Photoluminescence and sub band gap absorption of CuGaSe2 thin films

Meeder, A.; Marrón, D. Fuertes; Chu, V.; Conde, J.P.; Jäger-Waldau, Arnulf; Rumberg, A.; Lux‐Steiner, Martha Ch.

doi:10.1016/s0040-6090(01)01545-0

Cited by 29 publications

(36 citation statements)

References 9 publications

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“…Photoluminescence (PL) studies on CuGaSe 2 found donor-acceptor-pair (DAP) transitions between 1.0 and 1.3 eV. 12,13 But estimations of the defect levels in these studies are based on calculations rather than measuring the activation energy directly. In Ref.…”

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confidence: 99%

“…12, the distance of next-nearest donor-acceptor pairs for different lattice positions was used, whereas in Ref. 13, the deep levels were calculated from the energetic position of bound excitons. In this paper, we will present further insights into the possible recombination centers in CuGaSe 2 and their influence on the intensity dependence of the PL measurement.…”

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confidence: 99%

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Revisiting radiative deep-level transitions in CuGaSe2 by photoluminescence

Spindler

Regesch

Siebentritt

2016

Applied Physics Letters

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Recent defect calculations suggest that the open circuit voltage of CuGaSe2 solar cells can be limited by deep intrinsic electron traps by GaCu antisites and their complexes with Cu-vacancies. To gain experimental evidence, two radiative defect transitions at 1.10 eV and 1.24 eV are characterized by steady-state photoluminescence on epitaxial-grown CuGaSe2 thin films. Cu-rich samples are studied, since they show highest crystal quality, exciton luminescence, and no potential fluctuations. Variations of the laser intensity and temperature dependent measurements suggest that emission occurs from two deep donor-like levels into the same shallow acceptor. At 10 K, power-law exponents of 1 (low excitation regime) and 1/2 (high excitation regime) are observed identically for both transitions. The theory and a fitting function for the double power law is derived. It is concluded that the acceptor becomes saturated by excess carriers which changes the exponent of all transitions. Activation energies determined from the temperature quenching depend on the excitation level and show unexpected values of 600 meV and higher. The thermal activation of non-radiative processes can explain the distortion of the ionization energies. Both the deep levels play a major role as radiative and non-radiative recombination centers for electrons and can be detrimental for photovoltaic applications.

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Revisiting radiative deep-level transitions in CuGaSe2 by photoluminescence

Spindler

Regesch

Siebentritt

2016

Applied Physics Letters

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“…PL has some advantages over CL. For example a laser of lower energy than the width of the band gap can be chosen to probe for defects, donors or acceptors inside the band gap 62 .…”

Section: Photoluminescence and Time-resolved Photoluminescencementioning

confidence: 99%

Optical and Structural Characterization of GaN Based Hybrid Structures and Nanorods

Forsberg

2015

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GaN belongs to the group III nitrides and is today the material of choice for efficient blue light emission, enabling solid state white lighting by combining red, blue and green light emitting diodes (LED) or by having a blue LED illuminating a phosphor. By combining GaN quantum well (QW) structures with colloids, nanoparticles or polyfluorene films, LEDs may be fabricate at lower cost. Such hybrid structures are promising for future micro-light sources in full-color displays, sensors and imaging systems. In this work, hybrid structures based on an MOCVD grown GaN QW sandwiched between two layers of AlGaN have been studied. On top of the structure, colloidal ZnO nano-crystals were deposited by spin-coating. Time-resolved photoluminescence was used to investigate the QW exciton dynamics in these hybrids depending on the cap layer thickness. From comparison of the recombination rate in the bare QW structure and the hybrid, the efficiency of the non-radiative resonant energy transfer between the QW and the nano-crystals could be obtained.Bulk GaN of large area is difficult to synthesize. Thus, due to lack of native substrates, GaN-based structures are grown on SiC or sapphire, which results in high threading dislocation density in the active layer of the device. Fabricating GaN nanorods (NR) can be a way to produce GaN with lower defect density since threading dislocations are annihilated toward the NR wall during growth. Here, GaN(0001) NRs grown on Si(111) substrates by magnetron sputter epitaxy using a liquid Ga target have been investigated. Sputter deposition has the advantage of being easy to scale up for depositions on large surfaces. It is also possible to deposit at lower temperatures, which allows the use of substrates with lower decomposition temperature. In the second paper of this thesis, optical and structural properties of sputtered GaN NRs have been studied.

