Molecular beam epitaxial growth of intermediate-band materials based on GaAs:N δ-doped superlattices

Abstract

We fabricated GaAs:N δ-doped superlattices (SLs) by molecular beam epitaxy and investigated their potential as an intermediate-band photoabsorber in high-efficiency solar cells. The N area concentration in a N δ-doped layer was well controlled by adjusting the fabrication conditions, and the SLs with the average N composition of up to 1.5% were obtained. The SL minibands related to the N-induced E + and E % conduction subbands were formed with well-separated bottom energies of up to 0.4 eV, indicating the suitability of this material system for use in intermediate-band solar cells. A two-step photoabsorption process in a solar cell with the SL absorber was successfully demonstrated through external quantum efficiency measurements under additional infrared illumination at room temperature.

Growth and evaluation of GaAsN films with different N distribution grown by atomic layer epitaxy method

“…Here, we would like to make small conclusion for growth. Although superlattice periods were slightly fluctuated, we have successfully grown GaAsN thin films with different N distribution In addition, we would like to note that the films grown in this study were different from the δ-doped ones discussed in the literature [20][21][22][23] in points of small interdiffusion of N atoms and shorter period of superlattice. Thus, the effects of N distribution, in other words the effects of spacing of adjacent N atoms in GaAsN layers, on electrical properties could be evaluated using these films instead of superlattice structures with long period.…”

“…During MBE growth of GaAs films, radical N was supplied on GaAs surfaces to make δdoping layer, and δ-doped superlattices of N atoms between GaAs layers were fabricated. [20][21][22][23] Due to high energy of RF plasma, N atoms incorporated into the GaAs matrix not only on the surface but also several inside layers. In other words, N atoms distributed several layers.…”

“…Thus, above studies focused on electrical properties of superlattice structures with long periods (∼a few nm) 20,21,23) or luminesce property from single δ-doping layer. 22) To reveal effects of N distribution on electrical properties, it is necessary to control N distribution in order of few atomic layers.…”

Effects of carrier-blocking barrier height on two-step photocurrent generation in dilute nitride intermediate band solar cells

“…[13][14][15][16][17][18] So far, prototype IBSCs based on GaAsN and GaAsPN alloys which use the energetically lower E − band as the IB while the upper E + band as the CB have been reported. [19][20][21][22][23][24] In terms of electrical isolation of the IB from the contact layers, the importance of a carrier-blocking layer placed at the edge of dilute nitride IB absorbers was pointed out. Lopez et al showed enhanced optical transitions relating to the CB-IB gap in GaAsN with a carrier-blocking structure.…”