Luận án Về hệ exciton và bonson giả một chiều

Chuong3. - QuanghQcphi tuyencuaQWW bandankichthichcao cacphituyenquanghQctrongchAtbandanduqcqUailsatkhibandanbi kich thichcaomanguyen hanthuanglabOimQtruanglaserm~. TuythuQcvao tUngv~tli~u,cuangdQmachumlasergayraphituyenquanghQcc6th~vao kholmgtit102denIOnban106Wfcm2.Dumnhfi'ngdi~uki~nnay,cacc~pdi~nfir - 16tr6ngduqcsinhranhi~utrongchAtbandan.cac hi~ulIngnhi~uh~tdotuang lac cuachUngtai chuanh6acAlltrucvilngnanglu<JIlgvadandensl;Tph1;1thuQc cuacacdaplIngquanghQcvaom~tdQcach~ttaiduqcsinhratrongchAtrAnbOi tfUanganhsang. Ph6quanghQcphituyendaduqcnghienCUllm~ metrongcach~bandan kh6ivaQW [30,40,41,98].Gfindaynhi~unghienCUllv~ph6hApth1;1(PLE)va phatquang(PL) trongcach~daylu<JIlgtirbandanclingdaduqcthl;Tchi~n.Cac congtrlnhthl;Tcnghi~m[2,14,16,35,50,65,90,91]lienhanhtrencach~giamQt chi~uchothAydmg,bellc~ vi~~cachi~ulIngexcitonictangdangk~sovmh~ bandankh6ivaQWnhumongdqi,ngumtadaphathi~nduqcmQts6d~ctrung qUailtrQngcuaph6quanghQcbandanmQtchi~u6nhi~tdQthAp,d6Ia:a)giatri nanglu<JIlgdinhexcitonictrongph6PL hallnhukhongdichtheom~tdQ[2,35]; b) 6 vilngm~tdQkhacaotrenm~tdQMott dinhexcitonicvanconrAtr6 ch-ung to tai h<Jpexcitonicchiemuu thesovmtaih<Jpvilng- vilng,trainguqcvmcac qUailsattrongbandanQW vakh6i6 m~tdQtuangduang[2];c) mQtky di ml;Tc Fermi(FES) m~ duqcqUailsatthAytrencaph6PLE IanPL. N61amchocuang dQph6quanghQcratsitcvaph1;1thuQcm~ vaonhi~tdQ[14,16,50,65,57,90]. TronghallbetcacBnhloanly thuyetv~ph6quanghQcexcitonchocacday lu<JIlgtirngumtasird¥ngmo hlnh chi baogommQtvilngcon thApnhAt[24,67,85]. 32 MQts6tacgiacotinhdenhi~uUngnhi~uwng connhungl~ib6quahi~uUng chfulcuapfflsma[11,35].Vi~cb6quamQtronghaihi~uUngnaylammohinh cuahQkhongduQ'cth1!cteHUnd~coth~sovmth1!cnghi~m. TrongchuangnaychungtasenghienCUllph6quanghQccuaQWW bang cachgiaiphuangtrinhBethe-SalpeterchodQcarnquangtrongkhuonkh6gfu1 dUngchfulfinhcotinhdendonggopcuanhi~uwng con.cacketquatinhtoan s6seduQ'csosanhvmcacketquatronggfu1dungkhongchfulHartree-Fockva vmcacketquath1!Cnghi~m. 3.1. PhbQuanghQcexciton:hapth1;lvaphanx~anhsang cac tinhchatquanghQccuabandfuIlienquanch~tchevmcacchuy~nmuclien vtinggiuawng dfuIvawng hoatrioTronggimh~ chixetcacchuy~nmucthlmg, hamdi~nmoi ngang(quang)cuabandfuIduQ'Cvietnhusan: E-L(W) =1+4'7IX(w), (3.1) trongdo X(w)la dQcarnquangtoanphfu1 x(W) = Ld%hXk(W), k (3.2) vm dlchla yell t6 ma tr~ lUOngc1!clien wng va Xk(w) la hamcarnquangphl;1 thuQcvectorsong.Sirdl;1ngly thuyetdapUngtuyentinh,dQc~ quangtoanphfu1 lienh~vmhamGreenc~pbmh~thuc: X(W) rv - L d%hd%~Gq--to(k,k', w). k,k' (3.3) TitphuangtrinhchohamGreenc~p(2.34),ngumtarutraphuangtrinhBethe- Salpeterhi~udvngchohamcarnquang[40]: Xk(W)=x2(w) ( 1- d:h L Vgh(k- k')Xk'(W)) ,""""'... k k' (3.4) 33 trongdo . XO(w)=-d€hl - j€(eiJ - jh(e~k) k k W - e€ - eh +irSk -k Ia hamearnquangh~ttMtVdo. (3.5) Phuongtrinh(3.4)Ia mQtphuongtrinhtfchphfulFredhomlo~ihai.Nghi~mso cuano duqctlmnhusan:Phfultichtichphfultheovectorsongtrong(3.4)thanh t6ngn di~mrmr~c j +OO dk n !:lkiL -t - -t L -. k -00 27r i=l 27r D~co dQchinhxaccao,ngumtathuCmgsirdvngcAllphuongGaussd~tinhtich