuatio level i, (A o ) = 13, 14, 15, 16 ad 17. (b) Carrier occuatio level i, o s, a (A o )., vs. temerature, T, or dieret values o mea size o s, a, vs. dieret values o mea size It ca be oticed via Fig. 4(a), e icrease o Ns arameter icreases e temerature T max, i.e., at has a ositive role o T max. While e eect o (a) arameter is show i e Fig. 4(b), at imact be egative as it icreases leads to a decrease o T max. Fig. 4. (a) Maximum temerature, T max, vs. surace desity o s; Ns. (b) Maximum temerature, T max, vs. mea size o s, a. DOI: 1.979/ Page

6 Eect o Surace Desity ad Mea Size o Quatum Dot o Proerties o GaIAsP/IP Laser O e ree-carrier desity i e OCL wi deedet o temerature, e imacts o e two arameters are maor source or e adotio o o T. So it is resosible or e carrier s distributio i e laser reshold. Oe ca observe rough e igure, e icrease i Ns will reduce i bo cases: whe ere are iteral laser losses deedet absortio or absece o ese losses art as it is i Fig. 5(b). Fig. 5. (a) Free-carrier desity i e OCL, s; Ns ( 1 1 cm -2 ) = 4, 5, 6, 7 ad 8. (b)free-carrier desity i e OCL,, vs. temerature, T, or dieret values o surace desity o, vs. Surace desity o s; Ns. The eect o e icrease o mea size o s leads to icrease wi decrease i T max, where it is show at it is workig o icreases o whe wi / wiout o iteral absortio losses o laser system as show i Fig. 6. DOI: 1.979/ Page

7 Eect o Surace Desity ad Mea Size o Quatum Dot o Proerties o GaIAsP/IP Laser Fig. 6.(a) Free-carrier desity i e OCL,, vs. temerature, T, or dieret values o mea size o s, a (A o ) = 13, 14, 15, 16 ad 17.(b) Free-carrier desity i e OCL,, vs. dieret values o mea size o s, a (A o ). The results shows e iluece o e cotrol o e s surace desity o e iteral loss i L system, which coect carrier occuatio level i, as well as wi ree-carrier desity i e OCL. As a result o is associatio, is is deedig o e reshold coditios wi e icreased o sesitivity to temerature ad e carrier s desity icreases. I Fig. (7)a, e results show a icrease i temerature will icrease e iteral losses almost liearly due to icreased ree-carrier desity i e OCL. Whe a crosssectio o e eective losses o iteral absortio has much iluetial σ, so would egatively aect e workig o e laser system. Whe σ, ca see a iteral losses stable is act i e certai value. The result shows at e icrease o Ns i e same temerature reduces iteral losses, where e eect o Ns egative o e iteral losses o L system (see Fig. (7)b). It also icreases is arameter to icrease T max as show i Fig. (7)a. The relatio betwee OCL ree-electro desity ad temerature is give where as exected e ormer icreases wi a icreasig o surace desity o s as e straight solid lie idicates. Fially, ere are sesitive relatio betwee e lowest excitatio eergy to e surace desity o s or a variatio o e costat loss coeiciet, mea size o s ad e mea size o s. DOI: 1.979/ Page

8 Eect o Surace Desity ad Mea Size o Quatum Dot o Proerties o GaIAsP/IP Laser Fig. 7. (a) Iteral losses o L, it, vs. temerature, T, or dieret values o surace desity o s; Ns ( 1 1 cm -2 ) = 4, 5, 6, 7 ad 8. (b)iteral losses o L, it, vs. Surace desity o s; Ns. The oosite case whe icreasig mea size o s leads to high amout o iteral losses i a costat temerature, ad e icrease o is arameter decrease e value o T max as show i e ig. (8). DOI: 1.979/ Page

9 Eect o Surace Desity ad Mea Size o Quatum Dot o Proerties o GaIAsP/IP Laser Fig. 8. (a) Iteral losses o L, it, vs. temerature, T, or dieret values o RMS o relative -size luctuatios; a (A o ) = 13, 14, 15, 16 ad 17.(b) losses o L,, vs. mea size o s, a. To cotrol e Ns values havig ositive role i e amout o, is role is achieved i bo o its arts i,e., ad OCL, as show i Fig. (9). The eect o icreasig e Ns work to reduce bo ad OCL ad icrease e amout o T max. it Fig. 9. (a) Threshold curret ad its comoets & OCL vs. temerature, T, or dieret values o surace desity o s; Ns ( 1 1 cm -2 ) = 4, 5, 6, 7 ad 8. Iset rereset carves its o curret ad its comoets & OCL vs. Surace desity o s, Ns. (b)threshold DOI: 1.979/ Page

