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1.3μm自组织InGaAs/InAs/GaAs量子点激光器分子束外延生长

2021-05-08 来源:帮我找美食网
维普资讯 http://www.cqvip.com 第27卷第3期 半导体学报 Vo1.27 No.3 Mar..2006 2006年3月 CHINESE JOURNAL OF SEMIC0NDUCT0lRS 1.3IJLm InGaAs/InAs/GaAs Self-Assembled Quantum Dot Laser Diode Grownby Molecular Beam Epitaxy .Niu Zhichuan ,Ni Haiqia0,Fang Zhidan,Gong Zheng,Zhang Shiy0ng,Wu D0nghai, Sun Zheng,Zha0 Huan,Peng H0ngling,Han Qin,and Wu R0nghan (Institute of Semiconductors,Chinese Academy of Sciences,Beijing 100083,China) Abstract:The growth of multi 1ayer InGaAs/InAs/GaAs self-assembled quantum dots(QDs)by molecular beam epitaxy(MBE)is investigated,and a QD laser diode lasing at l_33“m in continuous operation mode at room tem- perature is reported.The full width at half maximum of the band edge emitting peaks of the photoluminescence (PL)spectra at room temperature is less than 35meV for most of the multi.1ayer QD samples,revealing good。re- producible MBE growth conditions.Moreover,atomic force microscopy images show that the QD surface density can be controlled in the range from 1 x 10 0 to 7 x 10 0 cm .The best PL properties are obtained at a QD surface density of about 4 x 10 。cm .Edge emitting lasers containing 3 and 5 stacked QD layers as the active layer lasing at room temperature in continuous wave operation mode are reported. Key words:quantum dot;InAs;laser diode PACC;7320D;7280E;7820 CLC number!TN304.054 Document code:A Article ID:0253-4177(2006)03-0482-07 InAs QDs can be tuned in the 1.1~1.7“m region 1 Intr0duction by varying the growth conditions 。。.Many high quality InAs QD lasers with low threshold current InAs quantum dots(QDs)have been inten— density and high characteristic temperature have sively studied in recent years because of their been reportedEl . promising applications in 1.3“m QD lasers for fi— Although significant improvements in the ber—optic communication systems.InAs QD lasers growth of InAs Q・Ds have been achieved,optical are expected to have superior lasing properties, gain is still limited by relatively low dot density. such as a low threshold current density and a high which makes InAs QD lasers hard to lase at the characteristic temperature,because of their delta— ground state.There are two main effective ways function—like density of statesL¨.Thus.they are a to overcome this problem:one is to increase the promising alternative to commercial InGaAsP— QD density by optimising the growth conditions, based lasers,which have poor temperature charac— and the other is to increase the effective number teristics because of insufficient carrier localization of QDs by using multi—layer QD structures.The in their q uantum wells.In addition,using GaAs InAs QD density has been increased to about 1 x substrate for the InAs QDs would make it possible 10 0~1 x 10n cm一 bv varying growth condi. to use AlGaAs alloys as cladding and waveguide tions[ ~ ’ .However,at a high QD density,the layers and fabricate an AIGaAs/GaAs Bra g re QD size is small,and the emitting wavelength flector in a single process at low cost. tends to be shortC ~ Ⅲ].In this paper.we present a In the past few years,much work has been detailed study of the growth conditions of InAs done to improve and exploit the properties of self- QDs by MBE.Relatively long emit ting wave- assembled InAs QDs grown by molecular beam lengths of 1.33~1.35 m with a high density up epitaxy(MBE)[ ~ .The emission wavelength of to 4 x 10 0cm~are achieved. *Project supported by the National Natural Science Foundation of China。