phful.Chungtachuy~ntichphfultheovectorsongtrongmi~n[-00,+00]v~tich phfultrongmi~n[-1, +1]nhamQtphepd6ibien: ax k -t - 2'I-x vOia lamQth~soduong.SandosirdvngcongthuccAllphuongGauss-Legendre d~u6'cluqngtichphfultrongmi~n[-1, +1] +1 n Ii dx~(x)~ ~WiF(Xi)' trongdoXi lacaedi~mkhongcuadathucLegendrePn(x)vaWilacaetn,mgso Gauss-Legendre[1].Bangeachnhuv~y,chungtadaduaphuongtrinhtfchphful (3.4)v~mQth~n caephuongtrinhtuyentinhchoXi' Giaih~caephuongtrinh naybangphuongphapmatr~ nghichdaoho~cLV [71]chungtasenh~nduqc nghi~msochohamearnquang. ChuylaV(k- k') comQtkydi t~ik =k'.D~khirkydinayngumtaduathem vaomQthamF(k - k') naodonhusan 00 00 !dk'V;h(k- k')Xk'(W)= !dk'V;h(k - k') [Xk'(W)- F(k - k')Xk(W)] -00 -00 ... + II dk'V,h(k- k'JF(k - k'J) X,(w). (3.6)~ 34 F(k - k')seduqcchqnsaochoF(O)=1vatichphfultrongdatingocflcdoncuaso h~gthuhaTvephai(3.6)coth~tinhduqcchinhxac. D~thuduqcph6quanghqcgiongnhutrongthlJcte,ngumtaphaitinhdenca h~so tatdancuadQdun quangh<;tttaitVdo.H~so tatdanduqctinhbCriphanao cuanangluqngriengdQnghqc [41,42].Thy nhien&daychungWi chi dongian thaytatdanvo clingnh6c5trong(3.5)btmgmQthtmgso tatdanhi~ntuqnglu~ , =canst.Khi tinhdenh~sotatdan,di~mchuy~ntier gifi'agiatrihapthvduong vahapthvam(gain)khongconKayrachinhxact<;tithehoakethqpJ1=J1e+ J1h. D~vandambaodi~uki~nt<;tiw = J1 h~sohapthvd6idatinguaitathuangsir d~ngbi~udi~nph6choXo[40]: x~(w)=d%hJ dw' 2, 1- fe(w'- e~k)- fh(e~k)27f(w'- e%- e~k)2+ ,2 W'- W- ic5 . (3.7) ITITh~thuclienh~gifi'ah~sohapthv,phanx<;tvmhamdi~nmoiquang: n(w)+i~a(w) =VEl.(W),2w (3.8) ngumtarutrah~sophanx<;t: n(w)= ~ [ReEl.(w)+(ReEl.(w)2+ IrnEl.(w)2)1/2]~ jReEl.(w) (3.9) vah~sohapthvquang: W 47fW ' a(w)=- ( ) IrnEl.(w)=- ( ) Irnx(w),nwc nwc (3.10) trongdocvawIav~ tocvanangluqngcuaanhsang. B6 quaslJ phVthuQck cuayelltomatr~ lu5'ngclJc (giasird%h= canst), chungWigiaisophuongtrinh(3.4)choQWWGaAsvmcacthongsoT =50K, W = 20Eo,, = 1Eova..uh~duqccacph6quanghqct<;ticacm~tdQEHPkhac nhaunhulIencachinlJ..!f.3.1vaH.3.2.d daytansogiamnhotduqclaygiatri 35 1.5 T =50 K W =20 Eo 1= 1 E0 ?< E 0.5 n = 0.5 a~1 0 -0.5 -15 -10 n = 0.25 a~1 -1 n =1.0 ao -5 ( 0) - E~ ) / EO 0 5 HiOO3.1:H~sohapthvty l~v& phanaodQellIIlquangchoQWW GaAst~iOOi~td9 50K v& cacm~tdQkhacOOau. 0.8 0.6 n =0.25 a~1 0.4 ?< Q) 0.2 a: 0 -0.2 -0.4 -0.6 -15 -10 -5 ( 0) -E~ ) / Eo T =50 K W =20E 0 1=1E 0 0 5 HiOO3.2:Phanth\!CdQCftmquangchoQWW GaAs t~iOOi~tdQ50 K v& cacm~tdQ khacOOau. ......... 36 khaIan(W =20Eo~ 92meV) d6philhqpvOimohinhmQtvilngcon.T~ m~tdQ bangkhon~,ph6h~pthl;1cho th~ymQtdinh cQnghuangexciton(tr~g thai n =1) t~inangluqng-5.7 Eok6 tUdayvilnglienWctuanglIngvOinangluqnglien ketexcitontrantrongQWW.cac tr~gthaiexcitoncaobanflamsatdayvilng lien tl;1ckhongqUIDsatdu<JCdo dQtatdanIan. Khi co m(ttEHP, cacb6 chinh nhieuh~tlamgiarncu<mgdQdaodQngti':r(oscilatorstrength).VOi slJ tangm~t dQplasmavilnglienWcd!chnhanhvemiennangluqngth~p,trongkhidodinh excitonth~pnh~td!chr~tit.NguyennhancuaslJd!chit ladocoslJbtitri.rgifi'a dQcokhevilngvadQgiarnnangluqnglienket.T~im~tdQcao,n = 1aol,the