| AVS 62nd International Symposium & Exhibition | |
| Electronic Materials and Processing | Thursday Sessions |
| Session EM+EN-ThA |
| Session: | Materials for Light Management |
| Presenter: | Tsubasa Nakamura, University of Miyazaki, Japan |
| Authors: | T. Nakamura, University of Miyazaki, Japan K. Matsuochi, University of Miyazaki, Japan T. Murakami, University of Miyazaki, Japan H. Suzuki, University of Miyazaki, Japan K. Toprasertpong, The University of Tokyo, Japan M. Sugiyama, The University of Tokyo, Japan Y. Nakano, The University of Tokyo, Japan T. Ikari, University of Miyazaki, Japan A. Fukuyama, University of Miyazaki, Japan |
| Correspondent: | Click to Email |
Insertion of a multiple quantum-well (MQW) structure into the absorbing layer of solar cells is promising for accomplishing higher conversion efficiency. Recently, a MQW with a very thin barrier structure has been proposed to enhance the conversion efficiency [1]. The coupling of the wave functions between adjacent quantum wells causes a mini-Brillouin zone along the growth direction, which results in the formation of miniband. We have discussed carrier escaping mechanism in MQW by using photoreflectance (PR) and photothermal spectroscopy (PPT) and found that internal electric field in the QW region might affect the recombination probability [2]. In this study, we investigate the effect of internal electric filed on the miniband width.
Three kinds of MQW samples were grown by a metal-organic vapor phase epitaxy technique. Two GaAs p-i-n solar cell structure samples with MQWs in the i-layer were prepared. The doping levels in the p- and n-type layer were changed and this induced the different strength of the electric field in the absorbing layer. Another sample had GaAs n-n structures without any electric field in the absorbing layer. The thicknesses of the well barrier were changed from 2 to 6 nm for discussing the detailed miniband formation. PR and PPT measurements were carried out at room temperature. The miniband width was estimated from the difference of the peak energies of the PR modulus spectra. The lower and higher energy peak correspond to the energies of bottom and top of the miniband, respectively. The PPT method is used to detect the heat generated by non-radiative recombination of photo generated carriers. The miniband width was also calculated from the Gaussian decomposition technique of the observed PPT spectra [3].
Decrease of the miniband width by increasing the barrier width was observed for all samples. This is coincide with the theoretical prediction. The miniband width for n-n structure is considered to be larger than that of p-i-n structure. Applied electric filled may reduce the wave function overlapping between the adjacent wells. The increase of the miniband width by the electric field for the p-i-n structure sample was observed. However, the increase of the miniband widths for n-n structure could not be confirmed from the PR spectra. Since the PPT measurement is more sensitive for estimating the band edge transition, effect of the electric field may be more clearly observed by comparing the PR and PL spectra.[1] Y. Wang, et al., J. Cryst. Growth 352, 194 (2012).
[2] T. Aihara et al., J. Appl. Phys. 116, 044509 (2014).
[3] T. Aihara et al., J. Appl. Phys. 117, 084307 (2015).