The intermediate-band solar cell is designed to provide a large photogenerated current while maintaining a high output voltage. Nanostructured materials and certain alloys have been employed in the practical implementation of these devices. This Progress Article reviews the range of different approaches and discusses how to resolve the remaining technical issues.

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Understanding intermediate-band solar cells

Self-organization of nanostructures in semiconductor heteroepitaxy

Extensive literature and publications on intermediate band solar cells (IBSCs) are reviewed. A detailed discussion is given on the thermodynamics of solar energy conversion in IBSCs, the device physics, and the carrier dynamics processes with a particular emphasis on the two-step inter-subband absorption/recombination processes that are of paramount importance in a successful implementation high-efficiency IBSC. The experimental solar cell performance is further discussed, which has been recently demonstrated by using highly mismatched alloys and high-density quantum dot arrays and superlattice. IBSCs having widely different structures, materials, and spectral responses are also covered, as is the optimization of device parameters to achieve maximum performance.

/pdf/intermediate-band-solar-cells-recent-progress-and-future-3jnb8vcjy1.pdf

Intermediate band solar cells: Recent progress and future directions

Fabrication of ultra-high density InAs-stacked quantum dots by strain-controlled growth on InP(3 1 1)B substrate

Semiconductor quantum-dot nanostructures are interesting objects for fundamental as well as practical reasons. Fundamentally, they can form the basis of systems in which to study the quantum mechanics of electrons confined in zero-dimensional (0-D) space. In practice, the dots can be embedded in the active regions of a new class of electronic and optoelectronic devices with novel functionalities. This paper reviews the state-of-the-art in the use of these objects in infrared detectors. It describes the progress, challenges, and projections for continued development of normal-incidence intersublevel detectors operating in the spectral region between 6 and 20 /spl mu/m.

Semiconductor quantum-dot nanostructures: Their application in a new class of infrared photodetectors

We have fabricated highly packed and ordered In0.4Ga0.6As quantum dots (QDs) array on GaAs(311)B substrate without coalescence of QDs. Reflection high-energy electron diffraction and Auger spectra suggest the inhomogeneous distribution of In and Ga in QD. In concentration near the surface of QD is larger than that of the inside, and the inhomogeneous distribution of In and Ga in QDs prevents QDs from merging.

Highly packed InGaAs quantum dots on GaAs(311)B

Ordered In0.4Ga0.6As quantum dots (QDs), with the density of 109 cm-2–1011 cm-2, are fabricated on GaAs(311)B substrates by atomic-hydrogen assisted molecular beam epitaxy. The density and the dot size are mainly changed by the growth temperature between 460°C and 520°C. In sharp contrast to InAs, where we can hardly observe any ordering, and coalescence or merging of dots occurs beyond a thickness of 4 monolayers, the high-density In0.4Ga0.6As QDs do not coalesce even when the QDs are in contact with each other. The inhomogeneuos distribution of In and Ga in the QDs which are In rich at the surface is found to be responsible for this unusual behavior by reflection high energy electron diffraction studies. The atomic force microscope images show that a surface coverage of nearly 100% can be achieved. It implies the existence of lateral coupling between QDs, which is strongly supported by the photoluminscence measurements.

https://iopscience.iop.org/article/10.1143/JJAP.38.491/pdf

Hiromichi Koyama

Papers

Highly packed InGaAs quantum dots on GaAs(311)B

Self-Organization of High-Density III?V Quantum Dots on High-Index Substrates