hoaxfunnh~psfiuvaovilnglientl;1c.Cachi~ulIngl~pd~yvilnggfiyraslJkhuech d~itru<mganhsang(opticalgain).Dieunayth6hi~n6h~soh~pthl;1bellduOithe hoanh~ giaIT!funmotaslJphatquangcarnlIngcuabandart. De th~yro hi~ulIngexcitonic6 cacm~tdQtrenm~tdQMottnM,chungta tinhh~sotangcu<mgexcitonic(excitonicenhancement)p,lad~iluqngdu<Jcd!nh nghianhusau: - Imx(w) p(w) = ImxO(w)' (3.11) trongdoX la dQcarnquangtow phan,XO= I:dehx~la dQcarnquangcuah~ttai k tV do. Chu y lacacdQcarnquangX vaXO khacnhau6 cho:X co tinhdentUang tachutCoulombgifi'acacdi~ntirva10trongtrongkhi XOtbikhong. Hinh3.3veph6p(w)vOicacthongsogiongnhuH.3.1vaH.3.2nhungt~icac m~tdQkhacnhauvaIanbanm~tdQMott(nM~ 0.53aol).cacketquatinhso cuachungWi choth~ymQth~so tangcu<mgp Ianbell trendayvilng(dayvilng du<JCchi rabdi cacmtli ten)vap co mQtdinh6 ganV!tri giftthehoaJ.1(thehoa du<Jchi rabdicacduCtrgv~chdQc).M(tcdtitrenm~tdQMotttr~gthailien ketexcitonkhongcoIlt6nt~inhungthehutCoulombvartlamtangkhanangtim... ~7 .. 3 T =50K W =20Eo y=1E0 2.5 2 a.. 1.5 -. -'-' t,l 0.5 -15 -12.5 -10 -7.5 -5 ( ffi - E~) / EO -2.5 0 HiOO3.3:DQtangcuangexcitonictronggandungchtmt~id.cm~tdQkhacOOautren m~tdQMott:n =0.6aol (duanglien);n =1.0aol (duangg~ch);n =1.5aol (duang g~chchfun).cacmfiitenchidayvUngt:iichufuth6avacacv~chdQcchitheh6afJ. 0 -10 -8 -6 ( ffi - E~) / Eo -4 -2 HiOO3.4: DQ tangcuangexcitonictronggandungchtmt~icac OOi~tdQkhacOOau: duanglienU'ngv6iT =JO K vaduangg~chU'ngv6iT =20K. cacmfiitenchiday vUngt:iichufuth6avacacv~chdQcchitheh6afJ. .......... 38 51- W =20 Eo n =0.5a 1 4 Y=1 Eo I 3 a.. 2 th~ydi~ntirva16trongt~clingmQtch6.Di~unaygayramQtS1;ftangcuang excitonic~rongph6quanghQcplasma.T~iV!trigfulgillthehoa7 cacdi~ntirva 16trongcoth~daodQngd~dangban(chuy~ndQngquId~ocuachungit b!h~ chebCringuy~nly Paulidococactr~gthaib!chiemvatrongnfungfulMall) vi thecuangdQdaodQngexcitonicl:Jdaym~ nh~t. S1;fph\!thuQcvaonhi~tdQcuah~sotangcuangexcitonicduqcphantichtr~n H.3.4.Do th!choth~ydinhph6tangsacnetbanl:Jnhi~tdQth~pban. Chinhs1;f biend6i saccuahamFermit~ithehoagayra s1;ftangm~nhcuap(J1).Khi nhi~t dQtang,c1;fcd~ cuap(w)giamdos1;fml:JrQngnhi~tcuahamFermi. S1;fki~ncomQtdinhtangcuangexcitonicb quanhV!tri thehoatrongph6quang hQct~ nhi~tdQth~pdfiduqcbietdentrongcach~khoi [42,51,98].Tuy nhi~n trongcach~th~pchi~u,hi~uUngnayd~cbi~tm~, dinhtangcuangexcitonic trbn~nr~tsacvangumtagQino laky d!t~im1;fcFermi(xem[48,52,78]). 3.2. Hi~ull'ngnhieuvungcon MQthi~uUngquantrQngcuacach~bandfulb!giamnhotluqngtir13.sv tach racuacacviingnangluqngcon(luqngtirhoadogiamnhot).TrongtfUanghqp giamnhotr~tm~, khoangcachgiuacacviingconlan,ngumtacoth~sirdvng mohInhgomcomQtviingdfulvamQtviinghoatr!tuangUngvmcacviingcon th~pnh~tcuadi~ntirva16trongnhub tr~n.d cacdi~uki~nnhucuangdQgiam nhotwa phaiho~cnhi~tdQcaoho~cm~tdQh~taiIan(kfchthichm~), cac h~taicoth~chiemch6v6isoluqngIantr~ncacviingconcaobanvacachi~u Ungnhi~uviingcontrbn~nquantrQng. Bennerva cQngS1;f[11,35]13.nhUngngumdatiti~ntinhloanph6h~pthvva PL choQWW vmmohinhnhi~uviingconmQtcachcoh~thong.Tuynhi~nhQ 7trongtwanghqpT =~J..heh6achinhIiinangIuqngFermi:f1==EF 39 