Forbidden Band‐Edge Excitons of Wurtzite‐GaP: A Theoretical View

Belabbes, Abderrezak; Bechstedt, F.

doi:10.1002/pssb.201800238

Cited by 17 publications

(22 citation statements)

References 39 publications

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“…This difference could explain the unexpected PL transitions. Previous experimental and theoretical investigations suggest that the GaP WZ structure is a pseudo-direct band gap material with a lower band gap of 2.13 eV (at 4 K) as compared to 2.34 eV (at 10 K) for the GaP ZB structure [35] [36].…”

Section: Resultsmentioning

confidence: 93%

Stacking defects in GaP nanowires: Electronic structure and optical properties

Gupta

Goktas

Rao

et al. 2019

Journal of Applied Physics

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Formation of twin boundaries during the growth of semiconductor nanowires is very common. However, the effects of such planar defects on the electronic and optical properties of nanowires are not very well understood. Here, we use a combination of ab initio simulation and experimental techniques to study these effects. Twin boundaries in GaP are shown to act as an atomically-narrow plane of wurtzite phase with a type-I homostructure band alignment. Twin boundaries and stacking faults (wider regions of the wurtzite phase) lead to the introduction of shallow trap states observed in photoluminescence studies. These effects should have a profound impact on the efficiency of nanowire-based devices. * rubelo@mcmaster.ca 1 arXiv:1810.01194v2 [cond-mat.mtrl-sci] 11 Mar 2019 III-V semiconductor nanowires (NWs) have applications in electronic, optoelectronic, and photonic devices [1]. III-V NWs can be grown epitaxially on Si making integration of III-V optoelectronic devices with Si-based technology possible [2][3][4]. NWs with embedded quantum dots (e.g.GaAs quantum dots in GaP NWs) have shown potential for use in light-emitting diodes (LEDs), lasers and photodetectors [5].Crystal imperfections in 111 oriented III-V NWs is one of the factors that can limit the performance of optoelectronic devices. Twin boundaries (TBs) are one of the most abundant planar defects observed in NWs [6] as well as bulk semiconductors [7]. A very high twin plane density is usually observed in NWs due to their relatively low stacking fault energy, especially for GaP (30 meV/atom) [8], which can be easily overcome at typical NW synthesis temperatures. Planar crystal defects, such as TBs and stacking faults, can affect electron transport by acting as a carrier scattering source [9, 10], a recombination center [11-13] or a trap [14, 15]. Unwanted radiative or non-radiative recombination associated with mid-gap states can be detrimental to the efficiency of optoelectronic devices such as removing carriers from the desired recombination channel in lasers or LEDs or reducing carrier collection in photovoltaic cells. Understanding the potential effects of such defects on the electronic and optical properties of NWs is critical for NW optoelectronic devices.Here, we present structural and optical studies of GaP NWs combined with ab initio calculations to establish a structure-property relationship. Despite GaP being an indirect semiconductor, photoluminescence (PL) spectra of GaP NWs show optical transitions at energies lower than the fundamental band gap of bulk GaP. Transmission electron microscopy (TEM) analysis of NWs indicates that GaP is present in the zinc blende (ZB) phase along with the existence of TBs. We use a density functional theory (DFT) to establish a model of the 111 TB in GaP and propose an effective band diagram that explains the origin of sub-band gap optical transitions. II. METHOD A. Experimental detailsGaP NWs were grown on (111) Si by the self-assisted (seeded by a Ga droplet) selective-area epitaxy method using a multi-source ...

