MOVPE SiGeSn development for the next generation four junction solar cells

Abstract

The Multijunction (MJ) monolithic approach is very attractive for a competitive concentrating photovoltaic (CPV) technology; it has been successfully applied for InGaP/GaInAs/Ge triple-junction structures but it is more difficult to be exploited for manufacturing 4-junction solar cells, in particular when III-V and IV elements are both used. So far, the integration of the 1 eV SiGeSn material in the lattice-matched InGaP/GaInAs/Ge triple-junction structure has required the utilization of two different growth apparatus, nearly losing the economic advantage of the monolithic architecture, owing to the related higher capital expenditure. The central technical challenge for realizing InGaP/GaInAs/SiGeSn/Ge solar cell at low cost, with an industrial approach, lies in the growth of III-V and IV elements in the same MOVPE equipment, by solving the "cross contamination" problem among the III-V elements and the IV elements. In this contribution, for the first time, the results of the investigation concerning the growth of SiGe(Sn) and III-V compounds in the same MOVPE growth chamber are presented. The epitaxial layers have been characterized by XRD, SEM, TEM, EDX, SIMS and ECV profiling. It is eventually shown that by starting from a modification of the MOVPE equipment and by setting up proper growth condition the contamination of III-V elements in IV based materials can be drastically reduced from 10 20 cm-3 to 2*10 17 cm-3 , while the contamination of IV elements in III-V compounds can be reduced from 4-5*10 17 cm-3 to 6*10 16-3*10 14 cm-3 depending on the substrate used.

Comparison of first principles and semi-empirical models of the structural and electronic properties of $$\hbox {Ge}_{1-x}\hbox {Sn}_{x}$$ alloys

“…In addition to applications in CMOS-compatible light-emitting devices, research interest in (Si)Ge 1−x Sn x alloys has also been driven by potential applications in tunneling fieldeffect transistors [12][13][14] and multi-junction solar cells. [15][16][17] Comparison by Moontragoon et al 18 between empirical pseudopotential calculations for Ge 1−x Sn x carried out using the virtual crystal approximation (VCA), and a direct atomistic (alloy supercell) approach, highlighted significant differences in key properties including band gap bowing. This suggested the potential importance of band mixing and alloy disorder effects in Ge 1−x Sn x alloys.…”

Impact of defects on photoexcited carrier relaxation dynamics in GeSn thin films

“…Germanium tin (GeSn) group-IV semiconductors are promising absorber/emission materials for the novel infrared (IR) optoelectronic devices such as photo-detectors [1,2], lightemitting diodes [3], continuous-wave and pulsed lasers [4,5], and solar cells [6,7], which are fully compatible with the complementary metal-oxide-semiconductor process. The main advantage of these materials is the possibility to obtain a higher absorptivity and quantum yield of luminescence in comparison with indirect-bandgap crystalline silicon, * Author to whom any correspondence should be addressed.…”

A new theoretical approach for the performance simulation of multijunction solar cells

“…For the Ge bottom cell, the cell parameters are different for the 2T and for the 3T QJ, as the polarity of the junctions is inverted and different doping levels are selected. For SiGeSn, experimental data on the absorption coefficient measured on MOVPE grown samples have been used, imposing a threshold absorption at 1eV . Series resistance effect and a grid shadowing of 4% have been also included.…”

“…The combination of group IV and III to V elements have paved the way for developing frontier lattice matched MJ solar cells, in, particular, the InGaP/InGaAs/SiGeSn/Ge QJ ones, in which the SiGeSn plays the role of the third junction, with a 1eV energy gap ( E g ) . However, the realization of a 2T QJ structure, by combining IV and III to V elements in the same metal organic chemical vapour deposition (MOVPE) growth chamber is challenging, because of the cross contamination problem . A 2T InGaP/InGaAs/SiGeSn/Ge solar cell structure is, for example, reported in Figure , in which we notice the presence of an (In)GaAs bottom TD (BTD).…”