The 3.466 eV Bound Exciton in GaN

Ḿonemar, B.; Chen, Weimin; Paskov, Plamen; Paskova, T.; Pozina, Galia; Bergman, J.P.

doi:10.1002/1521-3951(200111)228:2<489::aid-pssb489>3.3.co;2-e

Cited by 3 publications

(2 citation statements)

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“…In addition, towards lower energies one observes the L1 emission line in Fig. 2(b), whose origin is still under debate in the literature, ranging from a deep, over an ionized donor-bound exciton, to a neutral, shallow acceptor bound exciton [55][56][57][58].…”

Section: Resultsmentioning

confidence: 99%

Probing alloy formation using different excitonic species: The particular case of InGaN

Callsen

Butté

2019

2019 Compound Semiconductor Week (CSW)

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Since the early 1960s, alloys are commonly grouped into two classes, featuring bound states in the bandgap (I) or additional, non-discrete, band states (II). As a consequence, one can observe either a rich and informative zoo of excitons bound to isoelectronic impurities (I), or the typical bandedge emission of a semiconductor that shifts and broadens with rising isoelectronic doping concentration (II). Microscopic material parameters for class I alloys can directly be extracted from photoluminescence (PL) spectra, whereas any conclusions drawn for class II alloys usually remain indirect and limited to macroscopic assertions. Nonetheless, here, we present a comprehensive spectroscopic study on exciton localization in a so-called mixed crystal alloy (class II) that allows us to access microscopic alloy parameters. In order to exemplify our experimental approach we study bulk InxGa1−xN epilayers at the onset of alloy formation (0 ≤ x ≤ 2.4%) in order to understand the material's particular robustness to point and structural defects. Based on an in-depth PL analysis it is demonstrated how different excitonic complexes (free, bound, and complex bound excitons) can serve as a probe to monitor the dilute limit of class II alloys. From an x-dependent linewidth analysis we extract the length scales at which excitons become increasingly localized, meaning that they convert from a free to a bound particle upon alloy formation. Already at x = 2.4% the average exciton diffusion length is reduced to 5.7±1.3 nm at a temperature of 12 K, thus, detrimental exciton transfer mechanisms towards non-radiative defects are suppressed. In addition, the associated low temperature luminescence data suggests that a single indium atom does not suffice in order to permanently capture an exciton. The low density of silicon impurities in our samples even allows studying their local, indium-enriched environment at the length scale of the exciton Bohr radius based on impurity bound excitons. The associated temperature-dependent PL data reveals an alloying dependence for the exciton-phonon coupling. Thus, the formation of the random alloy can not only directly be monitored by the emission of various excitonic complexes, but also more indirectly via the associated coupling(s) to the phonon bath. Micro-PL spectra even give access to a forthright probing of silicon bound excitons embedded in a particular environment of indium atoms, thanks to the emergence of a hierarchy of individual, energetically sharp emission lines (full width at half maximum ≈ 300 µeV). Consequently, the present spectroscopic study allows us to extract first microscopic alloy properties formerly only accessible for class I alloys. * gordon.callsen@epfl.ch tronic centers (II) evokes the formation of mixed crystal alloys like, e.g., SiGe [14], GaAsP [15], InGaAs [16], AlGaAs [17], InGaN [18], AlGaN [19], CdSSe [20, 21], ZnSeTe [21], and MgZnO [22]. In these cases, no new electronic levels are formed in the bandgap, but rather in the bands themselves, a process often described a...

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Section: Resultsmentioning

confidence: 99%

Probing alloy formation using different excitonic species: The particular case of InGaN

Callsen

Butté

2019

2019 Compound Semiconductor Week (CSW)

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“…In addition, toward lower energies one observes the L1 emission line in Fig. 2(b), whose origin is still under debate in literature, ranging from a deep donor-bound exciton, over an ionized donor-bound exciton, to a neutral shallow acceptor-bound exciton [62][63][64][65].…”

Section: Fig 1 (A)mentioning

confidence: 97%

Probing Alloy Formation Using Different Excitonic Species: The Particular Case of InGaN

