J. Semicond. > Volume 36 > Issue 9 > Article Number: 093001

Extraction of the defect density of states in microcrystalline silicon from experimental results and simulation studies

T. Tibermacine 1, , A. Merazga 2, , M. Ledra 1, and N. Ouhabab 1,

+ Author Affiliations + Find other works by these authors

PDF

Abstract: The constant photocurrent method in the ac-mode (ac-CPM) is used to determine the defect density of states (DOS) in hydrogenated microcrystalline silicon (μc-Si:H) prepared by very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD). The absorption coefficient spectrum (ac-α ()), is measured under ac-CPM conditions at 60 Hz. The measured ac-α () is converted by the CPM spectroscopy into a DOS distribution covering a portion in the lower energy range of occupied states. We have found that the density of valence band-tail states falls exponentially towards the gap with a typical band-tail width of 63 meV. Independently, computer simulations of the ac-CPM are developed using a DOS model that is consistent with the measured ac-α () in the present work and a previously measured transient photocurrent (TPC) for the same material. The DOS distribution model suggested by the measurements in the lower and in the upper part of the energy-gap, as well as by the numerical modelling in the middle part of the energy-gap, coincide reasonably well with the real DOS distribution in hydrogenated microcrystalline silicon because the computed ac-α () is found to agree satisfactorily with the measured ac-α ().

Key words: constant photocurrent methodoptical absorption spectrummicro-crystalline silicondefect density of states

Abstract: The constant photocurrent method in the ac-mode (ac-CPM) is used to determine the defect density of states (DOS) in hydrogenated microcrystalline silicon (μc-Si:H) prepared by very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD). The absorption coefficient spectrum (ac-α ()), is measured under ac-CPM conditions at 60 Hz. The measured ac-α () is converted by the CPM spectroscopy into a DOS distribution covering a portion in the lower energy range of occupied states. We have found that the density of valence band-tail states falls exponentially towards the gap with a typical band-tail width of 63 meV. Independently, computer simulations of the ac-CPM are developed using a DOS model that is consistent with the measured ac-α () in the present work and a previously measured transient photocurrent (TPC) for the same material. The DOS distribution model suggested by the measurements in the lower and in the upper part of the energy-gap, as well as by the numerical modelling in the middle part of the energy-gap, coincide reasonably well with the real DOS distribution in hydrogenated microcrystalline silicon because the computed ac-α () is found to agree satisfactorily with the measured ac-α ().

Key words: constant photocurrent methodoptical absorption spectrummicro-crystalline silicondefect density of states



References:

[1]

Chen S H, Chang T W, Wang H W. Quality evaluation for microcrystalline silicon thin-film solar cells by single-layer absorption[J]. International Journal of Photoenergy, 2012.

[2]

Chen S H, Wang H W, Chang T W. Absorption coefficient modeling of microcrystalline silicon thin film using Maxwell-Garnett effective medium theory[J]. Opt Express, 2012, 20(6): A197.

[3]

Kocka J, Fejfar A, Mates T. The physics and technological aspects of the transition from amorphous to microcrystalline and polycrystalline silicon[J]. Phys Status Solidi C, 2004, 1(5): 1097.

[4]

Larbi F, Belfedal A, Sib J. Density of states in intrinsic and n/p-doped hydrogenated amorphous and microcrystalline silicon[J]. J Modern Phys, 2011, 2: 1030.

[5]

Vanecek M, Kocka J, Poruba A. Direct measurement of the deep defect density in thin amorphous silicon films with the absolute constant photocurrent method[J]. J Appl Phys, 1995, 78(10): 6203.

[6]

Fejfar A, Poruba A, Vanecek M. Precise measurement of the deep defects and surface states in a-Si:H films by absolute CPM[J]. J Non-Crystalline Solids, 1996, 198(200): 304.

[7]

Jackson W B, Amer N M, Boccara A C. Photothermal deflection spectroscopy and detection[J]. Appl Opt, 1981, 20(8): 1333.

[8]

Lee S, Kumar S, Wronski C. A critical investigation of a-Si:H photoconductivity generated by subgap absorption of light[J]. J Non Crystalline Solids, 1989, 114: 316.

[9]

Brüggemann R. Numerical modelling of transient photoconductivity for density of states determination in microcrystalline silicon[J]. Phys Status Solidi C, 2004, 1(5): 1227.

[10]

Pierz K, Hilgenberg B, Mell H. Gap-state distribution in N-type and P-type a-Si:H from optical absorption[J]. J Non-Crystalline Solids, 1987, 97(98): 63.

[11]

Reynolds S, Smirnov V, Main C. Transient photocurrents in microcrystalline silicon films[J]. Proceedings of Materials Research Society, 2002: 715.

[12]

Brammer, Stiebig. Defect density and recombination lifetime in microcrystalline silicon absorbers of highly efficient thin-film solar cells determined by numerical device simulations[J]. J Appl Phys, 2003, 94(2): 1035.

