第23卷第6期 半导体学报 Vo1.23,No.6 2002年6月 CHINESE JOURNAL OF SEMICONDUCTORS June,2002 Tunnel Junction AIGaInP Light Emitting Diode Wang Guohong ,Shen Guangdi .Guo Xia .Gao Guo .Wet Xin ,Zhang Guangze。 Ma Xiaoyu .Li Yuzhang and then Lianghui。 t、j mf of]*afo ̄ati.n・13e ̄iingPo6 technifUM… y andBeaTingOptoelectrom ̄TechvologyImbogagor)-.BeOiag、00022 r L ̄ma) (2 institute of … “c} .The Chinese Acad ̄y of Sciences,13come l00083.China) Abstract:The n type GaAs substrates are used and their conductive type is changed to P type by tunnel】unction for AIGalnP light emitting diodes(TJ—I ED),then n type GaP layer is used as current spreading layer.Because resistiv itv of the n type GaP is lower than that of P type—the e ̄feet of current spreading layer is enhanced and the light ex— traction efficiency is increased by the n type GaP current spreading layer.For TJ LED with 3Fm n—type GaP cur— rent spreading layer,experimental results show that compared with conventional LED with p-type GaP current spreading layer.1ight output power is increased for 50 at 20mA and f0r 66.7%at 100mA. Key words:tunnel Junction:A1GalnP:high brightness LED:MOCVD PACC:4255P;4260D;6865:7230 CLC number:TN312 .8 Document code:A Artiele ID}0253 4l77(2002)06 0628—04 ode and reverse biased pn junction current block— 1 Introduction ing layer or native oxide AlAs current blocking layer ’ .But these methods lead to higher COSt or High brightness visible light emitting diodes make fabrication process more difficult.Another (LEDs)are becoming increasingly important and way is using n-type GaP or A1GaAs as current have numerous applications,such as in the field of spreading layer with p——type GaAs suhstrate be—— optical display.traffic signal and automobile cause n-type GaP or A1GaAs current spreading lamp c 。 with different aluminum composition.The layer’s conductivity is better than that of p—type. quaternary A1GalnP alloys,which can be precisely But P type GaAs substrate has severa1 disadvan 1att[ce matched to GaAs substrate,have a direct rages 1[sted below. bandgap ranged from 1.88 to 2.30eV .Mass pro (1)Doping leve1 of low resistivity substrate is ducfion of AIGaInP high brightness LEDs has been very high,for example:1×10 em .Conventiona1 realized by using multi——wafers metal organic—-them—- dopant is Zn,then diffusion of Zn during the ep[ ica1 vapor deposition(MOCVD)system.One proh一 taxy wil1 destroy the heterostructure interface.es 1em of the A1GaInP LEDs is the restriction of light peeially for quantum wel1 structure.Reducing it s extraction efficiency caused by light absorption of doping level will increase the serial resistance of top anode because current injection concentrates device. under anode.Ivlany methods were considered to re— (2)Quality of commercial P type OaAs sub duce the current jnjeetion under anode t such as strate is not as good as n—type GaAs st]bstrate. thick current spreading layer ,transparent an (3)Price is higher than n—type substrate. Wang Guohoag mMe s burn Ln 1964.PhD.He is engaged in the research on material growth by MOCVD/or Light emitting diodes and 【aser diodes Received 29 September 2001,revised maauscript received 9 November 2001 维普资讯 http://www.cqvip.com