the National High Technology Research and Development Program of China,and the State Key Development Program for Basic Research of China t Corresponding author.Email:zcniu@red.semi.ac.cn Received 31 October 2005,revised manuscript received 9 December 2005 @2006 Chinese Institute of Electronics 维普资讯 http://www.cqvip.com 第3期 Niu Zhichuan et a1.:1.3gm InGaAs/InAs/GaAs Self-Assembled Quantum Dot Laser Diode Grown…483 Multi—layer structures are usually adopted to increase optical gain for QD laser devices[ 卜 引. However.the coupled QDs in the multi.1ayer structures are usually highly strained.In this work,thick GaAs spacer layers up to 50nm be— tween the QD layers are adopted.We also take an in situ annealing treatment during the growth of the spacer layers to remove defects induced by the high stress.In addition,we have focused exten— sively on reducing the defects inside the QDs and narrowing the dot size distribution while keeping the density high.The density of the InAs QDs is increased,and the optical properties are improved by optimising growth conditions.InGaAs cap lay- ers are employed to extend the wavelength of the InAs QDs to 1.35“m.High-performance InAs QD edge—emitting lasers lasing at room temperature in continuous wave operation mode are reported. 2 Experiment The InAs QDs were grown on(001)GaAs substrate in a Veeco Mod GenⅡMBE system e. quipped with a reflection high--energy electron—- diffraction(RHEED)instrument.The epitaxial structures contain a 300nm GaAs buffer layer,a QD active region,a 50nm GaAs capping layer,and a QD layer on top。which is for atomic force mi- croscopy(AFM)measurement.The QD active re- gion was formed by depositing 1.8~3.5 mono— layer(ML)InAs followed by a thin InGaAs COV— ering layer.The InAs QDs were formed under a repeated growth sequence of a 0.1~0.15ML InAs growth(1~5s)and a 5s As exposure,which is known as the interruption growth mode.The growth interruption was introduced in order for the substrate to reach thermal equilibrium at the desired QD growth temperature.The growth tem- peratures were 580℃for the buffer and 460~ 510℃for the QDs and covering layers.A valved As cracker cell was used to supply the As2 beam. The As/ⅢBEP ratio for all the layers was kept between 15 and 20.The transition of InAs growth mode from two to three dimensions was checked by the RHEED. For laser structures,the QD active region is grown at the center of an undoped GaAs waveguide with n-type lower and P-type upper cladding layers of Al0 5Ga0 5As.The Be and Si do— ping level in the n--and P--type cladding layers is 2 x 10 。cm~.Device fabrication begins with the formation of 20um ridges with reactive ion etch— ing followed by the plasma..enhanced chemica1..va.. por deposition of a thin SiO2 layer.The SiO2 layer above the ridge is plasma.etched to enable electri— cal contact.The CrAu P—type contacts are e.beam deposited.Finally,Au.Ge—Ni n—type contacts are e.beam deposited after the substrate has been lapped down to a thickness of about 125pm.The wafer is then cleaved into laser bars with a cavity length of 3mm,without facet coating. The variable temperature PL spectra were measured using the 632.8nm line of a He—Ne laser and dispersed using a Nicolet FTI R760 Fourier spectrometer.The signal was collected using a cooled Ge detector.The AFM measurements were carried out to study the QD morphology using a NanoScapeⅢa(Digital Instruments)microscope in contact mode. 3 Results and discussion 3.1 control of the morphology of the InAs QDs The AFM images of InAs QDs of samples 1A,1B,1C,1D,1E,and 1F are shown in Fig.1. The QDs were formed using the interruption mode at 480℃.The InAs deposition amounts for samples 1A~1F were 1.8。2.2,2.5,3.0,3.0,and 2.2ML。