chinghienCUlll:Jtrongkhuonkh6HFA, tucIab6quahi~uUngchancuatuanglac CoulomlJ<a.VOily thuyetnay,m~cdil diico gangd~lamphilhqpkefqualy thuyet vOikefquathlJcnghi~m[35](bangcachthayd6icahaithongsom~tdQvanhi~t dQ)hQvanphaithilanh~ comQtSlJdichdinhph6(tinhloan)kham~ theom~t dQ,trongkhi thlJcnghi~mchothaydinhnayhallnhudUngyen.MQtCallh6i d~t ra la li~ucophaislJ b6quahi~uUngchantrongtuangmcdii gayra slJdichdinh ph6trongkefqualy thuyethaykhong.Cactinhloancuachungtoi trongmvcnay chuadlJllgcahi~uUngchanIanhi~uUngdavilngconsetra1mCallh6i do. Trongtruanghqpconhieuvilngconngumtaphaitinhcacyelltomatr~n tuangmcCoulombtrangiftacach~taitrencacvilngconkhacMall: v;tsm(q)= 2:~ejf dyf dy'4>~(y)4>;(Y')4>s(y')4>m(y)Ko[qly- y'lJ, (3.12) trongdo,4>nlacachamrieng(1.4).Bi~uthucgiaitichchocacyelltomatr~ nay duqcchoboo[11,18]. T6ngquatbanphuongtrinh(3.4)chi chovilngconthapnhat,cacdQcam quanglienvilngcontuantheohfcacphuongtrinhtichphansan[7,35]: Xl(k,w)= x?(k,w)- x?(k,w)d:hLV~~'ll'(k- k')XI,(k',w),k',l' (3.13) trongdoi,i' Iacacchisovilngcon,dehlayelltomatr~ luangclJclienvilngvOi giasirkhongphVthuQcvaovectorsong,V~~'ll'(p)latuanglacCoulomblienvilng conchantInh,X?ladQcarnquangh~taitt;rdo: X?(k,w)= -deh1 - fe(ek,l)- fh(ei,l)w - ee - eh +. .k,l k,l '//Y (3.14) Trongbi~udi~nph6noduqcchoboo: XO(kw ) = dehrdW' 2, I-fe(w'-eil)-fh(eil)I , 2 ( ' e h "~ 7r W - ek,l- ek,I)2+ ,2 W'- W- i6 40 ... e + h ~ deh ek,1 ek,1 - W (W - ek,1- e~,I)2+,2(1- r(e%,I)- fh(e~,I)) + ideh , (w- ek,1- e~,1)2+,2 (1- r(w - e~,I)- fh(e~,I)), (3.15) trongdonangluqngh~tdantaichuanhoatrenm6ivimgconla: , . . fi2k2 Eo . e~,1=cfc,1+llf(k)=2m'+f +lWj +llf(k),J (3.16) b day lll(k) =Re~l(k,c{- jJ)+ib) (3.17) Ia dQtaichuanhoanangluqngh~tdandoEHP. V6i nangluqngrieng~l(k,z) tinhtronggfu dungchartb~cchinh: "j (k ) rv 1 '" ujj (k k' I)COj (k' I)UI ,Z - -- {3~ vS,ll'll' - ,z - Z 1'1' ,Zk',z',I' (3.18) dQtMchuanhoanangluqngh~tdanvtingcon l co th~vietnhusau: ll{(k) _~{HF(k)+~{corr(k), (3.19) trongdo ~{HF(k)=- L ~l~I,(k- k')fj(c{',I')' k',I' (3.20) Ia nangluqngriengHartree-Fockva~{corr(k)Ia nanglu<;mgriengtuangquail. - Trongkhuonkh6gfu dungcl.,Icplasmon,nangluqngriengtuongqUailduqc chobbi[88]: ~{corr(k) 2 - '" v.jj (k- k') Wpl,ll'lI'- ~ lI'lI' k',I' 2Wk-k',ll'll' f l +g(Wk-k'lI'll')- P (c{,I') g(Wk-k'll'll')+P (i!.k " I') ] X ' . ' , + j'j , (3.21) cfc1- cfc,I' - Wk-k'lI'll' ck I - ck'I' +Wk-k' ll'lI'"""' " , " , 41 vatuangtaeCoulomblienviingeh&ntlnhcod~g: .. TTeh ( )_V,eh ( ) (1 W;I,llllll(q) )vS,ll'll' q - ll'll' q - 2 'Wq,ll'll' (3.22) trongdo 2 ( ) - " ~~'IIII,(q)nl"q2wplll'll' q - ~ , , I" . ~I'lll(q) mj,J 2 2 ( q2 ) q4 Wq,ll'll'= Wpl,ll'll,(q)1+ ~ + 4~'/'i,ll'll' m l: ~~'IIII,(q)jj(cLII)(1- jj(c{llI)) 2 I",j,k ' , 2 /'i,ll'll'= 2(3 2 j Wpl,ll'll"l: ~IIIIIII'(q)nk I"/mj I",j , v6inlla m~tdQh~trenviingconl. 0 T=50K W=5E 0 -2 -4 0 W--- w -6 -8 -10 0 0.5 1 nao 1.5 2 HiOO3.5:BGRhaydqtaichuanhoavtingconth~pOO~tcuaQWWGaAstheom~tdq plasmatrongcaegill dungkhacOOau. Trang trUanghqp-boquahi~uUnggi~tlid, Wela bo quadonggopeuac{,1- E{,1' trong (3.21), nguC1i..taco th~viet bi~uthueeho dQtai ehuanhoa nang luqng h~t 42 .. (a) T =300K W=5E 0 y=1 E0 (b) T=50K W=5 E 0 y=1 E0 - ::J cu-- - ::J cu-- 4 c 0 :+::; a.I.