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Zinc telluride, due to its direct band gap and broadband light absorption, has the good application prospects in terahertz devices, solar cells, waveguide devices, and green light emitting diodes. In the photovoltaic field, it is possible to further improve the photoelectron conversion efficiency of multi-junction tandem solar cells by combining zinc telluride with III-V semiconductors. Ultrafast photo-excited carrier dynamics is fundamental to understand photoelectron conversion process of nanofilm solar cells. In this study, the ultrafast energy carrier dynamics of N-doped polycrystalline zinc telluride is investigated by using the femtosecond laser two-color pump-probe method at room temperature. The polycrystalline zinc telluride nanofilm is grown on a 500 μm GaAs (001) substrate via molecular beam epitaxy and doped by using a nitrogen ratio frequency plasma cell. The laser pulses with a central wavelength of 800 nm are divided into pump beam and probe beam by a beam splitter, after which the pump beam passes through a bismuth triborate crystal and its frequency is doubled to 400 nm. The 400 nm pump beam and 800 nm probe beam are focused on the sample collinearly through the same objective lens. Photo-excited carriers will be generated since the excitation photon energy of 400 nm pump beam (3.1 eV) is higher than the band gap of zinc telluride (～ 2.39 eV). The experimental data are analyzed by using the theoretical fitting model which includes energy relaxation processes of electrons and lattice, and the theoretical curves are consistent well with the experimental data. The fitted results show that the three dominated relaxation processes which affect the initial reflectivity recovery are in sub-picosecond time regime. The positive amplitude electron relaxation process is attributed to inter-band carrier cooling and carrier diffusion through electron-photon interactions, and the deduced decay time of this positive amplitude electron relaxation process is about 0.75 ps. The negative amplitude electron relaxation process is characterized as a photo-generated carrier trapping process induced by defects, and the decay time of this process is about 0.61 ps. The lattice heating process is realized through electron-phonon coupling process, and the calculated time constant of the lattice heating is about 0.86 ps.
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Keywords:
- zinc telluride /
- polycrystalline /
- femtosecond laser /
- carrier
[1] Guo Q X, Kume Y, Fukuhara Y, Tanaka T, Nishio M, Ogawa H, Hiratsuka M, Tani M, Hangyo M 2007 Solid State Commun. 141 188
[2] Chang J H, Takai T, Godo K, Song J S, Koo B H, Hanada T, Yao T 2002 Phys. Status Solidi (b) 229 995
[3] Wu S N, Ding D, Johnson S R, Yu S Q, Zhang Y H 2010 Prog. Photovolt. 18 328
[4] Xia Z L, Fan Z X, Shao J D 2006 Acta Phys. Sin. 55 3007 (in Chinese) [夏志林, 范正修, 邵建达 2006 55 3007]
[5] Wang H D, Ma W G, Guo Z Y, Zhang X, Wang W 2011 Chin. Phys. B 20 040701
[6] Collier C M, Holzman J F 2014 Appl. Phys. Lett. 104 042101
[7] Qi J, Chen X, Yu W, Cadden-Zimansky P, Smirnov D, Tolk N H, Miotkowski I, Cao H, Chen Y P, Wu Y, Qiao S, Jiang Z 2010 Appl. Phys. Lett. 97 182102
[8] Jia L, Ma W G, Zhang X 2014 Appl. Phys. Lett. 104 241911
[9] Wu A Q, Xu X F 2007 Appl. Phys. Lett. 90 251111
[10] Zhu J, Tang D W, Wang W, Liu J, Holub K W, Yang R G 2010 J. Appl. Phys. 108 094315
[11] Ma W G, Wang H D, Zhang X, Wang W 2011 Acta Phys. Sin. 60 064401 (in Chinese) [马维刚, 王海东, 张兴, 王玮 2011 60 064401]
[12] Zhu L D, Sun F Y, Zhu J, Tang D W 2012 Acta Phys. Sin. 61 130512 (in Chinese) [朱丽丹, 孙方远, 祝捷, 唐大伟 2012 61 130512]
[13] Norris P M, Caffrey A P, Stevens R J, Michael Klopf J, Mcleskey Jr J T, Smith A N 2003 Rev. Sci. Instrum. 74 400
[14] Hopkins P E, Stewart D A 2009 J. Appl. Phys. 106 053512
[15] Rast S, Schneider M L, Onellion M, Zeng X H, Si W D, Xi X X, Abrecht M, Ariosa D, Pavuna D, Ren Y H, Lpke G, Perakis I 2001 Phys. Rev. B 64 214505
[16] Wright O B, Gusev V E 1995 Appl. Phys. Lett. 66 1190
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[1] Guo Q X, Kume Y, Fukuhara Y, Tanaka T, Nishio M, Ogawa H, Hiratsuka M, Tani M, Hangyo M 2007 Solid State Commun. 141 188
[2] Chang J H, Takai T, Godo K, Song J S, Koo B H, Hanada T, Yao T 2002 Phys. Status Solidi (b) 229 995
[3] Wu S N, Ding D, Johnson S R, Yu S Q, Zhang Y H 2010 Prog. Photovolt. 18 328
[4] Xia Z L, Fan Z X, Shao J D 2006 Acta Phys. Sin. 55 3007 (in Chinese) [夏志林, 范正修, 邵建达 2006 55 3007]
[5] Wang H D, Ma W G, Guo Z Y, Zhang X, Wang W 2011 Chin. Phys. B 20 040701
[6] Collier C M, Holzman J F 2014 Appl. Phys. Lett. 104 042101
[7] Qi J, Chen X, Yu W, Cadden-Zimansky P, Smirnov D, Tolk N H, Miotkowski I, Cao H, Chen Y P, Wu Y, Qiao S, Jiang Z 2010 Appl. Phys. Lett. 97 182102
[8] Jia L, Ma W G, Zhang X 2014 Appl. Phys. Lett. 104 241911
[9] Wu A Q, Xu X F 2007 Appl. Phys. Lett. 90 251111
[10] Zhu J, Tang D W, Wang W, Liu J, Holub K W, Yang R G 2010 J. Appl. Phys. 108 094315
[11] Ma W G, Wang H D, Zhang X, Wang W 2011 Acta Phys. Sin. 60 064401 (in Chinese) [马维刚, 王海东, 张兴, 王玮 2011 60 064401]
[12] Zhu L D, Sun F Y, Zhu J, Tang D W 2012 Acta Phys. Sin. 61 130512 (in Chinese) [朱丽丹, 孙方远, 祝捷, 唐大伟 2012 61 130512]
[13] Norris P M, Caffrey A P, Stevens R J, Michael Klopf J, Mcleskey Jr J T, Smith A N 2003 Rev. Sci. Instrum. 74 400
[14] Hopkins P E, Stewart D A 2009 J. Appl. Phys. 106 053512
[15] Rast S, Schneider M L, Onellion M, Zeng X H, Si W D, Xi X X, Abrecht M, Ariosa D, Pavuna D, Ren Y H, Lpke G, Perakis I 2001 Phys. Rev. B 64 214505
[16] Wright O B, Gusev V E 1995 Appl. Phys. Lett. 66 1190
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