respectively.The InAs deposition rate was 0.1ML/s for samples 1A,1B,1C,1D,and 1F and O.15ML/s for sample 1E.The lnAs QDs were formed under a repeated growth sequence of a O.1ML InAs growth(1s)and a 5s As exposure for samples 1A~1E and a sequence of a 0.5ML InAs growth(5s)and a 5s As exposure for the sample 1F.For all samples.when 1.8~2.0ML was depo— sited,the RHEED pattern changed from streaky to spotty—indicating that lnAs grows in a 3D mode.From the AFM images,it is clear that the QD density increases gradually to a maximum as the amount of InAs deposition increases.But fur— ther increasing the InAs deposition could decrease the QD density.For the sample 1A,the amount of InAs deposition lies iust at the critical thickness for dot formation.Its QD density is only 7.I x 100 cm .The QD density increases to about 4.2 x 10 0 cm一 when the amount of InAs deposition in— 维普资讯 http://www.cqvip.com 484 半导体学报 第27卷 Fig.1 AFM images(a)~(f)of InAs QDs of samples 1A~1F grown by MBE on GaAs(001)substrate (1 m×1 m area for all images) creases to 2.5ML.This high density is favorable for increasing the gain to make the InAs QD la— sers lase at the ground state.The average QD di. ameter and the height of samples 1A,1B。and 1C are similar,about 45 and 4.5nm,respectively.The distribution of their ODs size is narrow.But the QDs of sample 1D are of bimodal distribution. The average lateral diameter of the large QlDs is about 51.3nm,and the height is about 10nm.The average lateral diameter of the small QDs is about 25nm,and the height is about 5nm.For samples 1A,1B,and 1C,the QD density increases with InAs deposition while the average QD size actua1. IY remains constant.This is a little different from the phenomenon observed by LeonardL ‘ and KobayashiL 引,in which with InAs deposition,the average QD size decreases while the QD density increases,which has been explained in terms of the interaction between QDs and an attachment barrier around the QD edges.The explanation for our case could be that the interaction between the QDs and the attachment barrier around the QD edges prevents the QDs from growing up but is not strong enough to reduce the QD size.As more InAs is deposited,the size distribution of the QDs evolves into a bimodal distribution while the QD density decreases,which is just the case of sample 1D.The reason for this could be that the neigh. bouring QDs begin to coalesce to reduce the QD density as more InAs is deposited.As a conse. quence,the effect of the QD interactions is re. duced,resulting in an increase in the average size of existing the QDs and formation of new,small QDs.The formation of this bimodal distribution indicates the coexistence of two metastable states and strongly supports the thermodynamic nature of the quantum dot growthE .Malachias has shown using X.ray diffraction that the small nanostructures are coherent(strained)and the large nanostructures are incoherent(relaxed)[193. Since the bimodal distribution and incoherent structure are not favourable for QD lasers,they should be restrained during the growth. The growth conditions of sample 1E are simi. 1ar to 1D except for a higher growth rate of 0.15ML/s.In the AFM image of sample 1E,the bimodal distribution is not obvious.The density of the small QlDs is low and the size of the large QDs is small compared to sample 1D.This means that a high growth rate could restrain the evolution of the bimodal distribution.A high growth rate could also increase the QD density.As a consequence, the amount of InAs deposition for sample 1E is not enough for the neighbouring QDs to coalesce as in sample 1D. The amount of InAs deposition per pulse in the interruption mode also affects the morphology of the QDs.Sample 1F was grown in a sequence of a 0.5ML InAs growth(5s)and a 5s As exposure. Its other growth parameters are the same as that of sample 1B.Ftom AFM images.it is clear that its QD density,2.59×1010cm~。is a lightly higher than that of sample 1B.which is 2.15×10 0cm~. Another important growth parameter for InAs QDs is temperature.It is known that the QD den. sity could be increased noticeably by lowering the growth temperature.However,the low tempera. ture could induce defects and poor optical proper. ties,effects which will be discussed later. 