6期 Wang Guohong et al:Tunnel Junction AIGalnP Light Emitting Diode 629 Semiconductor tunnel iunctions have been widely researched口一and used in semiconductor de GaP current spreading layer.The traditional LEDs were also fabricated with same DH structure and p-type GaP current spreading layer,but without vices- .In this article n 一GaAs/p一 GaAs tun nel junction was grown on n GaAs substrate.Then P—type(A1。7Gac 3)。5In0 P can be used on the p GaAs layer for lower current confinement layer.So the original n—type GaAs substrate worked as P— type substrate.In sequence n GaP current spread inglayer could be used onthetop ofthe P——i——n dou-- tunne1 junction. 3 Material growth and device fabri— cation AIGaInP materials were grown on GaAs sub ble heterojunction active layer to enhance the effect of current spreading.The tunnel junction was re versely biased and worked as a resistance when the p i n double heterou儿1cti0n active layer was for wardly biased. 2 Structure of device For the sake of comparing the difference be tween the effect of n—type current spreading layer and p-type current spreading layer,we use simple double heter0junction(DH)active layer and GaP current spreading layer with same thickness for both TJ—I ED and conventional LED. The schematic cross sectiona1 structure of TJ— LED is shown in Fig.1.The epilayers were grown by MOCVD on n GaAs substrate.In sequence the ^_ Ge i anode n ̄g,aPeu ̄nt spreadinghyerO ̄m) Ⅱ_fA c jIn corai ̄rnem e m' ——i-AIGmhtPactive 5 Ⅲ) n_ As 【些‰ : 一 Ⅱ_ As sub日lr| /mGeNi calI Fig.1 Schematic structure of tunnel junction At GalnP lJED device consists of 0.2Hm n—GaAs buffer layer,n GaAs(20nm)/p GaAs(1 5nm)tunneling junc tion,DH structure with 1 m P一(A1 0 7Ga。3)c=In¨P 1ower confinement 1ayer,0.5 m i(AI—Ga ) 一 Ino P 1ight emitting layer and 1 m n一(AI。 Ga¨)。 In。、P upper confinement layer,and 3 m n—type strate with orientation(001)toward(111)A off 1j。by AXITRON AIX 200 MOCVD system.TM Ga,TMA1,and TMIn were used as groupⅢele— ments precursors.PH3 and AsH3 were used as group V elements precursors.For A1GaInP materi al growth,the ratio of V/Ⅲwas 100.DEZn and SiHd were used as dopants sources for p-type and n type,respectively.The growth temperature of epilayer was 70O~750℃.The total flow rate of hy drogen was 7 L/rain. For GaAs tunne1 iunction,Si was used as the n type dopant with doping level reaching 5×l0 cm。,and C was used as p-type dopant with doping level of 1×10a0cm。.n type GaP current spreading layers were doped with Si.The doping level reached 2×1 0 cm。.p-type GaP current spreading layers were doped with Zn.The doping level reached 4×l0 cm。.The resistivlties of GaP cur rent spreading 1ayers were 0.020・cm and 0.05 0・cm for n—type and p-type respectively(Hall measurement results). Au/Zn/Au was used as p-type contacts.  ̄100,um round top anode was formed by lithogra phy.AuGeNi was used as n—type contacts.The wafer was sawn to square dices of 300 ̄m×300 ̄m bounded on copper heat sinks for measurement. 4 Device properties and discussion Light output power and operation voltage of the two kinds of LED were measured by HT semi— conductor laser measurement system,which was calibrated at the visible light region.Figure 2 shows the results of measurement.The output 维普资讯 http://www.cqvip.com
630 半导体学报 23卷 light power of TJ—LED reached 0.42mW at 20mA, which is Increased for 50 more than that of LED current of LED with p-type current spreading layer will crowd under the top anode,the injection cur— rent will create more heat,and current crowding under anode increases the light emitting region car— rler mj’ectlon level which will cause more carriers leak from light emitting layer to confinement lay— r. without tunnel unction.And at 100mA the OUtput light power of TJ—I ED reached 2-0row increased for 66.7 .It can be seen from Fig.2 that the de— vice saturation current with n type GaP current 唱Id 吣 spreading layer was increased.Because the injection 0 1 一/ , , 0 , , r / , / r / , , 唔ld , / lima 吣 0 .,。 , ltmA Fig.2 Output power and operation voltage versus injertion current of the AIGalnP 620nm LED without(a)and with tunnel junction(b) Figure 2 also shows that the operating voltage TJ I EDs with 3Ⅲn n—type GaP current spreading layer,experimental results show that the light Out of the TJ—LED is slightly higher than that of LED without tunnel junction at the same injection cur— rent.This is caused by two factors,the tunnel;unc— tion reverse operation voltage,and the n type GaP put power was increased for 50 at 20mA and for 66.7 at 100mA of conventional LED with p-type GaP current spreading layer. ohmic contact resistance.Because n—type GaP doped with Si can not reach very high doping level, the top n—type ohmic contact resistance is larger than that of heavily doped P—-type GaP ohmic con—— [1]Wang Guohong,Ma Xiaoyu.Cao Qing,et a1.AIGalnP high brightness orange 1 ht emitting diodes manufactured by LP Referenees tsct.But the operating voltage of TJ—I ED is around 2.4V at 20mA.This is acceptable for prac— tical application. M0CVD Chia ̄e IournaI of Semiconduetors.1998,19:712 (in Chinese)[王国宏,马骁宇.曹青,等.LP—MOCVD制备 AiGalnP高亮度橙黄色发光二极替.半导体学报,1998.19: 71z] 5 Conclusion Tunnel junction AIGalnP light emitting diodes (TJ LED)with n—type GaAs substrate and n—type GaP current spreading layer were successfully fab— ricated.The effect of current spreading layer was enhanced and the light extraction efficiency was in— creased by n—type GaP current spreading layer.For [2] I u Dacheng,Han Peide,Liu Xiangl[n,et a1.GaInN/AIGaN double heretojunctlon grin tlght emitting diede ̄.Chh ̄se of Semiconductors,2000,21:414[陆大成.韩堵德.刘样林.等. GalnN/AIGaN腰异质结绿光发光二搔管.半导体学报, 2000,21:414] [3]Chi G C.Su Y K,Jou M J.et a1.Window layer for current spre*ding in InGaA1P light—emkting diode.J App[Phys, 1994,76(5):1 [4 Lia J F,WuM C,】0uM J,et a1.Highly reliable operation of 维普资讯 http://www.cqvip.com
6期 Wang Guohong a1.}Tunnel Junction A1GaInP Light Emitting Diode 631 [ndion2 tin oxide AIGaInP orange light—emittign diodes Elee一 [7: Esaki I.Discovery of the tunnd diode IEEE Trans El…t Dn tron Lett.1094,30(21):1793 Devices,l976,ED 23 664 [9] Sugawara H,haya Kt Hatakoshi G.Hybrid type InGaAIP/ [8] Chung B C.Virshup G F,Klausmeier Bro M et I_25 2 GaAs dis ̄ibuted bragg re[1ectors for InGaAIP iight emitting efficiency<1… r mas3 0)AIGaAs/GaAs/InGaAsP diodes Jpn』Appl Phys,1994,33:61 95 three junction twe ̄termina[solar cell AppI Phys Lett,1992, [5]Huang K H,Yu J G.Yu』G,et aI.Twofold efficiency im 60(14) 1601 provement in high performance AIGalnP[ight emitting :0] Guo Xia,Shen Guangdi,Wang Guohong,et ai.Tunnel regen— diodes in the j65~690nm spetrai region USing thick GaP erated muhipie active—region light—emitting diodes with high window layer.Appi Phys Lettt1992,61f9):31 efficiency.Appl Phys[Att,2001,79f18):2986 隧道结AIGalnP发光二极管 王国宏。 沈光地 郭 霞 高 国 韦 欣 张广泽 马骁宇 李玉璋 陈良惠 (1北京工业大学信息学院北京市光电子技术实验室,北京 100022) (2中国科学院半导体研究所,北京100083) 摘要:报道了通过隧道结将衬底的导电类型从n型转变到P型,从而可以利用n型GaP作为以n型GaAs为衬底 的A1GaInP发光二极管的电流扩展层.n型电流扩展层的电阻率低于P型电流扩展层的电阻率,这种结构改善了 电流扩展层的作用,从而提高了发光二极昔的光提取效率.对3fierGaP电流扩展层的发光二极昔,实验结果表明, 隧道结发光二极昔的发光功率与具有相同基本结构的传统发光二极昔相比,20mA时发光功率提高了5O , 100mA时提高了66.7 . 美键词:隧道结;AIGaInPI高亮度发光二极管 M0CVD PACC}4255P{4260D{6865;7230 中圈分类号:TN31 2 .8 文献标识码:A 文章编号:0253 41 77(2002)06 0628 04 王目宏男,1964年出生,博士,主要从事半导体发光二极管和激光器材料的MOCkeD生长技术的研究. 鲫01 09 20收到,2001 11 09定稿 @2002中国电子学会
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