SEMICONDUCTOR MATERIALS

Evaluation of four inch diameter VGF-Ge substrates used for manufacturing multi-junction solar cell

Kewei Cao, Tong Liu, Jingming Liu, Hui Xie, Dongyan Tao, Youwen Zhao, Zhiyuan Dong and Feng Hui

+ Author Affiliations

 Corresponding author: Kewei Cao, Email: caokewei@semi.ac.cn

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Abstract: Low dislocation density Ge wafers grown by a vertical gradient freeze (VGF) method used for the fabrication of multi-junction photovoltaic cells (MJC) have been studied by a whole wafer scale measurement of the lattice parameter, X-ray rocking curves, etch pit density (EPD), impurities concentration, minority carrier lifetime and residual stress. Impurity content in the VGF-Ge wafers, including that of B, is quite low although B2O3 encapsulation is used in the growth process. An obvious difference exists across the whole wafer regarding the distribution of etch pit density, lattice parameter, full width at half maximum (FWHM) of the X-ray rocking curve and residual stress measured by Raman spectra. These are in contrast to a reference Ge substrate wafer grown by the Cz method. The influence of the VGF-Ge substrate on the performance of the MJC is analyzed and evaluated by a comparison of the statistical results of cell parameters.

Key words: crystallitiesX-ray diffractionsemiconducting germaniumsemiconducting gallium arsenidesolar cells



[1]
Bett A W, Dimroth F, Stollwerck G, et al. Ⅲ-Ⅴ compounds for solar cell applications. Appl Phys A,1999, 69:119
[2]
Avrutin V, Izyumskaya N, Morkoç H, et al. Semiconductor solar cells:recent progress in terrestrial applications. Superlattices Microstruc, 2011, 49:337
[3]
Law D D, King R R, Yoon H, et al. Future technology pathways of terrestrial Ⅲ-Ⅴ multijunction solar cells for concentrator photovoltaic systems. Sol Energy Mater Sol Cells, 2010, 94:1314
[4]
Aiken D, Dons E, Je S S, et al. Lattice-matched solar cells with 40% average efficiency in pilot production and a roadmap to 50%. IEEE J Photovolt, 2013, 3:1
[5]
Luque A. Will we exceed 50% efficiency in photovoltaics. J Appl Phys, 2011, 110:031301
[6]
Green M A, Emery K, Hishikawa Y, et al. Solar cell efficiency tables (version 40). Prog Photovolt, 2012, 20:606
[7]
Fetzer C M,Yoon H, King R R, et al. 1.6/1.1 eV metamorphic GaInP/GaInAs solar cells grown by MOVPE on Ge. J Cryst Growth, 2005, 276:48
[8]
Liu X Q, Fetzer C M, Rehder E, et al. Organometallic vapor phase epitaxy growth of upright metamorphic multijunction solar cells. J Cryst Growth, 2012, 352:186
[9]
Surek T. Crystal growth and materials research in photovoltaics:progress and challenges. J Cryst Growth, 2004, 10:93
[10]
Taishi T, Ise H, Murao Y, et al. Oxygen doped Ge crystals Czochralski-grown from the B2O3-fully-covered melt. Microelectron Eng, 2011, 88:496
[11]
Taishi T, Ise H, Murao Y, et al. Czochralski-growth of germanium crystals containing high concentrations of oxygen impurities. J Cryst Growth, 2010, 312:2783
[12]
Frank-Rotsch CH, Rudolph P. Vertical gradient freeze of 4 inch Ge crystals in a heater-magnet module. J Cryst Growth, 2009, 311:2294
[13]
Langheinrich D, Pätzold O, Raabe L, et al. VGF growth of germanium single crystals without crucible contact. J Cryst Growth, 2010, 312:2291
[14]
Qu Xiaosheng, Zhang Sisi, Bao Hongyin, et al. The effect of InAs quantum-dot size and interdot distance on GaInP/GaAs/GaInAs/Ge multi-junction tandem solar cells. Journal of Semiconductors, 2013, 34(6):062003
[15]
Bellmann M P, Pätzold O, Stelter M, et al. Optimisation of the VGF growth process by inverse modelling. J Cryst Growth, 2010, 312:2175
[16]
Ignacio R S, Enrique B, Beatriz G, et al. Analysis of germanium epiready wafers for Ⅲ-Ⅴ heteroepitaxy. J Cryst Growth, 2008, 310:4803
[17]
Jin Chaohua. Numerical study of heat transport and fluid flow during the silicon crystal growth process by the Czochralski method. Journal of Semiconductors, 2013, 34(6):063005
[18]
Cooper A S. Precise lattice constants of germanium, aluminium, gallium arsenide, uranium, sulphur, quartz and sapphire. Acta Cryst, 1962, 15:578
[19]
Pinto S R C, Rolo A G, Chahboun A, et al. Raman study of stress effect on Ge nanocrystals embedded in Al2O3. Thin Solid Films, 2010, 518:5378
[20]
Nishioka T, Shinoda Y, Ohmachi Y. Raman microprobe analysis of stress in Ge and GaAs/Ge on SiO2 coated Si substrates. J Appl Phys,1985, 57:276
[21]
Yamaguchi M. Fundamentals and R&D status of Ⅲ-Ⅴ compound solar cells and materials. Phys Status Solidi C, 2015, 6:489
[22]
Yamaguchi M, Amano C. Efficiency calculations of thin film GaAs solar cells on Si substrates. J Appl Phys, 1985, 58:3601
Fig. 1.  (Color online) Micrographs from two samples and reference wafer after preferential etching, (a)-(c) are belong to sample A, (d)-(f) for reference wafer, (g)-(I) for sample B.