3.2 Photoluminescence properties of the InAs QDs PL spectra for samples 1A~1F are shown in Fig.2.The InAs QDs of samples 1B~1F are COV- ered with 6nm In0 2 Ga0 8As,but sample 1A is capped by GaAs directly.From the above mot. phology studies,the QD size of sample 1A is simi・ lar to samples 1B,1C,1E,and 1F.But its emitting wavelength is noticeably shorter than the latter ones.This means that the QDs emit at a longer wavelength when the In0 2 Ga0 8 As cover layer partially reduces the compressive stress and lowers the potential barriers. The low QD density is subject to saturation of the ground state when excited intensely.Thus the 维普资讯 http://www.cqvip.com 第3期 Niu Zhichuan et a1.:1.3#m InGaAs/lnAs/GaAs Self-Assembled Quantum Dot Laser Diode Grown…485 = 匕 曼 J 口_ 一 J Wavelength/nm Fig.2 PL spectra of samples 1A,1B,1C,and 1D(a), and 1E and 1 F(b)at room temperature with an exci- tation power of 16mW relative intensity of the emitting peak from the first excited state is inversely proportional to the QD density when excited with intense light.This is consistent with our case.From Fig.2,it is clear that the relative peak intensity of the first excited state decreases as the QD density increases for samples 1A,1B,1D,and 1C.The peak intensity of the first excited state is even higher than the ground state for sample 1A.due to its very low QD density.For sample 1 C,the peak of the first excited state is hard to recognize due to its very high QD density,which is very favourable for la— ser devices. Figure 2 shows that the peak intensity of sample 1B is much higher than that of sample 1A. This could be explained by the different QD den- sities and covering layers between the samples. For the sample with a higher QD density,more QDs contribute to emission when excited with the same intensity.In addition,the I no 2 Gao 8 As cov- ering layer could relax the compressive stress of the QDs partially and reduce the formation of the non—radiative defects.As a consequence,the emis— sion intensity of sample 1B should be stronger than that of sample 1A.However,the emission of samples with even higher QD density,such as 1C, 1D.and 1E,is lower than that of sample 1B.This can be explained by the greater number of non..ra.. diative defects formed during the OD growth due to the large compressive stress induced by the higher QD density.The growth conditions of sam— ple 1F are almost the same as that of sample 1B except for the amount of the I nAs deposition per interruption.But Figure 2(b)shows that its emis— sion is much shorter than sample 1 B.A possible explanation for this could be that the substrate could not reach thermal equilibrium during the continuous deposition of the I nAs in this case.The amount of I nAs deposition per interruption also affects the PL pro—perties.As shown in Fig.2(b), sample 1E shows a slight blue shift compared to the sample 1D due to the larger amount of InAs deposition per interruption. The temperature dependence of the PL emis— sion of sample 1C was investigated under the exci— tation power of 16mW from 8.3 to 300K,as shown in Fig.3.TO better illustrate the PL prop— erties,we plot the temperature dependencies of the peak position,intensity,and FWHM of the low energy peak in Figs.3(b)~(c).Up to 80K, the energy peak position shifts to a low energy mOnOtOnicallv.At about 100 K.an anomalous de. crease was observed.We explain this behaviour as being caused by a thermally activated electron transfer from the small dots to the larger ones. The temperature dependence of the FWHM of the peak better illustrates this behaviour,as shown in Fig.3(c).We observe an anomalous decrease of the FWHM around 100K due to the thermally ac— tivated electron transfer. In many previous reports・S—type curves were observed in the temperature dependent PL spectra of the InAs QDs ~纠.The S—type curve at Iow temperatures iS usually related to the high carrier localization inside the QDs.It is hard to observe the S.type curve in Fig.3.This indicates that the density of the carrier localization inside the QDs in sample 1 C is low,revealing a good MBE growth condition. 