光抽运太赫兹探测技术研究ZnSe的光致载流子动力学特性
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摘要
利用光抽运-太赫兹探测技术,研究了ZnSe的载流子弛豫过程和太赫兹波段电导率的时间演化过程.在中心波长为400 nm的抽运光作用下,ZnSe的载流子弛豫过程用双指数函数进行了很好的拟合,其快的载流子弛豫时间和慢的载流子弛豫时间均随抽运光密度的增加而增大.快的载流子弛豫时间随抽运光密度的增加而增大与样品中的缺陷有关,随着激发光密度的增加,激发的光生载流子浓度增大,缺陷逐渐被光生载流子填满,致使快的载流子弛豫时间增大;慢的载流子弛豫时间随着抽运光密度增加而增大主要和带填充有关.不同抽运光延迟时间下ZnSe在太赫兹波段的瞬态电导率用Drude-Smith模型进行了很好的拟合.对ZnSe光致载流子动力学特性的研究为高速光电器件的设计和制造提供了重要的实验依据.
Optical pump-terahertz(THz) probe spectroscopy is employed to investigate the photo-excited carrier relaxation process and the evolution of terahertz conductivity in Zn Se.With the pump pulse at a wavelength of 400 nm,the carrier relaxation process can be well fitted to a biexponential function.We find that the recombination process in Zn Se occurs through two components,one is the fast carrier recombination process,and the other is the slow recombination process.The fast carrier relaxation time constant is in a range from a few tens of picoseconds to hundreds of picoseconds,and slow carrier relaxation time constant ranges from one to several nanoseconds.We find that both the fast and the slow carrier relaxation time constant increase with the power density of pump beam increasing,which is related to the density of defects in the sample.Upon increasing the excitation power density,the defects are filled by the increased photo-excited carriers,which leads to an increase in the fast carrier relaxation time.While,the slow carrier relaxation time increasing with pump flux can be attributed to the filling of surface state.We also present the THz complex conductivity spectra of Zn Se at different delay times with a pump flux of 240 μJ/cm2.It is shown that the real part of the conductivity decreases with increasing the pump-probe delay time.The real part of the conductivity is positive and increases with frequency in each of the selective three delay times(2,20,and 100 ps),while the imaginary part is negative and decreases with frequency.The transient conductivity spectra at terahertz frequency in different delay times are fitted with Drude-Smith model.According to the fitting results from Drude-Smith model,with the pump-probe delay time increasing,the average collision time τ and the value of c_1 decrease.Generally,a higher carrier density leads to a more frequent carrier-carrier collision,which means that the collision time should decrease with carrier density increasing.The abnormal carrier density dependence of collision time implies a predominance of backscattering in our Zn Se.The predominance of backscattering is also observed for the negative value of c_1.The negative value of c_1 indicates that some photocarriers are backscattered in Zn Se.With a delay time of 2 ps,the value of c_1 approaches to-1,which indicates that the direct current(DC) conductivity is suppressed,and the maximum conductivity shifts toward higher frequency.With increasing the delay time,the value of c_1decreases:in this case DC conductivity dominates the spectrum.The study of the dynamics of photoinduced carriers in Zn Se provides an important experimental basis for designing and manufacturing the high speed optoelectronic devices.
Optical pump-terahertz(THz) probe spectroscopy is employed to investigate the photo-excited carrier relaxation process and the evolution of terahertz conductivity in Zn Se.With the pump pulse at a wavelength of 400 nm,the carrier relaxation process can be well fitted to a biexponential function.We find that the recombination process in Zn Se occurs through two components,one is the fast carrier recombination process,and the other is the slow recombination process.The fast carrier relaxation time constant is in a range from a few tens of picoseconds to hundreds of picoseconds,and slow carrier relaxation time constant ranges from one to several nanoseconds.We find that both the fast and the slow carrier relaxation time constant increase with the power density of pump beam increasing,which is related to the density of defects in the sample.Upon increasing the excitation power density,the defects are filled by the increased photo-excited carriers,which leads to an increase in the fast carrier relaxation time.While,the slow carrier relaxation time increasing with pump flux can be attributed to the filling of surface state.We also present the THz complex conductivity spectra of Zn Se at different delay times with a pump flux of 240 μJ/cm2.It is shown that the real part of the conductivity decreases with increasing the pump-probe delay time.The real part of the conductivity is positive and increases with frequency in each of the selective three delay times(2,20,and 100 ps),while the imaginary part is negative and decreases with frequency.The transient conductivity spectra at terahertz frequency in different delay times are fitted with Drude-Smith model.According to the fitting results from Drude-Smith model,with the pump-probe delay time increasing,the average collision time τ and the value of c_1 decrease.Generally,a higher carrier density leads to a more frequent carrier-carrier collision,which means that the collision time should decrease with carrier density increasing.The abnormal carrier density dependence of collision time implies a predominance of backscattering in our Zn Se.The predominance of backscattering is also observed for the negative value of c_1.The negative value of c_1 indicates that some photocarriers are backscattered in Zn Se.With a delay time of 2 ps,the value of c_1 approaches to-1,which indicates that the direct current(DC) conductivity is suppressed,and the maximum conductivity shifts toward higher frequency.With increasing the delay time,the value of c_1decreases:in this case DC conductivity dominates the spectrum.The study of the dynamics of photoinduced carriers in Zn Se provides an important experimental basis for designing and manufacturing the high speed optoelectronic devices.