- 0 C/) .0« c 0 ~ 0...I.- 0 C/) .0« 5 -10 -5 0 5 10 -10 -5 0 5 10 ( co- E~) / Eo ( co- E~) / Eo Hinh3.6:Phi)hllpthl;1cuaQWW-GaAst'.linhi~td<)300K (a)va50K (b)tronggan dungkh6ngchanHF (cacduangg'.lch)vagandungchantInh(eaeduangli6n)v& cae m~td<)plasmakhaenhau:1)n =0; 2) n ::: 2.1 X 105em-i; 3) n ::: 4.2 X 105em-i; 4) n::: 6.3X 105em-i; 5) n::: 8.3X 105em-i. dantronggandunggill tinhnhugall: !l{(k)=- L Vd,{l'll,(k- k')fj(c{',l')+~L (Vd,{lllll(k')- Vz{,1I,(k')).~~ ~~ (3.23) Neungumtasirdvngthetuangtackh6ngchanV thaychothetuangtacchan tlnhVstrong(3.23)va(3.13)ngumtanh~ l~du<Jch~ESEtrongHFA [35]. TranThoaivacQngslJ [88]dfitinhroansodQtaichufuhoanangluqngnhi~u... vlingcon(SBR)choQWWGaAs.DocoslJphfulbocach~tadlencacvlingcon'-.. 43 caoban,BGR (haydQtii chuAnhoavilngconthapnhat~Eg= L ~{=o(k=0)) j=e,h giarnsovOimohinhchi xetmQtvilngcona clingm~tdQplasma.Hinh 3.5bi~u di~nBGRnhumQthamcuam~tdQchoQWWGaAsvOiW =5Eo,T = 50K. (j day,BGR du<JctinhtrongbagandungkhacMall: gandungHartree-Fock,gan dungchangiaanhvagandungchandQng. Ph6hapthvty l~vOiphanaodQcarnquangtoanphandu<JchobCiih~thuc: a(w)rv Imx(w)=ImL:XI(k,w). l,k (3.24) GiMcacphuongtrinhtichphan(3.13)tinhden3vilngconthapnhat(sirdvng matr~ rv 600x 600trongCallphuongGausstrongkhonggiank vai I k I <kma:IJ chungtoinh~ du<Jcph6hapthvquangnhumQthamc~anangluqng.Hinh3.6 choph6hapthvcuaQWWGaAsa nhi~tdQphongT = 300K (a)vaa nhi~tdQ thapT =50K (b)tronggandungchan(cacduangli~n)vatrongHFA (cacduang g~ch)vOicacm~tdQkhacMall. cac thongsosirdvngtrongtfnhtoannayla: khonggianli~nvilngconW =5 Eo ~ 23meV; hangsoHltdanhi~ntuqnglu~ 'Y=1 Eo ~ 4.6meV. T~ m~tdQbangkhong,cahaigandungchoketquadong nhat.Dlnhthunhatcuaph6hapthvchiranangluqngli~nketexcitontrantr~g thaicobanla Eb=3.6Eo ~ 17meV. &.rchuy~ntiepgifi'acacvilngconco th~ qUailsatratro tr~nph6hapthvnhacacdinhcQnghuangexcitont~igandaycua m6ivilngcon.Khi m~tdQtang,hi~ull'ngchancuaplasmatran~nquailtn;mgdaTI dens1!khacbi~tgifi'ahill gandungchanvakhongchan.TrongtfUangh<Jpnhi~t dQcao(300K) s1!khacbi~tnaylakhanho.Ph6excitonicdichdokhi m~tdQdi~n tir- 16trongtangtrongcahaigandung.Trongtruangh<Jpnhi~tdQtuangdoi thap (50K) chUngtoi timthaymQts1!khacbi~tIan gifi'agandungchanvagandung khongchan.Trongkhi gandungkhongchandongianlamcuangdQph6tang m~ t~thehoadfu!dens1!dichdlnhph6,gandungchanchothaydinhexcitonic 44 -1 -10 -5 0 ( 0) - E~) / EO n=4.2104em-1 n=8.3104em-1 n=1.7105em-1 n =2.5105em-1 n=5.0105em-1 n =8.3 105em-1 n =1.3 106em-1 5 10 Hinh3.7:Ph6hapthl;lcuaQWWGaAst~inhi~tdQ50K tronggandungchtmfinhv6i caem~tdQplasmakhacMall. thunh[(thallnhukh6ngdichtrongmQtvi1ngIOncuam~tdQplasma(Hinh 3.7). T~inhUngm~tdQcaonhu8:3x 105va 1.3x 106em-I, thehoanambell tren vi trfnanglu<JI1gexcitonicthunh[(t.Hinh 3.7chUngtomQtco mQtexcitonicgain m~ trongvi1ngh[(pthvfunbellduoitheboa. 3.3. Ph.