3.3 Properties of the InAs QD edge emitting lasers From the above discussion,we know.that sample 1C has a high QD density and good PL 维普资讯 http://www.cqvip.com 486 半导体学报 第27卷 芦 扫一兽善一一 国 1llJ0Z Photon energy/eV Temperature/K Temperature/K Fig.3 Temperature dependent PL spectra of sample 1C with an excitation power of 16roW (a)Normal- ized intensity;(b)Peak position;(C)Integration in tensity and FWHM of the low energy peak properties for laser devices.Although the QD den- sity has been increased to 4.2×10 0 cm~for sam— pie 1C,it iS still too lOW for the InAs QD lasers to lase at the ground state.We overcome this prob- lem by increasing the effective number of QDs using multi.1ayer QD structures.Five layers of InAs oDs were grown with 50nm GaAs layers as barriers.The GaAs barriers are thick enough to decouple the neighbouring QD layers.The barriers were annealed during growth to eliminate non,-ra—. diative defects. Figure 4(a)shows the laser spectrum of an InAs QD 1aser with a 3mm-long cavity in continu— OUS wave mode at room temperature.The lasing wavelength iS 1.33t ̄m,confirming that the device lases at the ground state.Our wavelength iS com. parable to the best reported RT CW quantum dot laser at 1.33 um with a much lower threshold cur. rent density of 19A/cm0[2l_.Figure 4(b)shows the light output characteristics and bias voltage versus current of the laser.The threshold current and threshold current density are about l50 mA and 250A/cm .respectively.The average external dif- ferential quantum efficiency,仇xI,can be extracted from the slope of the L-I curve.The value iS a- bout 21.6%.The results >Q量、indi cate t事 hat the structure of the multi..1ayer of ODs separated by the an.. nealed GaAs spacer layers prevents gain satura- tion,allowing US to achieve a long-wavelength la- ser operating at the ground state. 之 彗 享王 Q事 _ 曼 ∞ .. 1’; Current intensity/A Fig.4 (a)Laser spectrum of a 3mm—cavity—length InAs QD laser operating in C W mode measured at room temperature:(b)Light output characteristics and bias voltage versus current of the lasers 4 Conclusion We have successfully grown multi--layer In-- GaAs/InAs/GaAs self-assembled quantum dot la— ser diodes emitting at 1.3tzm.The morphology and surface density of the InAs QDs can be controlled by the MBE growth parameters.The QD layer, 维普资讯 http://www.cqvip.com 第3期 Niu Zhichuan et a1.:1.3“m InGaAs/InAs/GaAs Self-Assembled Quantum Dot Laser Diode Grown…487 with a surface density of around(3~4)x 10 cm~,shows good PL properties.The effects Of QD morphology on PL properties are discussed; no S—type curve appeared in the temperature de- pendent PL spectra(from 8.3 to 300K),indica. ting that the density of the carrier localization in. side the QDs is low.The edge emitting lasers contai. ning 5 layers of QDs and lasing at room temperature in continuous wave operation mode are achieved. References [1] Qiu Y,Gogna P,Forouhar S.High-performance InAs quan- tum-dot lasers near 1.3um.Appl Phys Lett,2001,79:3570 [2] Wang X D,Niu Z C・Feng S L・et a1.Passive mode-locking in 1.3um two-section InAs quantum dot lasers.J Cryst Growth,2001,223:363 [3] Niu Z C。Wang X D。Miao Z。