An extended defect as a sensor for free carrier diffusion in a semiconductor

Gfroerer, T. H.; Zhang, Yong; Wanlass, M. W.

doi:10.1063/1.4775369

Cited by 37 publications

(62 citation statements)

References 17 publications

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“…It is important to make such comparisons under the same laser power because it has been shown in previous work that the diffusion length is sensitive to the excitation power [6,8,9]. Clearly, the three profiles are quite close to each other, which indicates that the diffusion lengths for electrons of different kinetic energies are approximately the same.…”

Section: Resultsmentioning

confidence: 99%

“…The semiconductor sample used was a 1 μm thick high-quality GaAs (gallium arsenide) thin-film sandwiched between two GaInP (gallium indium phosphide) layers with a higher bandgap [6,8,9]. GaAs was chosen because of the availability of the high-quality sample as well as its important role in many technology applications, including high efficiency solar cells, semiconductor lasers, and high-speed electronics.…”

Section: Methodsmentioning

confidence: 99%

“…Because electrons with different kinetic energies emit photons at different wavelengths, the spatial variation of the PL signal for different wavelengths had to be measured and compared to test the hypothesis. In previous studies, both electron and laser beams have been used to generate a local electron population, but the spatial profiles of light emission were typically measured either by including the whole emission spectrum (non-wavelength selective) [5] or by selecting a single narrow band near the bandgap [6,8,9,10]. Thus, the potential wavelength dependence had not been explicitly examined.…”

Section: Introductionmentioning

confidence: 99%

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Optical Imaging of Diffusive Electrons with Different Kinetic Energies in a Semiconductor

Zhang

2018

Chronicle of The New Researcher

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Author's Summary: When electrons in a semiconductor are generated by light, they can diffuse for a certain distance before being recombined. The length of diffusion is indicative of the material quality but, unfortunately, the motions of the electrons are difficult to observe directly. The focus of this project was to find a simple and effective way to measure the diffusion length of electrons in a semiconductor material. A laser was used to generate electrons in a small area and an imaging camera was used to map their distribution through the light they emitted as they diffused. This technique can be implemented to quickly and accurately assess the quality of any semiconductor material. AbstractIn this project, a photoluminescence (PL) imaging technique was developed for probing electron diffusion in a semiconductor thin film. This technique was applied to investigate electron diffusion in GaAs for electrons of different kinetic energies. A tightly focused laser beam at 532 nm was used to generate electrons in an area of about 0.72 μm, and the spatial profile of the PL in an area much larger than that of the laser excitation site was imaged by a digital camera. Analysis of the PL images at different wavelengths indicated that the electrons maintain the same thermal distribution during diffusion and exhibit a common diffusion length of approximately 3.5 ± 0.2 μm.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Optical Imaging of Diffusive Electrons with Different Kinetic Energies in a Semiconductor

Zhang

2018

Chronicle of The New Researcher

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“…Extended defects, such as dislocations and grain boundaries, are more difficult to properly evaluate. Photoluminescence and cathodoluminescence (CL) mapping techniques are routinely used to spatially resolve regions of higher nonradiative recombination associated with these defects [7][8][9]. Temporally resolved PL or absorption mapping techniques have also been used on occasion to determine the localized effects of grain boundaries [10] and stacking faults [11] on carrier lifetimes.…”

Section: Introductionmentioning

confidence: 99%

Carrier Decay and Diffusion Dynamics in Single-Crystalline CdTe as Seen via Microphotoluminescence

et al. 2014

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The ability to spatially resolve the degree to which extended defects impact carrier diffusion lengths and lifetimes is important for determining upper limits for defect densities in semiconductor devices. We show that a new spatially and temporally resolved photoluminescence (PL) imaging technique can be used to accurately extract carrier lifetime values in the immediate vicinity of dark-line defects in CdTe=MgCdTe double heterostructures. A series of PL images captured during the decay process show that extended defects with a density of 1.4 × 10 5 cm −2 deplete photogenerated charge carriers from the surrounding semiconductor material on a nanosecond time scale. The technique makes it possible to elucidate the interplay between nonradiative carrier recombination and carrier diffusion and reveals that they both combine to degrade the PL intensity over a fractional area that is much larger than the physical size of the defects. Carrier lifetimes are correctly determined from numerical simulations of the decay behavior by taking these two effects into account. Our study demonstrates that it is crucial to measure and account for the influence of local defects in the measurement of carrier lifetime and diffusion, which are key transport parameters for the design and modeling of advanced solar-cell and light-emitting devices.

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“…Thus, the distance a carrier can move in real space during its lifetime is increased, and the nonradiative recombination at extended defects starts to dominate. 14,18 Moreover, at high carrier densities, the carrier mobility is additionally enhanced due to carrier degeneracy. 19 The carrier-density-enhanced recombination at the extended defects with distances between them larger than the average distance the carrier can travel during its lifetime at low temperature but comparable at room temperature is consistent with the supposed recombination at growth domains observed in AlGaN epilayers by scanning near-field optical microscopy.…”

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confidence: 99%

Temperature-dependent efficiency droop in AlGaN epitaxial layers and quantum wells

et al. 2016

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Luminescence efficiency droop has been studied in AlGaN epitaxial layers and multiple quantum wells (MQWs) with different strength of carrier localization in a wide range of temperatures. It is shown that the dominant mechanism leading to droop, i.e., the efficiency reduction at high carrier densities, is determined by the carrier thermalization conditions and the ratio between carrier thermal energy and localization depth. The droop mechanisms, such as the occupation-enhanced redistribution of nonthermalized carriers, the enhancement of nonradiative recombination due to carrier delocalization, and excitation-enhanced carrier transport to extended defects or stimulated emission, are discussed.

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An extended defect as a sensor for free carrier diffusion in a semiconductor

Cited by 37 publications

References 17 publications

Optical Imaging of Diffusive Electrons with Different Kinetic Energies in a Semiconductor

Optical Imaging of Diffusive Electrons with Different Kinetic Energies in a Semiconductor

Carrier Decay and Diffusion Dynamics in Single-Crystalline CdTe as Seen via Microphotoluminescence

Temperature-dependent efficiency droop in AlGaN epitaxial layers and quantum wells

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