[13]

Meaudre M, Meaudre R, Vignoli S. Density of states in hydrogenated microcrystalline silicon determined by space charge limited current[J]. J Non-Crystalline Solids, 2002, 299(302): 626.

[14]

Hattori K, Musa Y, Murakami N. Photocarrier transport in undoped microcrystalline silicon studied by the modulated photocurrent technique[J]. J Appl Phys, 2003, 94(8): 5071.

[15]

Reynolds S. Carrier mobility, band tails and defects in microcrystalline silicon[J]. J Phys: Conference Series, 2010, 253: 012002.

[16]

Ritter D, Weiser K. Suppression of interference fringes in absorption measurements on thin films[J]. Opt Commun, 1986, 57(5): 336.

[17]

Schmidt J A, Rubinelli F A. Limitations of the constant photocurrent method: a comprehensive experimental and modeling study[J]. J Appl Phys, 1998, 83(1): 339.

[1]

Chen S H, Chang T W, Wang H W. Quality evaluation for microcrystalline silicon thin-film solar cells by single-layer absorption[J]. International Journal of Photoenergy, 2012.

[2]

Chen S H, Wang H W, Chang T W. Absorption coefficient modeling of microcrystalline silicon thin film using Maxwell-Garnett effective medium theory[J]. Opt Express, 2012, 20(6): A197.

[3]

Kocka J, Fejfar A, Mates T. The physics and technological aspects of the transition from amorphous to microcrystalline and polycrystalline silicon[J]. Phys Status Solidi C, 2004, 1(5): 1097.

[4]

Larbi F, Belfedal A, Sib J. Density of states in intrinsic and n/p-doped hydrogenated amorphous and microcrystalline silicon[J]. J Modern Phys, 2011, 2: 1030.

[5]

Vanecek M, Kocka J, Poruba A. Direct measurement of the deep defect density in thin amorphous silicon films with the absolute constant photocurrent method[J]. J Appl Phys, 1995, 78(10): 6203.

[6]

Fejfar A, Poruba A, Vanecek M. Precise measurement of the deep defects and surface states in a-Si:H films by absolute CPM[J]. J Non-Crystalline Solids, 1996, 198(200): 304.

[7]

Jackson W B, Amer N M, Boccara A C. Photothermal deflection spectroscopy and detection[J]. Appl Opt, 1981, 20(8): 1333.

[8]

Lee S, Kumar S, Wronski C. A critical investigation of a-Si:H photoconductivity generated by subgap absorption of light[J]. J Non Crystalline Solids, 1989, 114: 316.

[9]

Brüggemann R. Numerical modelling of transient photoconductivity for density of states determination in microcrystalline silicon[J]. Phys Status Solidi C, 2004, 1(5): 1227.

[10]

Pierz K, Hilgenberg B, Mell H. Gap-state distribution in N-type and P-type a-Si:H from optical absorption[J]. J Non-Crystalline Solids, 1987, 97(98): 63.

[11]

Reynolds S, Smirnov V, Main C. Transient photocurrents in microcrystalline silicon films[J]. Proceedings of Materials Research Society, 2002: 715.

[12]

Brammer, Stiebig. Defect density and recombination lifetime in microcrystalline silicon absorbers of highly efficient thin-film solar cells determined by numerical device simulations[J]. J Appl Phys, 2003, 94(2): 1035.

[13]

Meaudre M, Meaudre R, Vignoli S. Density of states in hydrogenated microcrystalline silicon determined by space charge limited current[J]. J Non-Crystalline Solids, 2002, 299(302): 626.

[14]

Hattori K, Musa Y, Murakami N. Photocarrier transport in undoped microcrystalline silicon studied by the modulated photocurrent technique[J]. J Appl Phys, 2003, 94(8): 5071.

[15]

Reynolds S. Carrier mobility, band tails and defects in microcrystalline silicon[J]. J Phys: Conference Series, 2010, 253: 012002.

[16]

Ritter D, Weiser K. Suppression of interference fringes in absorption measurements on thin films[J]. Opt Commun, 1986, 57(5): 336.

[17]

Schmidt J A, Rubinelli F A. Limitations of the constant photocurrent method: a comprehensive experimental and modeling study[J]. J Appl Phys, 1998, 83(1): 339.

Search

Advanced Search >>

GET CITATION

T. Tibermacine, A. Merazga, M. Ledra, N. Ouhabab. Extraction of the defect density of states in microcrystalline silicon from experimental results and simulation studies[J]. J. Semicond., 2015, 36(9): 093001. doi: 10.1088/1674-4926/36/9/093001.

Export: BibTex EndNote

Article Metrics

Article views: 1238 Times PDF downloads: 10 Times Cited by: 0 Times

History

Manuscript received: 19 January 2015 Manuscript revised: Online: Published: 01 September 2015

Email This Article

User name:
Email:*请输入正确邮箱
Code:*验证码错误