Fig. 2.  Radial distribution of carrier concentration of the Ge wafer along the whole diameter scale. The horizontal axis is the distance to the center of the wafer. Inset: the mean concentration of each sample is added and the error bars show the standard deviation of three samples.

Fig. 3.  (Color online) XRD rocking curves for (a) sample A, (b) reference wafer, and (c) sample B. Four points in each sample were characterized and signed 1-4 in each figure. The fourth figure shows the positions measured on each wafer.

Fig. 4.  (Color online) Raman spectra of two samples with the fitting result in the right side.

Table 1.   Impurity content in Ge wafers (in ppm wt).

B, Ag, V, Co, Cu<0.005<0.005
Ti, Cr, Ni, Pt<0.01<0.01
Mn, Mo, Fe<0.5<0.5
Au<0.1<0.1
Ga0.891.9
DownLoad: CSV

Table 2.   Bragg angle and lattice parameter.

SampleAB
Bragg angle (°)33.01833.013
Lattice parameter (Å)5.65445.6551
DownLoad: CSV

Table 3.   FWHM of two samples.

SampleAB
FWHM(arcsec)160.3237.54
253.4351.16
3202.894.47
420.2293.54
DownLoad: CSV

Table 4.   The peak shift, linewidth, calculated stress of three samples.

Sample A B
Peak shift (cm-1) 0.09 0.23
Linewidth (cm-1) 3.94 3.64
Stress (109 dyne/cm2) 0.306 0.782
DownLoad: CSV

Table 5.   The performance of the MJC manufactured on each sample.