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“…Thus, excitation of 100% spinpolarized carriers occurs only within a small energy window near the band gap energy. With decreasing Cu content the material band edge becomes less well defined 5 and this also leads to an increased intermixing of the lh and hh states.…”

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Optical spin injection in CuGaSe2∕GaAs films

Itskos

Murray

Meeder³

et al. 2006

Applied Physics Letters

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We have investigated polarization-resolved photoluminescence in epitaxially grown CuGaSe 2 / GaAs͑001͒ films. Spin-polarized excitons are optically excited both below and above the characteristic crystal field splitting of the chalcopyrite. At low temperatures, a large exciton spin polarization of 35% is measured under resonant pumping but this is reduced by an order of magnitude and reverses its sign for nonresonant excitation. The measurements suggest that optical pumping within a small energy window just above the band gap results in the preferential generation of light holes and electrons that exhibit a long spin relaxation time, comparable to the recombination time in CuGaSe 2 . © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2233684͔There is considerable interest in the spin degree of freedom of carriers in the emerging field of spintronics but the realization of practical spintronic devices depends on efficient injection, transport, and detection of spin-polarized carriers. Thus, it is of interest to study materials where a high spin polarization can be realized. CuGaSe 2 , a member of the chalcopyrite family, is a promising candidate. It is a direct band gap semiconductor ͑band gap energy E g = 1.731 eV at T =10 K͒ with applications in optoelectronics technology, for example, red-light-emitting diodes, light detectors, and solar cell devices. In this letter we report on polarization-resolved photoluminescence experiments on GuGaSe 2 films grown on GaAs substrates to evaluate the potential of this material for spintronic applications.In optical pumping experiments on bulk zinc-blende materials ͓Fig. 1͑a͔͒, the radiative selection rules allow a population of spin-polarized electrons and holes to be excited by circularly polarized light. Due to the degeneracy of the heavy hole ͑hh͒ and light hole ͑lh͒ bands at the center of the Brillouin zone and the 3:1 relative strength of the hh/lh transitions, the maximum optical polarization that can be emitted, P circ , is limited to 25%, corresponding to a maximum spin injected polarization P spin of 50%.1 In strained GaAs films, an internal crystal field is generated that lifts the degeneracy of the valence band so that in principle a 100% spin-polarized electron population can be photogenerated. Strain can be induced by growing on lattice mismatched substrates but this reduces the crystal quality and limits the achievable film thickness. Thick films usually exhibit a high dislocation density and poor optical properties.By contrast most chalcopyrites ͑I-III-VI 2 -compounds͒ and pnictides 2 have an internal crystal field splitting ⌬cf, which results in an energy splitting of the lh and hh bands at the center of the Brillouin zone. Lifting of the valence band degeneracy allows, in principle, the optical injection of 100% spin-polarized carriers, corresponding to emission of 100% circular polarized light 1 ͑P spin = P circ ͒. Figure 1͑b͒ shows the schematic band structure of one widely investigated member of the chalcopyrite family, CuGaSe 2 . This material exhib...

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Photoluminescence and sub band gap absorption of CuGaSe2 thin films

Cited by 29 publications

References 9 publications

Revisiting radiative deep-level transitions in CuGaSe2 by photoluminescence

Revisiting radiative deep-level transitions in CuGaSe2 by photoluminescence

Optical and Structural Characterization of GaN Based Hybrid Structures and Nanorods

Optical spin injection in CuGaSe2∕GaAs films

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