Studies on effects of pulse-light irradiation on InGaAsN crystal growth for super high efficiency solar cells

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III-V compound multi-junction (MJ) tandem solar cells have attracted a considerable attention in space and terrestrial applications due to the great potential for obtaining high conversion efficiency. The group-III arsenide nitride compound InGaAsN thin film is one of the candidates for the future solar cells, because it has a lattice constant matched with that of substrate Ge and has 1.0 eV band gap. To realize the good InGaAsN film, we have been developing chemical beam epitaxy (CBE) technique. In this work, to improve the electrical properties of the grown film, that is, to control the N concentration and to reduce the impurity concentration, we studied the effects of light irradiation during the growth on the film properties. First, we developed the new CBE system, where the pulse light can irradiate the growing surface at the same period of the source gas supply. The N concentration in the grown film was increased and the C concentration was decreased by the light irradiation to the growing surface. These results suggested the possibilities of the control of surface reactions by the light irradiation.