}PL: Sosanhly thuyetvOith1;lcnghi~m. Trongmvcnaychungt6i thlJchi~ncactfnhloans6choph6PL cuaQWW GaAs vasosanhcacketquathuduqcvOicacketquathlJcnghi~m. Ph6PL duqcxacdinhtitphanaocuadQcarnquangloanphanbbi c6ngthuc: Imx(w) dehR(w) I'V = 1m" X (k W)... e(3(w-/-L)- 1 e(3(w-/-L)- 1 ~ I , .l,k (3.25) Chungt6i tfnhR~~t~inhi~tdQplasmaT =50K vOicacm~tdQEHP khacnhau 45 3- I T =50 K W=5 E 0 21 y=1E.-. 0 ::J rn-- c:: 0 1 :;::; a....... 0 CJ) ..c« 0 (tir n ~ 8.3x 104em-I denn ~ 1x 106em-I) tronggill dungHartree-Fock h6ng chillivat;onggill dungchillitioo. HiOO3.8tuanglffigvOigill dungHartree-Fock.Tronggill dungnaydiOOPL ph\!thuQcm~ vaothehoaloanphill vaco cacgia tq ky di: khi m~tdQtang, diOOPL dichxanhtheothehoad6ngthainotangdQtngQtm6ikhi thehoagill vOi cactill s6 daodQngcQnghuOngexcitonic.Ky di naychlOOIa ky di mlJcFenni machungtadanoi dena tren.TuyOOientrongHFA, nobi daOOgiaquacao.VOi gill dungnay,d~lamphilhqpvOithlJcnghi~mBennervacQngslJ [35]daphai tlOOPLa nhi~tdQkhacao(khirFES bangslJmarQngOOi~tcuahamFenni)d6ng thaitangOOi~tdQkhi m~tdQtang.Tuynhienkhi madangdi~ucuaph6toraphil hqpthl dinhexcitonicl~idichdokhanhi~usovOithlJcnghi~m. T=50K E~=1.6eV W=23meV 'Y=4.6meV--- ::) >-+-' "00 c: Q)+-' c: --.J 0... n =2.5x105em-1 - n=1.0x106em-1cd-- n =8.3x105em-1 4 -1 I - n=8.3x10 em --: n =5.0x105cm-1 1.54 1.56 1.58 1.6 Cl)(eV) 1.62 1.64 HiOO3.8:Ph6PL cuaQWWGaAst~iOOi~tde?T =50K v6icaem~tde?khacOOau trongHFA. .... """"'" 46 .- :::::I rn-- >...... "00 c: a.>..... c: J 0... .- :::::I rn-- >...... CJ) c: a.>..... c: J 0... a) T =50 K E~= 1.6 eV W =23 meV 'Y=4.6 meV - n=1.0x106cm-1 - - n =8.3x105cm-1 .-. n=5.0x105cm-1 n=2.5x105cm-1 - n =8.3x104cm-1 1.54 '1.62 1.641,56 1.58 1.6 0) (eV) b) T =50 K E~=1.6eV W =23 meV 'Y=4.6meV - n = 1.0x106 cm-1 - - n=8.3x105cm-1 .-. n=5.0x105cm-1 .", n=2,5x105cm-1 - n =8.3x104cm-1 1.54 1.56 1.641.58 1.6 0) (eV) 1,62 Hinh3.9:Ph6PL cuaQWW GaAst<:linhi~tdQT =50K v6icaem~tdQkhacnhau tronggandungchtmaciIv6inangluqngriengtinhtronggandungchtmdQng(a)vav6i nangluqngriengtiRll.,!I°ngandunggiiianh(b). 47 ... - 625W/cm2 - - 260W/cm2 .-. 175W/cm2 .... 45W/cm2 " "',:J / \ I I I I /', I ' I ; \ I I \ I ' I " I I / I / / /,. / / / -'7.~.~~-:.-J' -- ~ >....... CJ) c <J.) ...... C "' \ , \ \ \ , \ ,, \ \ \ \ 1.43 1.44 1.45 1.46 1.47 Energy (eV) moo 3,10:Ph6PL thl!cnghi~mchodayluqngtirdi6ubienInGaAsfGaAs6 OOi~td<') thapthl!chi~nbmGreusvac<')ngSl![35].Dayluqngtirduqckfchthfchbangxunglaser v6icaccongsuatkhacOOaud~t~oracacm~td<')e-hkhacOOau, - Ops - - 200 ps .-. 400ps .. .. 800ps - 1.4ns - - 2,0ns \ -- :J ro-- >....... 'en c <J.) ...... c \ \ ". ," ,'" \ \ \ / / \{-- ./~ \. \ , '. '. - . 1.54 1.56 1.58 1.6 1.62 1.64 Enerqy (eV) moo 3.11:Ph6PL thl!cnghi~mchodayluqngtirGaAsd~g-Vt~iOOi~td<')plasmarv 50-60K thl!chi~nbmAmbigapathyvac<')ngsl![2].DayluqngtirduqckfchthfchleD tr~gthaim~td<')e-hca£?bmcacxunglasercongsuatrv 500Wfcm2,NguOitadoPL t~icacthOidi~mkhacOOausaukhinglrngbarn. """'", 48 '--" "-- _.-..- , . . . . 