et a1.Modification of emission wavelength of self.assembled InGaAs/GaAs quantum dots covered bv InGaAs layer.J Cryst Growth,2001,227:1062 [4] Gong Z,Fang Z D,Xu X H・et a1.Role of different cap lay- ers tuning the wavelength of self-assembled InAs/GaAs quantum dots.J Phys:Condens Matter,2003,15:5383 [5] Fang Z D,Gong Z,Miao Z H,et a1.Effect of the InAlAs and InGaAs combination strain.reducing layer on 1.3um e. mission self.assembled InAs/GaAs quantum dots.J Phys D Appl Phys,2004,37:1012 [6] Ma B S,Wang X D,Su F U,et a1.Photoluminescence from self-assembled long-wavelength InAs/GaAs quantum dots under pressure.J Appl Phys,2004,95:933 [7] Niu Zhichuan,Han Qin,Ni Haiqiao,et a1.Material growth and device fabrication of GaAs based 1.3um GaInNAs quan- tum well laser diodes.Chinese Journal of Semiconductors, 2005。26(19):1860 [8] Safar G A M。Rodrigues W N,Cury L A,et a1.Effect of Te as a surfactant on the optical properties of InAs self-assem- bled quantum dots.Appl Phys Lett,1997,71:521 [9] Brusaferri L,Sanguinetti S,Grillj E,et a1.Thermally activa- ted carrier transfer and lumineseenee lineshape in self.organ- ized InAs quantum dots.Appl Phys Lett。1996,69:3354 El0] Mukai K.Ohtsuka N,Suguwara M.et a1.Self.formed InGaAs quantum dots on GaAs substrates emitting at 1.3um.Jpn J Appl Phys,1994,33:L1710 [11] Ustinov V M,Zhukov A E,Maleev N A,et a1.1 3um InAs/ GaAs quantum dot lasers and VCSELs grown by molecular beam epitaxy.J Cryst Growth,2001,227/228:1155 [123 Tatebayashi J,Hatori N,Ishida M,et a1.1.28um lasing from stacked InAs/GaAs quantum dots with low.temperature. grown AIGaAs cladding layer by metalorganic chemical va- por deposition.Appl Phys Lett,2005,86:053107 [13] Nuntawong N,Xin Y C,Birudavolu S,et a1.Quantum dot la- sers based on a stacked and strain.compensated active region grown by metal-organic chemical vapor deposition.Appl Phys Lett,2005,86:193115 [14] Tabebayashi J.Arakawa Y.Hatori N,et a1.InAs/GaAs self. assembled quantum--dot lasers grown by metalorganic chemi-- cal vapor deposition-effects of postgrowth annealing on stacked InAs quantum dots.Appl Phys Lett,2004,85:1024 [15] Liu H Y,Sellers I R,Gutierrez M,et a1.Influence of the spacer layer growth temperature on multilayer InAs/GaAs quantum dot structures.Appl Phys Lett,2004,96:1988 [16] Park G,SHchekin O B,Huffaker D L,et a1.Low.th reshold oxide.confined 1.3um quantum.dot laser.IEEE Photonics Technol Lett,2000,12:227 [17] Mirin R P。Ibbetson J P,Nishi K,et a1.1.3um photolumines- cence from InGaAs quantum dots on GaAs.Appl Phys Lett, 1995。67:3795 [18] Eliseev P G。Stintz H。Li A,et a1.Transition dipole moment of lnAs/InGaAs quantum dots from experiments on ul- tralow.threshold laser diodes.Appl Phys Lett,2000,77:262 [19] Leonard D。Pond K,Petroff P M.C rjtical layer thickness for self assembled InAs islands on GaAs Phys Rev B.1994,5O: 11687 [2O] Kobayashi N P.Ramachandran T R,Chen P,et a1.In-situ,a・ tomic force microscope studies of the evolution of InAs three.dimensional islands on GaAs(001).Appl Phys Lett。 1996,68:3299 [21] Malachias A,Neves B R A,Rodrigues W N,et a1.X-ray scat- tering from self.assembled InAs islands.Brazilian Journal of Physics,2004,34(2B):571 F22] Lubyshev D I.Gonzalez.Borrero P P。Marcga E,et a1.Exci- tation localization and temperature stability in self-organized InAs quantum dots.Appl Phys Lett・1996,68:205 [23] Kissel H.Muller U。Walther C,et a1.Size distribution in self- assembled InAs quantum dots on GaAs(001)for intermedi- ate InAs coverage.Phys Rev B,2000,62:7213 维普资讯 http://www.cqvip.com 488 半导体学报 第27卷 1.3pLm自组织InGaAs/InAs/GaAs量子点激光器分子束外延生长 牛智川 倪海桥 方志丹 龚 政 张石勇 吴东海 孙 征 赵 欢 彭红玲 韩 勤 吴荣汉 (中国科学院半导体研究所,北京 100083) 摘要:报道了分子束外延生长的1.3 m多层InGaAs/lnAs/G|dAs自组织量子点及其室温连续激射激光器.室温 带边发射峰的半高宽小于35meV,表明量子点大小比较均匀.原子力显微镜图像显示,量子点密度可以控制在(1~ 7)×10 cm 范围之内,而面密度处于4×10 cm 时有良好的光致发光谱性能.含有三到五层1.3 m量子点的 激光器成功实现了室温连续激射. 关键词:量子点;砷化铟;激光器 PACC:7320D;7280E;7820 中图分类号:TN304.054 文献标识码:A 文章编号:0253—4177(2006)03—0482—07 *国家自然科学基金,国家高技术发展研究计划及国家再点基础研究发展计划资助项f=1 十通信作者Email;zcniu@red.semi.tic.crl 2005—10-31收到.2005-12-09定稿 @2006中同电子学会 

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