引文
[1]Shah J 1996 Ultrafast Spectroscopy of Semiconductors and Semiconductor Nanostructures(New York:Springer)p132
[2]Othonos A 1998 J.Appl.Phys.83 1789
[3]Ulbricht R,Hendry E,Shan J,Heinz T F,Bonn M 2011Rev.Mod.Phys.83 543
[4]Li M,Wu B,Ekahana S A,Utama M I B,Xing G,Xiong Q,Sum T C,Zhang X 2012 Appl.Phys.Lett.101 091104
[5]Parkinson P,Dodson C,Joyce H J,Bertness K A,Sanford N A,Herz L M,Johnston B M 2012 Nano Lett.124600
[6]Li G,Xue X,Lin X,Yuan S,Tang N,Chu F,Cui H,Ma G 2014 Appl.Phys.A 116 45
[7]Dakovski G L,Kubera B,Lan S,Shan J 2006 J.Opt.Soc.Am.B 23 139
[8]Liu H,Lu J,Hao F T,Li D,Feng Y P,Tang S H,Chorng H S,Zhang X 2012 J.Phys.Chem.C 116 26036
[9]Larsen C,Cooke G D,Jepsen P U 2011 J.Opt.Soc.Am.B 28 1308
[10]Park H,Kim W R,Jeong H T,Lee J J,Kim H G,Choi W Y 2011 Sol.Energ.Mat.Sol.C 95 184
[11]Liu H,Lu J,Zheng M,Chorng H S 2013 Nano Res.6808
[12]Xue X,Jiang M,Li G,Lin X,Ma G,Jin P 2013 J.Appl.Phys.114 193506
[13]Tsokkou D,Othonos A,Zervos M 2012 Appl.Phys.Lett.100 133101
[14]Haripadmam P C,John H,Philip R,Gopinath P 2014Appl.Phys.Lett.105 221102
[15]Kong D G,Ao G H,Gao Y C,Chang Q,Wu W Z,Ran L L,Ye H 2012 Physica B 407 4251
[16]Yao G X,LüL H,Gui M F,Zhang X Y,Zheng X F,Ji X H,Zhang H,Cui Z F 2012 Chin.Phys.B 21 107801
[17]Ku S A,Tu C M,Chu W C,Luo C W,Wu K H,Yabushita A,Chi C C,Kobayashi T 2013 Opt.Express21 13930
[18]LüZ,Zhang D,Zhou Z,Sun L,Zhao Z,Yuan J 2012Appl.Opt.51 676
[19]Ropagnol X,Morandotti R,Ozaki T,Reid M 2011 IEEEPhoton.J.3 174
[20]He S,Chen X,Wu X,Wang G,Zhao F J 2008 J.Lightwave Technol.26 1519
[21]Xu X L,Wang X M,Li F L,Zhang X C,Wang L 2004Spectrosc.Spect.Anal.24 1153[徐新龙,王秀敏,李福利,张希成,汪力2004光谱学与光谱分析24 1153]
[22]Han J G,Abul K A,Zhang W L J 2007 J.Nanoelectron.Optoelectron.2 222
[23]Zhang X C,Jin Y,Ma X F 1992 Appl.Phys.Lett.612764
[24]Wu Q,Zhang X C 1995 Appl.Phys.Lett.67 3523
[25]Sosnowski T S,Norris T B,Wang H H,Grenier P,Whitaker J F,Sung C Y 1997 Appl.Phys.Lett.70 3245
[26]Joseph S M,Prashant V K 2014 Nat.Photon.8 737
[27]Price M B,Butkus J,Jellicoe T C,Sadhanala A,Briane A,Halpert J E,Bronch K,Hodgkiss M J,Friend H R,Deschler F 2015 Nat.Commun.6 8420
[28]Hegmann F A,Ostroverkhova O,Cooke D G 2006 Photophysics of Molecular Materials(Weinheim:WileyVCH Press)p367
[29]Palik 1998 Handbook of Optical Constants of Solids(Vol.2)(Chestnut Hill:Academic Press)p752
