Temperature-dependent absorption measurements of excitons in GaN epilayers

Fischer, Arthur J.; Shan, Wei; Song, J. J.; Chang, Yia‐Chung; Horning, R.D.; Goldenberg, B.

doi:10.1063/1.119761

Cited by 120 publications

(73 citation statements)

References 19 publications

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“…17 for hexagonal GaN. A pronounced peak in <ε 1 > and minimum in <ε 2 > at 3.40 eV marks the superposition of the A and B excitonic transitions at the fundamental band gap of GaN [18,19]. At the high-energy side of this peak a shoulder appears in <ε 1 > which is tentatively assigned to the C excitonic transition.…”

Section: Resultsmentioning

confidence: 95%

Composition Dependence of the Band Gap Energy of In_xGa_1−xN Layers on GaN (x≤0.15) Grown by Metal-Organic Chemical Vapor Deposition

Wagner

Ramakrishnan

Behr

et al. 1999

MRS Internet j. nitride semicond. res.

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We report on the composition dependence of the band gap energy of strained hexagonal In x Ga 1-x N layers on GaN with x≤0.15, grown by metal-organic chemical vapor deposition on sapphire substrates. The composition of the (InGa)N was determined by secondary ion mass spectroscopy. High-resolution X-ray diffraction measurements confirmed that the (InGa)N layers with typical thicknesses of 30 nm are pseudomorphically strained to the in-plane lattice parameter of the underlying GaN. Room-temperature photoreflection spectroscopy and spectroscopic ellipsometry were used to determine the (InGa)N band gap energy. The composition dependence of the band gap energy of the strained (InGa)N layers was found to be given by E G (x)=3.43-3.28⋅x (eV) for x≤0.15. When correcting for the strain induced shift of the fundamental energy gap, a bowing parameter of 3.2 eV was obtained for the composition dependence of the gap energy of unstrained (InGa)N.

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Section: Resultsmentioning

confidence: 95%

Composition Dependence of the Band Gap Energy of In_xGa_1−xN Layers on GaN (x≤0.15) Grown by Metal-Organic Chemical Vapor Deposition

Wagner

Ramakrishnan

Behr

et al. 1999

MRS Internet j. nitride semicond. res.

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“…These features are not only observed in ZnO, but have also been found in optical spectra of many partly ionic materials. [11][12][13][14] Theoretical considerations of EPC contributions to the DF can be found in Refs. [15][16][17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Optical properties of MgZnO alloys: Excitons and exciton-phonon complexes

Neumann

Cobet

Esser

et al. 2011

Journal of Applied Physics

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The characteristics of the excitonic absorption and emission around the fundamental bandgap of wurtzite Mg x Zn 1Àx O grown on c-plane sapphire substrates by plasma assisted molecular beam epitaxy with Mg contents between x ¼ 0 and x ¼ 0.23 are studied using spectroscopic ellipsometry and photoluminescence (PL) measurements. The ellipsometric data were analyzed using a multilayer model yielding the dielectric function (DF). The imaginary part of the DF for the alloys exhibits a pronounced feature which is attributed to exciton-phonon coupling (EPC) similar to the previously reported results for ZnO. Thus, in order to determine reliable transition energies, the spectral dependence is analyzed by a model which includes free excitonic lines, the exciton continuum, and the enhanced absorption due to EPC. A line shape analysis of the temperature-dependent PL spectra yielded in particular the emission-related free excitonic transition energies, which are compared to the results from the DF line-shape analysis. The PL linewidth is discussed within the framework of an alloy disorder model.