1.48 1.49 1.5 Ph6PL tronggfudungchtmduqcchotrenHinh3.9.Trongdo,H'mh3.9(a) tuangUntvm nangluqngriengtinhtronggfu dungchtmdQngchothaydinh excitont~i1.585eV.Hinh3.9(b)tUangUngvmnangluqngriengtinhtronggfu dunggiaanhchothaydinhexcitont~i1.582eV. Sl!khacbi~tv~V!tri cuadinh excitontronghaigfudungnayladoslJdanhgiacaonangluqngriengtronggfu dunggiaanhsovmgfu dungdQng(Hinh3.5).Chungtanh~ thayhi~uUng dangchuytrenH'mh3.9la: dinhexcitonicd!chratit vmslJ tangm~tdQ(dQ d!chclJcd~ila 1.1meV).cack€t quatinhloanly thuy€tnaycuachungtoiphil hqpkhatotvmcacdod?cgfu daythlJchi~nlIencacmalldayluqngri':rGaAs hinhchfi'V t~nhi~tdQplasmaU<1Cluqngrv 50-60K bbiAmbigapathyvacQngslJ [2],dingnhuphilhqpvmcacthlJcnghi~mtrencacdayluqngri':rdi~ubi€n kich thichInGaAs/GaAs0 nhi~tdQthapbbi nhomcuaForcheI[35](cack€t quathlJc nghi~mduqcminhhQatrenHinh 3.10va3.11). Tu phfuthufunhatcuaBSEchungtoitinhduqcm~tdQMottchoh~QWW vmcacthongsonhutrenIa:nMc:::0.5aolc:::4x 105em-I.Daylam~tdQmat~i donangluqngexcitonsatnh~pvaodayvlinglienll;1c.Caobanm~tdQMot!,tr~g thailienk€t excitonkhongcont6nt~.Tuy nhiennhuco th~thaylIen Hinh 3.9, dinhexcitonicvanti€p tl;1Cduytri vakhongd!cht~im~tdQlend€n 1x 106em-I Wcla tUangduangvm1012em-2trongbandanQW ho~c1018em-3trongbandan khoi. Chuy la nhfi'ngm~tdQnayIanbankhanhi~unhihlgm~tdQlamchodinh excitonictrongbandanQW vakhoi tri~tlieu.Nhuv~y,philhqpvm [2]chungta k€t lu~: trongbandanmQtchi~u,phatx~excitonicti€p ll;1chi€m uu th€ sovm phatx~vling- vling(h~ttMtVdo)0 nhfi'ngm~tdQ(tUangduang)caobansovm bandanQW vakhoi. Nguyennhancuahi~ntuqngnayla do slJ chtmy€u trong h~mQtchi~udand€n cacdi~nfirva16tronghapdannhaum?nhtrongvlinglien... ll;1c.Phaid€n m~t~~ratcaocuaEHPdinhtangcuangexcitonicmmb!Ianat. 49 .. -,- -,- 1515 1520 1525 Energy(meV) (a) n = 5.105 cm-1 :J ~-- ,.......:.. .: .:r:.. .... .. .... ..I : :. 1.7K : :~ ~ :,.. :\... ~ ..3 K : .:.! :\..., . ~K ~,,:. . '-, . ~" ". ;, 10K~ -- ',---- ./ '.. 20K /' '-...---. ~ 30 K ...,...",.-. ~ --...-- >.:~ en c <D+-' C ...J a.. HiOO 3.12:S1!phVthuQcOOi~tdQcilaph6PL trongdayluqngttrGaAs: (a)Ket quathvc nghi~mcilaCallejavacQngsv[14Jchoion-milledQWWv6im~tdQplasmauacluqng la5x 105em-I,kh6ng ianlienvimgcanxacdiOOtittanx~Ramanla5.2:!:0.5meV; (b)Ketqua19thuyetronggfuldungchaotioov6in =0.6aiJl ~ 5 x 105em-I va W =1.13Eo ~ 5.2meV. Ph6PL cilaQWW GaAschocacgiatq khacnhaucilanhi~tdQdu<Jctinhtrong Hinh3.12(b)sird\lngcacthongs6:m~tdQn =0,6aiJl ~ 5 x 105cm-I, khong gian lien vimgcon W =1.13Eo ~ 5.2meV. cacthongs6naydu<Jch9nphil h<JPvmcacdfi li~uthl.Jcnghi~mcilaCallejavacQngsl.J[14].D~sosanh,ph6PL quansattr~mgthl.JCnghi~m[14]du<Jcbi~udi~ntrongH.3.12(a).Hinh 3.12cho thayco svphilh<JPratt6tgiUaly thuyetva thl.Jcnghi~m:1)b nhi~tdQthapdinh PL tangratsact~iIanc~ giii thehoaJ.1(nhudad~c~pb tren,trongcach~thap """... 50 (b) n=5.105cm-1 W =5.2 maV y= 4.6 maV --. :J 5K >.+-' '00 I 7 Kc <D+-' C ...J I 10K a.. I 15K- 20K- 30 K I -8 -6 -4 -2 0 2 (0) - E ) / Eo chi~u,dinh nay du<Jcgqi la FES). Khi nhi~td<)tang,tan x~nhi~tquanhthe hoa tangHungifund<)doccuaph6dfuldenFES gifunva bien ffi~tt~inhi~td<)cao; 2) dinh PL cho th~yco ffi<)tslJ dich do khi tangnhi~td<).cac ket qua nay cling phil hqpv6i.cac ket qua thlJc nghi~ffigfinday b6i Rubio va c<)ngslJ [73]. Tren Hinh 3.13 chung toi ve ph6 PL trong HFA su dvng clingcacthongso nhuH.3.12(b)d~sosanhv6i.cacketquatronggfindungchill. Giongnhudffchi