To evaluate the performance of GaNAsBi alloys as solar cell materials, a GaNAsBi double-heterostructure pin solar cell was fabricated using plasma-assisted solid source molecular beam epitaxy. The addition of even a small amount of N (less than 1%) to the GaAsBi alloy significantly reduces the short-circuit current density (J sc ) of the solar cell. However, after thermal annealing, J sc increases by ∼6.5 times. After thermal annealing, the GaN 0.006 As 0.966 Bi 0.028 solar cells (bandgap (E g ) = 1.15 eV) exhibited an open-circuit voltage (V oc ) of 0.35 V, J sc of 10.2 mA cm −2 , and fill factor of 0.56. Based on the Urbach energy of Ga(N)AsBi, the decreased crystallinity associated with the addition of N leads to poor characteristics of GaNAsBi solar cells compared with those GaAsBi solar cells.

We investigated the effect of inserting a compositionally graded layer at the GaAsBi/GaAs interface on the photovoltaic and light-emission properties of GaAs/GaAsBi pin diodes. When the pin diode is operated as a solar cell, inserting a graded layer improves the open-circuit bandgap–voltage offset (W oc) to 0.51 V. This is comparable to or better than other materials—such as GaInNAs(Sb), which has a bandgap of 1.0 eV—that are expected to be used in multijunction solar cells. In contrast, W oc can be as large as 0.71 V for a pin diode without a graded layer. When it is operated as a light-emitting diode, inserting a graded layer in such a diode suppresses nonradiative recombination by a factor of 1/50 based on its electroluminescence intensity. Inserting a graded layer also makes it possible to avoid deterioration of the peculiar hetero-interface where the transition from the non-metallic nature of GaAs to the metallic nature of GaAsBi occurs. Moreover, the graded layer is effective in avoiding a pile-up of oxygen at the interface at low temperatures when growth is interrupted just before growing the GaAsBi layer. Thus, inserting a graded layer is the key to improving the performance of minority-carrier devices containing GaAsBi.

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Poster Sessions at the Fe/MgO(100) interface do not detect any oxygen diffusion in the Fe film showing a sharp interface with the Fe crystallographic cell tetragonally distorted to match the MgO crystal lattice. These results will be discussed in relation to the magnetic properties of the systems.

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