Fabrication and Analysis of InGaAsN-based Solar Cells Grown by MOVPE
| Autor: | Yu-JenWang, 王昱仁 |
|---|---|
| Rok vydání: | 2010 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 98 The main purpose of this thesis is to investigate the dilute-nitride alloys and develop the InGaAsN materials lattice-matched to GaAs or Ge with near 1 eV bandgap for the use as a third-junction in the next generation of ultrahigh-efficiency four-junction solar cells. In the study of growing InGaAsN layers on GaAs substrates by MOVPE, high resolution X-ray diffraction and UV-VIS-NIR spectrophotometer were performed to characterize the epitaxial layers including the In, N composition and the material bandgap. To extend the absorption wavelength to 1 eV and reduce the lattice constant mismatch, the In and N content must be accurately controlled by TMIn/III ratio and DMHy/VT ratio. Using low temperature, moderate growth rate and high DMHy/VT ratio would enhance N incorporation. In addition, the use of TMGa instead of TEGa as gallium source revealed the better crystal quality and it could avoid the strong co-pyrolysis effect dramatically decreasing the growth rate. Then, the InGaAsN bulk layers were successfully grown on GaAs substrates within less than 800 ppm lattice mismatch under various growth temperature of 600°C, 575°C, 550°C and 525°C with the bandgap of 1.037 eV, 1.022 eV, 0.967 eV and 1.039 eV respectively. Especially, epitaxial temperature of 525°C was too low to be used for the device application due to the quite slow growth rate and relatively rough surface. Double heterojunction p-GaAs/i-InGaAsN/n-GaAs solar cells were also fabricated by introducing the InGaAsN intrinsic layer grown at different epitaxial temperatures to absorb the long wavelength region. In particular, the better optoelectronic properties of near 1 eV InGaAsN epilayer lattice-matched to GaAs could be obtained under the optimized growth temperature of 550°C, thus the short-circuit current density and conversion efficiency could reach 11.56 mA/cm2 and 1.79% respectively. Furthermore, we tried to optimize the device structure by increasing the absorption layer thickness to 1.5 μm and lowering the N content to 2.8% in the InGaAsN layer, the short-circuit current density could dramatically increase to 16.98 mA/cm2 and 15.59 mA/cm2 with the relative enhancement of 46.9% and 34.9% respectively, thus the energy conversion efficiency could be further improved to 2.69% and 2.47%. In the future, our long-term goal is to develop the InGaP/GaAs/1 eV/Ge tandem solar cells and apply the InGaAsN-based solar cells fabricated in this thesis as the third-junction to further improve the energy conversion efficiency. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
| Externí odkaz: |
|