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“…In low temperature absorption measurements three exciton lines (caused by three offset valence bands in wurtzite semiconductors) are observed. 18 When the temperature is raised the exciton lines broaden and, at room temperature, are hidden by the fundamental band-band absorption.…”

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confidence: 99%

Field-dependent charge carrier dynamics in GaN: Excitonic effects

Lagemaat

Vanmaekelbergh

Kelly

2004

Applied Physics Letters

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The electric-field dependence of the charge-carrier dynamics in GaN was studied by measuring excitation spectra of the sub-band-gap (yellow) luminescence as a function of bias using a Schottky junction formed at the interface between the semiconductor and an electrolyte solution. At large bias, the contribution of free electrons and holes to the photoluminescence is significantly reduced due to the dead-layer effect. As a result, striking features are revealed in the spectra close to the fundamental absorption. These features are attributed to exciton decay via yellow luminescence Electrons and holes, generated by light within the depletion layer of a Schottky diode, are effectively separated by the electric field and the minority carriers are collected at the interface. Minority carriers created within a diffusion length of the inner edge of the depletion layer can also reach the junction; 1 if they are transferred across the interface one observes photocurrent in the external circuit. Only those carriers created by light with a penetration depth ͑1/␣͒ which is larger than the sum of the minority carrier diffusion length L and the thickness of the space charge layer W will recombine, either nonradiatively or radiatively. The intensity of the emitted light I PL is given by:where 0 is the absorbed photon flux and is the ratio of the rate of radiative recombination to the total recombination rate. Many systems have been shown to conform to the "dead-layer model." 2-4Among the III-V semiconductors GaN is rather exceptional in that its exciton binding energy is large ͑ജ25 meV͒. [5][6][7][8] The formation of strongly bound electronhole pairs might be expected to influence the charge-carrier dynamics within the space-charge layer of an illuminated Schottky diode. In the present work we have used photoluminescence and photocurrent measurements on the Schottky junction formed at a semiconductor/solution interface to study excitonic effects in the field-dependent dynamics of carriers in n-type GaN epitaxial layers. We report an anomalous peak in the onset of the excitation spectrum of the subband-gap luminescence indicating enhanced emission at large band bending. We argue that this effect is due to a contribution from exciton absorption which is observed because of two reasons: the large binding energy of excitons and the suppression of emission from free carriers as a result of the dead-layer effect.The GaN epitaxial layers were grown by MOCVD on sapphire substrates using a 30 nm AlN buffer layer to reduce stress. 9 The layers were co-doped with Si. The density of uncompensated donors was 6 ϫ 10 17 cm −3 . Ohmic contacts were deposited by microwave sputtering of Ti/ Al/ Ni/ Au ͑15/ 300/ 40/ 200 nm͒. The ͑0001͒ Ga-terminated surface was exposed to solution.9 A standard three electrode cell was used for the electrochemical experiments. All potentials are reported with respect to the standard calomel electrode. Reproducible clean electrode surfaces were obtained by dipping in HCl before each experiment. The electrolyte fo...

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Temperature-dependent absorption measurements of excitons in GaN epilayers

Cited by 120 publications

References 19 publications

Composition Dependence of the Band Gap Energy of In_xGa_1−xN Layers on GaN (x≤0.15) Grown by Metal-Organic Chemical Vapor Deposition

Composition Dependence of the Band Gap Energy of In_xGa_1−xN Layers on GaN (x≤0.15) Grown by Metal-Organic Chemical Vapor Deposition

Optical properties of MgZnO alloys: Excitons and exciton-phonon complexes

Field-dependent charge carrier dynamics in GaN: Excitonic effects

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Temperature-dependent absorption measurements of excitons in GaN epilayers

Cited by 120 publications

References 19 publications

Composition Dependence of the Band Gap Energy of InxGa1−xN Layers on GaN (x≤0.15) Grown by Metal-Organic Chemical Vapor Deposition

Composition Dependence of the Band Gap Energy of InxGa1−xN Layers on GaN (x≤0.15) Grown by Metal-Organic Chemical Vapor Deposition

Optical properties of MgZnO alloys: Excitons and exciton-phonon complexes

Field-dependent charge carrier dynamics in GaN: Excitonic effects

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Composition Dependence of the Band Gap Energy of In_xGa_1−xN Layers on GaN (x≤0.15) Grown by Metal-Organic Chemical Vapor Deposition

Composition Dependence of the Band Gap Energy of In_xGa_1−xN Layers on GaN (x≤0.15) Grown by Metal-Organic Chemical Vapor Deposition