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Section: Resultsmentioning

confidence: 93%

Stacking defects in GaP nanowires: Electronic structure and optical properties

Gupta

Goktas

Rao

et al. 2019

Journal of Applied Physics

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“…Similar theoretical and experimental observations were made for pseudodirect wurtzite semiconductors in comparison to indirect zinc‐blende materials, e.g., for InP nanowires alloyed with Al, [ 27 ] or in wurtzite GaP nanowires, where strong many‐body excitonic effects or tensile uniaxial strain can explain the strong measured luminescence. [ 28–30 ]…”

Section: Resultsmentioning

confidence: 99%

“…Similar theoretical and experimental observations were made for pseudodirect wurtzite semiconductors in comparison to indirect zinc-blende materials, e.g., for InP nanowires alloyed with Al, [27] or in wurtzite GaP nanowires, where strong many-body excitonic effects or tensile uniaxial strain can explain the strong measured luminescence. [28][29][30] For a better understanding of the origin of the perturbationinduced enhancement of oscillator strengths for optical transitions in 2H-Ge we considered the effect of purely structural perturbations, and compared them to combined chemical and structural perturbations. Considering the results summarized in Figure 3 and Table 2, we can conclude that the influence of small structural perturbations is much weaker than the chemical effect, despite the fact that Si and Ge are isovalent.…”

Section: Energy Level [Ev]mentioning

confidence: 99%

Giant Optical Oscillator Strengths in Perturbed Hexagonal Germanium

Belabbes

Bechstedt

Botti

2022

Physica Rapid Research Ltrs

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By means of ab initio calculations we demonstrate that perturbed hexagonal germanium is a superior material for active optoelectronic devices in the infrared spectral region. Perfect lonsdaleite germanium is a pseudodirect semiconductor, with a direct fundamental band gap but almost vanishing optical transitions. Perturbing the system by replacing a germanium atom with a silicon atom in the primitive cell increases the oscillator strength at the onset gap by orders of magnitude, with a concurrent blue shift of the transition energies. This effect is mainly due to the increased s character of the lowest conduction band because of the perturbation‐induced wave function mixing. A structural distortion of pure lonsdaleite Ge can enhance as well optical oscillator strengths, but their magnitude significantly depends on the specific details of the resulting atomic geometry. In particular, moderate tensile uniaxial strain can induce an order inversion of the two lowest conduction bands, leading to an extremely efficient enhancement of the dipole matrix elements at the minimum gap. In general, chemical and/or structural perturbations are shown to make lonsdaleite germanium a suitable material for light emitting devices.

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“…These features were attributed to the presence of a direct band gap in wurtzite NWs. Strain, 16 alloying, 17 and excitonic effects 18 were then predicted to further enhance the optical oscillator strength in GaP NWs. The presence of uniaxial tensile strain along the c axis in wurtzite GaP NWs was predicted 16 to lead to a crossover between Γ 7c (which red-shifts with increasing strain) and Γ 8c (which blue-shifts under the same conditions), hence to a pseudodirect-to-direct transition in these systems.…”

Section: Resultsmentioning

confidence: 99%

Indirect to Direct Band Gap Transformation by Surface Engineering in Semiconductor Nanostructures

Califano

Zhou

2021

ACS Nano

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Indirect band gap semiconductor materials are routinely exploited in photonics, optoelectronics, and energy harvesting. However, their optical conversion efficiency is low, due to their poor optical properties, and a wide range of strategies, generally involving doping or alloying, has been explored to increase it, often, however, at the cost of changing their material properties and their band gap energy, which, in essence, amounts to changing them into different materials altogether. A key challenge is therefore to identify effective strategies to substantially enhance optical transitions at the band gap in these materials without sacrificing their intrinsic nature. Here, we show that this is indeed possible and that GaP can be transformed into a direct gap material by simple nanostructuring and surface engineering, while fully preserving its “identity”. We then distill the main ingredients of this procedure into a general recipe applicable to any indirect material and test it on AlAs, obtaining an increase of over 4 orders of magnitude in both emission intensity and radiative rates.

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Forbidden Band‐Edge Excitons of Wurtzite‐GaP: A Theoretical View

Cited by 17 publications

References 39 publications

Stacking defects in GaP nanowires: Electronic structure and optical properties

Stacking defects in GaP nanowires: Electronic structure and optical properties

Giant Optical Oscillator Strengths in Perturbed Hexagonal Germanium

Indirect to Direct Band Gap Transformation by Surface Engineering in Semiconductor Nanostructures

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