SampleAB Reference
Voc (mV)2525.4-2528.42629.4-2631.72633.4-2636.7
Isc (mA)197.4-198.6201.3-202.1203.4-203.8
Vmp (mV)2240.7-2248.52292.9-2293.32284.2-2284.3
Imp (mA)188.4-191.8194.2-196.1197.2-198.7
η (100%)26.01-26.5627.44-27.6927.74-27.96
FF0.847-0.8590.841-0.8460.841-0.845
DownLoad: CSV
[1]
Bett A W, Dimroth F, Stollwerck G, et al. Ⅲ-Ⅴ compounds for solar cell applications. Appl Phys A,1999, 69:119
[2]
Avrutin V, Izyumskaya N, Morkoç H, et al. Semiconductor solar cells:recent progress in terrestrial applications. Superlattices Microstruc, 2011, 49:337
[3]
Law D D, King R R, Yoon H, et al. Future technology pathways of terrestrial Ⅲ-Ⅴ multijunction solar cells for concentrator photovoltaic systems. Sol Energy Mater Sol Cells, 2010, 94:1314
[4]
Aiken D, Dons E, Je S S, et al. Lattice-matched solar cells with 40% average efficiency in pilot production and a roadmap to 50%. IEEE J Photovolt, 2013, 3:1
[5]
Luque A. Will we exceed 50% efficiency in photovoltaics. J Appl Phys, 2011, 110:031301
[6]
Green M A, Emery K, Hishikawa Y, et al. Solar cell efficiency tables (version 40). Prog Photovolt, 2012, 20:606
[7]
Fetzer C M,Yoon H, King R R, et al. 1.6/1.1 eV metamorphic GaInP/GaInAs solar cells grown by MOVPE on Ge. J Cryst Growth, 2005, 276:48
[8]
Liu X Q, Fetzer C M, Rehder E, et al. Organometallic vapor phase epitaxy growth of upright metamorphic multijunction solar cells. J Cryst Growth, 2012, 352:186
[9]
Surek T. Crystal growth and materials research in photovoltaics:progress and challenges. J Cryst Growth, 2004, 10:93
[10]
Taishi T, Ise H, Murao Y, et al. Oxygen doped Ge crystals Czochralski-grown from the B2O3-fully-covered melt. Microelectron Eng, 2011, 88:496
[11]
Taishi T, Ise H, Murao Y, et al. Czochralski-growth of germanium crystals containing high concentrations of oxygen impurities. J Cryst Growth, 2010, 312:2783
[12]
Frank-Rotsch CH, Rudolph P. Vertical gradient freeze of 4 inch Ge crystals in a heater-magnet module. J Cryst Growth, 2009, 311:2294
[13]
Langheinrich D, Pätzold O, Raabe L, et al. VGF growth of germanium single crystals without crucible contact. J Cryst Growth, 2010, 312:2291
[14]
Qu Xiaosheng, Zhang Sisi, Bao Hongyin, et al. The effect of InAs quantum-dot size and interdot distance on GaInP/GaAs/GaInAs/Ge multi-junction tandem solar cells. Journal of Semiconductors, 2013, 34(6):062003
[15]
Bellmann M P, Pätzold O, Stelter M, et al. Optimisation of the VGF growth process by inverse modelling. J Cryst Growth, 2010, 312:2175
[16]
Ignacio R S, Enrique B, Beatriz G, et al. Analysis of germanium epiready wafers for Ⅲ-Ⅴ heteroepitaxy. J Cryst Growth, 2008, 310:4803
[17]
Jin Chaohua. Numerical study of heat transport and fluid flow during the silicon crystal growth process by the Czochralski method. Journal of Semiconductors, 2013, 34(6):063005
[18]
Cooper A S. Precise lattice constants of germanium, aluminium, gallium arsenide, uranium, sulphur, quartz and sapphire. Acta Cryst, 1962, 15:578
[19]
Pinto S R C, Rolo A G, Chahboun A, et al. Raman study of stress effect on Ge nanocrystals embedded in Al2O3. Thin Solid Films, 2010, 518:5378
[20]
Nishioka T, Shinoda Y, Ohmachi Y. Raman microprobe analysis of stress in Ge and GaAs/Ge on SiO2 coated Si substrates. J Appl Phys,1985, 57:276
[21]
Yamaguchi M. Fundamentals and R&D status of Ⅲ-Ⅴ compound solar cells and materials. Phys Status Solidi C, 2015, 6:489
[22]
Yamaguchi M, Amano C. Efficiency calculations of thin film GaAs solar cells on Si substrates. J Appl Phys, 1985, 58:3601
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    Received: 15 October 2015 Revised: 10 November 2015 Online: Published: 01 June 2016

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      Kewei Cao, Tong Liu, Jingming Liu, Hui Xie, Dongyan Tao, Youwen Zhao, Zhiyuan Dong, Feng Hui. Evaluation of four inch diameter VGF-Ge substrates used for manufacturing multi-junction solar cell[J]. Journal of Semiconductors, 2016, 37(6): 063002. doi: 10.1088/1674-4926/37/6/063002 K W Cao, T Liu, J M Liu, H Xie, D Y Tao, Y W Zhao, Z Y Dong, F Hui. Evaluation of four inch diameter VGF-Ge substrates used for manufacturing multi-junction solar cell[J]. J. Semicond., 2016, 37(6): 063002. doi: 10.1088/1674-4926/37/6/063002.Export: BibTex EndNote
      Citation:
      Kewei Cao, Tong Liu, Jingming Liu, Hui Xie, Dongyan Tao, Youwen Zhao, Zhiyuan Dong, Feng Hui. Evaluation of four inch diameter VGF-Ge substrates used for manufacturing multi-junction solar cell[J]. Journal of Semiconductors, 2016, 37(6): 063002. doi: 10.1088/1674-4926/37/6/063002

      K W Cao, T Liu, J M Liu, H Xie, D Y Tao, Y W Zhao, Z Y Dong, F Hui. Evaluation of four inch diameter VGF-Ge substrates used for manufacturing multi-junction solar cell[J]. J. Semicond., 2016, 37(6): 063002. doi: 10.1088/1674-4926/37/6/063002.
      Export: BibTex EndNote

      Evaluation of four inch diameter VGF-Ge substrates used for manufacturing multi-junction solar cell

      doi: 10.1088/1674-4926/37/6/063002
      Funds:

      the National Natural Science Foundation of China No. 61474104

      Project supported by the National Natural Science Foundation of China (No. 61474104).

      More Information
      • Corresponding author: Email: caokewei@semi.ac.cn
      • Received Date: 2015-10-15
      • Revised Date: 2015-11-10
      • Published Date: 2016-06-01

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