ra lIen H.3.8,cuangdQcuadinhph6co ffi<)tgia tri di thuang:no tangd<)tng<)t trongtwanghqpJ1liendengfinv6i.giatri t~nsodaod<)ngc<)nghuangexcitonic. n =5105 cm-1 W = 5.2 meV y= 4.6 meV -6 -4 -2 ( co- EO) I E 9 0 0 2 Hinh 3.13:Ph6PL tronggftndungkhongehanHartree-Foekt<,iicaenhi~td<)khaenhau v6'icaethongso giongH.3.12(b). Tit cacketquatrenH.3.12vaH.3.13chungtoiconh~ xetnhusau:Sov6i. cach~2Dva3D,FES,J6nhO'Iltrongh~ID ladohi~uU'ngchill trongh~nayyeu hO'Il,hi~uU'ngl~pd~,khong ianphatr6nenffi~, d~cbi~t6vilngnhi~td<)th~p. 51 .-. ::J cci-- >.- Ow c IQ.) 5K- c- I 7K---I a.. 10K 15K- 20K 30K'--- -8 M~cdli chinhhi~ulffigl~pdaykhonggianphadffgaylienPES vachiemUtithe nhunghi~ lffigchtmclingvanconr~tqUailtn;mg.Neub6quahom tom sv chtm cuaplasma,PES sebtdanhgiaquacao(nhutrongtruangh<JpHFA khongchtm trenH.3.13)dandencacketquatrainguQcvoi cacketquathvcnghi~m. ....--. ::;j 0.8 ro----- >- :t= 06 (f) . c: Q)+-' c: (f) 0.4 W LL 0.2 - Theory 0 V-groove . ion-milled 0 ~ 0 0 10 20 T (K) 30 40 HiOO3.14:CuangdC)c\Tcd~iph6pi OOumC)thamcuaOOi~tdC)trongtlOOto<ln1ythuyet (duangli6n)sosanhv& ketquath\TCnghi~mtrencaedfiyhiOOchitV [90](0)vatren caedfiyion-milled[16](.). Hinh 3.14bi~udiencuangdQcvcd~icuaph6PL theonhtetdQ.Ket quatinh ~ toanly thuyet(duangli~n)duQcsosanhvOicacdfi'li~uthvcnghi~m[90]tren cacdayion-milled(.) vatrencaedayhinhchfi'V (0).cac cuangdQph6dffduQc chufulhoat~inhi~tdQdoth~pnh~t(T rv 2 K). cacketqualythuyetcuachung toichoth~yPESph\!thuQcm~ vaonhi~tdQ:nosuygiamnhanhkhinhi~tdQ tangtic2 K den40K. SovOithvcnghi~m,sVgiamcuaFEStrongtinhtoanly thuyetyetihaIl.Di~unay coth~ladochungWidffkhongtinhdensVph\!thuQc --~ 52 nhi~tdQcuah~soHitdfu, (h~sotatdfudu<JcmongdqiIatangtheonhi~tdQ [42]bCriVIchuy~ndQngnhi~tgiatangcacquatrinhtanx~giUacach~taivalam giamthaigiansongcuatr~gthaiphfulqrclienvimg). T6ml~itrongchuongnaychungWidfftfnhph6hapthv,ph6PL cuaQWW kfchthfchquangbangcachgiaiBSEc6tfnhdenhi~uUngChIDcuaEHP.d vimg nhi~tdQkhathapchungtoi dfftimthaymQtkhacbi~tIansov& gfu dungbo quahi~uUngChIDHartree-Fock[10,35].Cacsosanhv& caccacketquadod~c [2,14,15,16,17,35,90]chothay:trongkhi HFA hoantoanthatb~ithig~n dungChIDcuachungWitorakhatottrongvi~cmotathvcnghi~m.Ly thuyet cuachungtoidffgiaithfchdu<Jcacd~ctrungcabantrongph6quanghQccua cacd~ybandankfchthfchcaod6la: 1)T~inhi~tdQrv50K, c6mQtsvbil tmIannhaugfunhuhoantoangiUaBGR vacacb6chfnhdinh(baog6mcahi~uUngChIDvalapd~ythonggianpha).Ket qualadinhexcitonh~unhuthongdichtrongmQtvilngm~tdQkharQng:tu0den bon 106em-1. 2)Trongcach~bandanmQtchieu,hi~uUngChIDtuongtaccuaEHP khayeti(so vaih~bandankhoivaQW). Nho d6,cacdi~ntirva16trongc6th~tuongtachut v& nhaukhahi~uquatrongplasma,ngaycakhi m~tdQcaobonm~tdQMottkha nhieu.Dieu naydant& sv tangcuO'ngexcitonicm~nhva taihqpexcitonicvan conchiemUtithea nhfingm~tdQcao(traingu<Jcv& band~nkhoivaQW a m~t dQtuongduong). 3) Vi hi~uUngChIDyeti,hi~uUnglapd~ythonggianphatranenqUailtrQng,d~c bi~tavilngnhi~tdQthap.Hi~uUnglapd~ythong gianphag~yra mQtky di t~i mvcFermitrongph6quanghQc.Sov& h~bandankhoivaQW,ky di naysac bonvaphvthuQcm~ bonVaGnhi~tdQ. -"""" 53