Highly packed InGaAs quantum dots on GaAs(311)B

Akahane, Kouichi; Kawamura, Takahiro; Okino, Kenji; Koyama, Hiromichi; Lan, Shen; Okada, Yoshitaka; Kawabe, Mitsuo; Tosa, Masahiro

doi:10.1063/1.122781

Cited by 77 publications

(37 citation statements)

References 6 publications

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“…Unfortunately, dot density of uniform QDs was not enough (about 1-3 Â 10 10 cm À2 ) because of the enhanced surface migration of indium species. In order to increase dot density, several growth techniques modifying the underlying layer structures have [5], on GaAs(3 1 1)B substrates [6] and on AlAs buffer layers [7]. In case of highly dense QDs, inhomogeneous broadening in the dot size was not narrow, and, in addition, coalescence of neighboring dots was more induced because of a small distance between the dots.…”

Section: Introductionmentioning

confidence: 99%

Self-assembled InAs quantum dots on GaSb/GaAs(0 0 1) layers by molecular beam epitaxy

Yamaguchi

Kanto

2005

Journal of Crystal Growth

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Section: Introductionmentioning

confidence: 99%

Self-assembled InAs quantum dots on GaSb/GaAs(0 0 1) layers by molecular beam epitaxy

Yamaguchi

Kanto

2005

Journal of Crystal Growth

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“…Modelling becomes necessary to gain a deeper insight of this issue. Substantially higher QD densities can be achieved by growing QDs on (311) substrates 21 instead of on (100) substrates, but this refinement has not yet been applied to cell manufacturing.…”

Section: Quantum Dot Ib Solar Cellsmentioning

confidence: 99%

“…For instance, using QD spacers with a thickness of 20 nm (as in most of the experimental work referenced here) instead of 80 nm (as in the tunnel-free cell 27,28 ), together with a larger QD surface density 21 (surface coverage of 50% instead of 10% in the cell analysed), would cause 25 the sub-bandgap current to increase to around 4.4 mA cnr 2 . However, the absorptance value that corresponds to this sub-bandgap current is not yet at the desirable value of unity.…”

Section: Summary and Challengesmentioning

confidence: 99%

Understanding intermediate-band solar cells

2012

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The intermediate-band solar cell is designed to provide a large photogenerated current while maintaining a high output voltage. To make this possible, these cells incorporate an energy band that is partially filled with electrons within the forbidden bandgap of a semiconductor. Photons with insufficient energy to pump electrons from the valence band to the conduction band can use this intermediate band as a stepping stone to generate an electron-hole pair. Nanostructured materials and certain alloys have been employed in the practical implementation of intermediate-band solar cells, although challenges still remain for realizing practical devices. Here we offer our present understanding of intermediate-band solar cells, as well as a review of the different approaches pursed for their practical implementation. We also discuss how best to resolve the remaining technical issues.T he intermediate-band (IB) solar cell consists of an IB material sandwiched between two ordinary n-and p-type semiconductors 1 , which act as selective contacts to the conduction band (CB) and valence band (VB), respectively (Fig. la). In an IB material, sub-bandgap energy photons are absorbed through transitions from the VB to the IB and from the IB to the CB, which together add up to the current of conventional photons absorbed through the VB-CB transition. In 1997 2 , researchers used hypotheses similar to those adopted by Shockley and Queisser in 1961 3 to derive a detailed balance-limiting efficiency of 63% for the IB solar cell, at isotropic sunlight illumination (concentration of 46,050 suns) and assuming Sun and Earth temperatures to be 6,000 K and 300 K, respectively (Fig. lb). This work also presented the Shockley-Queisser limiting efficiency of 41% for single-gap solar cells operating under the same conditions 2 . The limiting efficiency of the IB solar cell is similar to that of a triple-junction solar cell connected in series. However, the IB can be regarded 4 as a set of two cells connected in series (corresponding to the VB-IB and IB-CB transitions) and one in parallel (corresponding to the VB-CB transition). This provides the IB solar cell with additional tolerance to changes in the solar spectrum.An optimal IB solar cellhas a total bandgap of about 1.95 eV, which is split by the IB into two sub-bandgaps of approximately 0.71 eV and 1.24 eV The quasi-Fermi levels (QFLs) or electrochemical potentials of the electrons in the different bands are usually close to the edges of the bands. Because the voltage of any solar cell is the difference between the CB QFL at the electrode in contact with the n-type side and the VB QFL at the electrode in contact with the p-type side, the maximum photovoltage of the IB solar cell is limited to 1.95 eV, although it is still capable of absorbing photons of energy above 0.71 eV In contrast, single-gap solar cells cannot supply a voltage greater than the lowest photon energy they can absorb. IB solar cells can deliver a high photovoltage by absorbing two subbandgap photons to produce one high ...

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“…However, these self-assembled QDs provide weak sub-bandgap absorption and, subsequently low additional I L . Several strategies have been proposed to counteract this lack of absorption, such as reducing the size of the dots [10], using high-index substrates to order and pack the in-plane dots [11] or employing metal nanoparticles [12] or diffraction grid patterns [13] as light trapping techniques. However, these techniques are still challenging to implement.…”

Section: Inas/gaasn Quantum Dot (Qd) Strain Balance Solar Cellsmentioning

confidence: 99%

Voltage limitation analysis in strain-balanced InAs/GaAsN quantum dot solar cells applied to the intermediate band concept

Linares

López

Ramiro

et al. 2015

Solar Energy Materials and Solar Cells

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IBSCs. In these cells, the dilute nitrogen in the barrier plays an important role for the strain-balance (SB) of the QD layer region that would otherwise create dislocations under the effect of the accumulated strain. The introduction of GaAsN SB layers allows increasing the light absorption in the QD region by multi-stacking more than 100 QD layers. The photo-generated current density (J L ) versus V OC was measured under varied concentrated light intensity and temperature. We found that the V OC of the cell at 20K is limited by the bandgap of the GaAsN barriers, which has important consequences regarding IBSC bandgap engineering that are also discussed in this work.

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Highly packed InGaAs quantum dots on GaAs(311)B

Cited by 77 publications

References 6 publications

Self-assembled InAs quantum dots on GaSb/GaAs(0 0 1) layers by molecular beam epitaxy

Self-assembled InAs quantum dots on GaSb/GaAs(0 0 1) layers by molecular beam epitaxy

Understanding intermediate-band solar cells

Voltage limitation analysis in strain-balanced InAs/GaAsN quantum dot solar cells applied to the intermediate band concept

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