Quantum Wells, Wires and Dots

Harrison, P.

doi:10.1002/0470010827

Cited by 716 publications

(643 citation statements)

References 21 publications

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“…This ideal value could be approached through the use of gratings to diffract the photons and make them propagate in directions laterally along the solar cell. In the case of smaller QDs in immiscible materials, the interband matrix elements discussed above may increase due to the appearance of further terms that are negligible in the large QDs used so far 51 .…”

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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Section: Summary and Challengesmentioning

confidence: 99%

Understanding intermediate-band solar cells

2012

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“…After calculating the electronic states of the QCL, the wavefunctions were then used to evaluate all the principal electron-electron and electron-LO phonon intra-and interperiod scattering rates [15]. The resulting rate equations must be solved self-consistently since the subband populations depend upon both the initial and final populations, and hence the process was repeated until the subband populations converged.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

Thermal effects in InGaAs/AlAsSb quantum-cascade lasers

Evans

Jovanović

Indjin

et al. 2006

IEE Proceedings - Optoelectronics

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A quantum cascade laser (QCL) thermal model is presented. Based upon a finite-difference approach, the model is used in conjunction with a self-consistent carrier transport model to calculate the temperature distribution in a near-infrared InGaAs/AlAsSb QCL. The presented model is used to investigate the effects of driving conditions and device geometries on the active region temperature, which has a major influence on the device performance. A buried heterostructure (BH) combined with epilayer-down bonding is found to offer the best performance compared to alternative structures and has thermal times constants up to eight times smaller. The presented model provides a valuable tool for understanding the thermal dynamics inside a QCL and will help to improve operating temperatures.

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“…1 In particular, GaAs/InAs core/shell NWs are of interest for a wide range of applications, 2 since the lower band gap semiconductor InAs with a band gap of E g,InAs ¼ 0.35 eV 3 is grown onto a higher band gap semiconductor GaAs with E g,GaAs ¼ 1.42 eV 3 forming a type I heterostructure. 1 Due to the band offset at the interface, a certain number of electrons and holes will diffuse from the wide-gap to the narrow-gap side of the heterostructure, providing an accumulation of electrons in the InAs shell close to the interface. 4 Moreover, the large lattice mismatch between the core and shell material originates misfit strain which will also modify the band structure at both sides of the interface.…”

Section: Introductionmentioning

confidence: 99%

Band bending at the heterointerface of GaAs/InAs core/shell nanowires monitored by synchrotron X-ray photoelectron spectroscopy

Khanbabaee

Bussone

Knutsson

et al. 2016

Journal of Applied Physics

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Unique electronic properties of semiconductor heterostructured nanowires make them useful for future nano-electronic devices. Here, we present a study of the band bending effect at the heterointerface of GaAs/InAs core/shell nanowires by means of synchrotron based X-ray photoelectron spectroscopy. Different Ga, In, and As core-levels of the nanowire constituents have been monitored prior to and after cleaning from native oxides. The cleaning process mainly affected the Asoxides and was accompanied by an energy shift of the core-level spectra towards lower binding energy, suggesting that the As-oxides turn the nanowire surfaces to n-type. After cleaning, both As and Ga core-levels revealed an energy shift of about À0.3 eV for core/shell compared to core reference nanowires. With respect to depth dependence and in agreement with calculated strain distribution and electron quantum confinement, the observed energy shift is interpreted by band bending of core-levels at the heterointerface between the GaAs nanowire core and the InAs shell. Published by AIP Publishing. [http://dx

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Quantum Wells, Wires and Dots

Cited by 716 publications

References 21 publications

Understanding intermediate-band solar cells

Understanding intermediate-band solar cells

Thermal effects in InGaAs/AlAsSb quantum-cascade lasers

Band bending at the heterointerface of GaAs/InAs core/shell nanowires monitored by synchrotron X-ray photoelectron spectroscopy

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