Abstract
Gallium phosphide (GaP) is an ideal candidate to implement a III-V nucleation layer on a silicon substrate. The optimization of this nucleation has been pursued for decades, since it can form a virtual substrate to grow monolithically III-V devices. In this work we present a GaP nucleation approach using a standard MOVPE reactor with regular precursors. This design simplifies the epitaxial growth in comparison to other routines reported, making the manufacturing process converge to an industrial scale. In short, our approach intends to mimic what is done to grow multijunction solar cells on Ge by MOVPE, namely, to develop a growth process that uses a single reactor to manufacture the complete III-V structure, at common MOVPE process temperatures, using conventional precursors. Here, we present the different steps in such GaP nucleation routine, which include the substrate preparation, the nucleation itself and the creation of a p-n junction for a Si bottom cell. The morphological and structural measurements have been made with AFM, SEM, TEM and Raman spectroscopy. These results show a promising surface for subsequent III-V growth with limited roughness and high crystallographic quality. For its part, the electrical characterization reveals that the routine has also formed a p-n junction that can serve as bottom subcell for the multijunction solar cell.
Highlights
IntroductionBut they are too expensive for terrestrial applications due to the raw materials involved and production costs
In this study we present a simpler routine for the growth of Gallium phosphide (GaP) layers on Si, that could be implemented in any standard MOVPE reactor, used to grow III-As and III-P
–both nucleation and device layers– and in a single MOVPE reactor. This process mimics what is done for GaInP/Ga(In)As/Ge triple-junction solar cells grown on a Ge wafer, where the nucleation and active layers are grown in a single run, using standard precursors, while creating the Ge bottom cell in the wafer during the first steps of the growth. With this target in mind, in this work we present such a GaP on Si MOVPE nucleation routine, which consists of: (1) a thermal annealing step for deoxidation and contaminant removal; (2) an AsH3 pre-exposure, which serves as a cleaning aide and to improve the superficial wetting; and (3) the growth of the GaP layer proper
Summary
But they are too expensive for terrestrial applications due to the raw materials involved and production costs. In view of this situation, in the search for photovoltaic progress, alternative new generations of solar cells have awakened great interest. Such is the case of the conjugation of III-V multijunction solar cells on silicon substrates. These architectures can combine the high efficiency of multijunction solar cells with the low-cost advantages of large area silicon substrates [5,6,7]. This integration is not direct and must tackle key difficulties, such as the large difference in thermal expansion coefficients and their significant lattice mismatch
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