2019

View full text Add to dashboard Cite

Since the early 1960s, alloys are commonly grouped into two classes that feature either bound states in the band gap (I) or additional, nondiscrete band states (II). Consequently, one can observe either excitons bound to isoelectronic impurities or the typical band edge emission of a semiconductor that shifts and broadens with rising isoelectronic doping concentration. Microscopic parameters for class I alloys can directly be extracted from photoluminescence (PL) spectra, whereas any conclusions drawn for class II alloys usually remain limited to macroscopic assertions. Nonetheless, we present a spectroscopic study on exciton localization in a mixed-crystal alloy (class II) that allows us to access microscopic alloy parameters. In order to illustrate our approach, we study bulk In x Ga 1−x N epilayers at the onset of alloying (0 ≤ x ≤ 2.4%) in order to understand their robustness to point and structural defects. Through an indepth PL analysis it is demonstrated how different excitonic complexes (free, bound, and complex bound excitons) can serve as a probe to monitor the dilute limit of class II alloys. From an x-dependent linewidth analysis we extract the length scales at which excitons become increasingly localized, i.e., their conversion from a free to a bound particle upon alloy formation. Already at x ¼ 2.4% the exciton diffusion length is reduced to 5.7 AE 1.3 nm at a temperature of 12 K; hence, detrimental exciton transfer mechanisms toward nonradiative defects are suppressed. In addition, the associated low-temperature PL data suggest that a single indium atom cannot permanently capture an exciton. The low density of silicon impurities in our samples even allows studying their local indium-enriched environment at the scale of the exciton Bohr radius based on impurity bound excitons. The associated temperature-dependent PL data reveal an alloying dependence for the exciton-phonon coupling. Thus, the formation of the random alloy can not only be monitored by the emission of various excitonic complexes, but also more indirectly via the associated coupling(s) to the phonon bath. Micro-PL spectra even give access to a probing of silicon bound excitons embedded in a particular environment of indium atoms thanks to the emergence of a series of individual and energetically sharp emission lines (full width at half maximum ≈300 μeV). Consequently, the present study allows us to extract microscopic properties formerly mostly only accessible for class I alloys.

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Luminescence properties of defects in GaN

Reshchikov¹,

Morkoç̌²

2005

Journal of Applied Physics

1,782

118

1,653

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Gallium nitride ͑GaN͒ and its allied binaries InN and AIN as well as their ternary compounds have gained an unprecedented attention due to their wide-ranging applications encompassing green, blue, violet, and ultraviolet ͑UV͒ emitters and detectors ͑in photon ranges inaccessible by other semiconductors͒ and high-power amplifiers. However, even the best of the three binaries, GaN, contains many structural and point defects caused to a large extent by lattice and stacking mismatch with substrates. These defects notably affect the electrical and optical properties of the host material and can seriously degrade the performance and reliability of devices made based on these nitride semiconductors. Even though GaN broke the long-standing paradigm that high density of dislocations precludes acceptable device performance, point defects have taken the center stage as they exacerbate efforts to increase the efficiency of emitters, increase laser operation lifetime, and lead to anomalies in electronic devices. The point defects include native isolated defects ͑vacancies, interstitial, and antisites͒, intentional or unintentional impurities, as well as complexes involving different combinations of the isolated defects. Further improvements in device performance and longevity hinge on an in-depth understanding of point defects and their reduction. In this review a comprehensive and critical analysis of point defects in GaN, particularly their manifestation in luminescence, is presented. In addition to a comprehensive analysis of native point defects, the signatures of intentionally and unintentionally introduced impurities are addressed. The review discusses in detail the characteristics and the origin of the major luminescence bands including the ultraviolet, blue, green, yellow, and red bands in undoped GaN. The effects of important group-II impurities, such as Zn and Mg on the photoluminescence of GaN, are treated in detail. Similarly, but to a lesser extent, the effects of other impurities, such as C, Si, H, O, Be, Mn, Cd, etc., on the luminescence properties of GaN are also reviewed. Further, atypical luminescence lines which are tentatively attributed to the surface and structural defects are discussed. The effect of surfaces and surface preparation, particularly wet and dry etching, exposure to UV light in vacuum or controlled gas ambient, annealing, and ion implantation on the characteristics of the defect-related emissions is described.

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The 3.466 eV Bound Exciton in GaN

Cited by 3 publications

References 0 publications

Probing alloy formation using different excitonic species: The particular case of InGaN

Probing alloy formation using different excitonic species: The particular case of InGaN

Probing Alloy Formation Using Different Excitonic Species: The Particular Case of InGaN

Luminescence properties of defects in GaN

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