[30]Titova V L,Cocker L T,Cooke G D,Wang X Y,Meldrum A,Hegmann A F 2011 Phys.Rev.B 83 085403
[2]Othonos A 1998 J.Appl.Phys.83 1789
[3]Ulbricht R,Hendry E,Shan J,Heinz T F,Bonn M 2011Rev.Mod.Phys.83 543
[4]Li M,Wu B,Ekahana S A,Utama M I B,Xing G,Xiong Q,Sum T C,Zhang X 2012 Appl.Phys.Lett.101 091104
[5]Parkinson P,Dodson C,Joyce H J,Bertness K A,Sanford N A,Herz L M,Johnston B M 2012 Nano Lett.124600
[6]Li G,Xue X,Lin X,Yuan S,Tang N,Chu F,Cui H,Ma G 2014 Appl.Phys.A 116 45
[7]Dakovski G L,Kubera B,Lan S,Shan J 2006 J.Opt.Soc.Am.B 23 139
[8]Liu H,Lu J,Hao F T,Li D,Feng Y P,Tang S H,Chorng H S,Zhang X 2012 J.Phys.Chem.C 116 26036
[9]Larsen C,Cooke G D,Jepsen P U 2011 J.Opt.Soc.Am.B 28 1308
[10]Park H,Kim W R,Jeong H T,Lee J J,Kim H G,Choi W Y 2011 Sol.Energ.Mat.Sol.C 95 184
[11]Liu H,Lu J,Zheng M,Chorng H S 2013 Nano Res.6808
[12]Xue X,Jiang M,Li G,Lin X,Ma G,Jin P 2013 J.Appl.Phys.114 193506
[13]Tsokkou D,Othonos A,Zervos M 2012 Appl.Phys.Lett.100 133101
[14]Haripadmam P C,John H,Philip R,Gopinath P 2014Appl.Phys.Lett.105 221102
[15]Kong D G,Ao G H,Gao Y C,Chang Q,Wu W Z,Ran L L,Ye H 2012 Physica B 407 4251
[16]Yao G X,LüL H,Gui M F,Zhang X Y,Zheng X F,Ji X H,Zhang H,Cui Z F 2012 Chin.Phys.B 21 107801
[17]Ku S A,Tu C M,Chu W C,Luo C W,Wu K H,Yabushita A,Chi C C,Kobayashi T 2013 Opt.Express21 13930
[18]LüZ,Zhang D,Zhou Z,Sun L,Zhao Z,Yuan J 2012Appl.Opt.51 676
[19]Ropagnol X,Morandotti R,Ozaki T,Reid M 2011 IEEEPhoton.J.3 174
[20]He S,Chen X,Wu X,Wang G,Zhao F J 2008 J.Lightwave Technol.26 1519
[21]Xu X L,Wang X M,Li F L,Zhang X C,Wang L 2004Spectrosc.Spect.Anal.24 1153[徐新龙,王秀敏,李福利,张希成,汪力2004光谱学与光谱分析24 1153]
[22]Han J G,Abul K A,Zhang W L J 2007 J.Nanoelectron.Optoelectron.2 222
[23]Zhang X C,Jin Y,Ma X F 1992 Appl.Phys.Lett.612764
[24]Wu Q,Zhang X C 1995 Appl.Phys.Lett.67 3523
[25]Sosnowski T S,Norris T B,Wang H H,Grenier P,Whitaker J F,Sung C Y 1997 Appl.Phys.Lett.70 3245
[26]Joseph S M,Prashant V K 2014 Nat.Photon.8 737
[27]Price M B,Butkus J,Jellicoe T C,Sadhanala A,Briane A,Halpert J E,Bronch K,Hodgkiss M J,Friend H R,Deschler F 2015 Nat.Commun.6 8420
[28]Hegmann F A,Ostroverkhova O,Cooke D G 2006 Photophysics of Molecular Materials(Weinheim:WileyVCH Press)p367
[29]Palik 1998 Handbook of Optical Constants of Solids(Vol.2)(Chestnut Hill:Academic Press)p752
[30]Titova V L,Cocker L T,Cooke G D,Wang X Y,Meldrum A,Hegmann A F 2011 Phys.Rev.B 83 085403