10 Eect o Surace Desity ad Mea Size o Quatum Dot o Proerties o GaIAsP/IP Laser As show by Fig. (1), e eect o icreasig mea size o s work to icrease e amout o e reshold curret comoets, & OCL ad it decrease T max at e same time. Fig. 1. (a) Threshold curret ad its comoets & OCL DOI: 1.979/ Page vs. temerature, T, or dieret values o RMS o relative -size luctuatios; a (A o ) = 13, 14, 15, 16 ad 17. Iset rereset carves its Threshold curret ad its comoets & OCL vs. mea size o s, a. (b) This would be e case i e overall iectio wet ito s, ad e recombiatio curret i s would be temerature-ideedet. I actual Ls, e carriers are irst iected rom e claddig layers ito e otical coiemet layer OCL (which icludes e wettig layer), e catured ito e s. The resece o carriers i e OCL results i e recombiatio erei. Hece e recombiatio rocesses bo i s ad i e OCL cotrol ad its T-deedece. IV. Coclusio Based o e results o e simulatio o e eoretical model itroduced earlier, it is oticed at icreasig o surace desity o s o GalAsP/IP laser system, which has istrumetal eect i reducig e carrier occuatio level i wi a icrease i e amout o maximum temerature (T max ). It also wills reduces ree-carrier desity i e OCL ad reduce e amout o iteral losses. So it would be useul to icrease e surace desity o s wii e limits to kees e stability o e system. At e arameters values o e laser uder study, e otimum amout o surace desity o s is u to Ns (t) cm -2 to esure stable oeratig oit at a room temerature. While e eect o mea size o s, it would be cotrary to e studied L characteristics. It shows rough e results at a icrease o is arameter will icrease ad reduce T max,, itad. So, most maitai e relative -size o small values have ositive

11 Eect o Surace Desity ad Mea Size o Quatum Dot o Proerties o GaIAsP/IP Laser imact. Note at e otimum value o is arameter (o e L tye uder study) has limits o a ot 15 A to achieve better eiciecy. Reereces [1] Y. Arakawa ad H. Sakaki, Multidimesioal Quatum Well Laser ad Temerature Deedece o its Threshold Curret, Al.Phys.Lett. 4(11), 1982, [2] R. M. Hassa, C. A. Emshary ad S. I. Easa, Quatum Dot Laser: Tur-o Dyamics ad e Oeratio Characteristics, LAP LAMBERT Academic Publishig, 216. [3] G. M. Ali, Characteristic Temerature ad Lowest Excitatio Eergy o Semicoductor laser", MSc. esis, basrah uiversity, 215. [4] G. P. Agrawal ad N. K. Dutta, Log-Waveleg Semicoductor Lasers, 1st ed., Comuter Seiece ad Egieerig Series,VNR, Comay,New York, [5] Yuchag.Wu Theory o Modulatio Resose o Semicoductor Quatum Dot Lasers, PhD. esis, Virgiia Polytechic Istitute ad State Uiversity, USA, 213. [6] N. G. Basov, O. N. Krokhi, ad Yu. M. Poov, Productio o Negative-Temerature States i P-N uctios o Degeerate Semicoductors,SovPhys JETP. 13,1961, [7] L. V. Asrya ad R. A. Suris, Ihomogeeous Lie Broadeig ad e Threshold Curret desity o a Semicoductor Quatum Dot Laser, Semicod Sci. Techol. 11(4), 1996, [8] R. M. Hassa, C. A. Emshary ad H. A. Sulta, Eect o Quatum Dots Desity ad Temerature o Quatum Dot Laser Characteristics, Joural o Thi-Qar Sciece. 4(4), 214, [9] Li Jiag Theoretical Study o Perormace Characteristics o Semicoductor Quatum Dot Lasers, PhD. esis, Virgiia Polytechic Istitute ad State Uiversity, USA, 28. [1] L. V. Asrya ad S. Luryi, Eect o Iteral Otical Loss o Threshold Characteristics o Semicoductor Lasers Wi a Quatum- Coied Active Regio, IEEE J. Selec. To. Qum. Electro. 4(7), 24, [11] Y. Wu, R. A. Suris, ad L. V. Asrya, Eect o Iteral Otical Loss o e Modulatio Badwid o a Quatum Dot Laser, Al. Phys. Lett.. 1, 212, [12] L. V. Asrya, M. Grudma, N. N. Ledetsov, O. Stier, R. A. Suris, ad D. Bimberg, Eect o Excited-State Trasitios o e Threshold Characteristics o a Quatum Dot Laser, IEEE J. Qum.. Electro. 37(3), 21, DOI: 1.979/ Page

Carriers in a semiconductor diffuse in a carrier gradient by random thermal motion and scattering from the lattice and impurities.

Carriers in a semiconductor diffuse in a carrier gradient by random thermal motion and scattering from the lattice and impurities. Diffusio of Carriers Wheever there is a cocetratio gradiet of mobile articles, they will diffuse from the regios of high cocetratio to the regios of low cocetratio, due to the radom motio. The diffusio