Free and bound excitons in thin wurtzite GaN layers on sapphire

Merz, C. J.; Kunzer, M.; Kaufmann, U.; Akasaki, Isamu; Amano, Hiroshi

doi:10.1088/0268-1242/11/5/010

Cited by 112 publications

(46 citation statements)

References 31 publications

(38 reference statements)

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“…described by the empirical Varshni model 59 or is in more detail modeled by Vina et al 60,61 who apply the Bose-Einstein model and obtain a more reliable description for lower temperatures. The bound excitons in GaN also experience such a red shift of their luminescences but due to their localization this effect is weaker 34,54,55 and cannot clearly be resolved in the analyzed temperature window for a GaN:Mg sample with spectral linewidths of ∼ 5 meV. However, the different evolution of the intensity and the spectral position of the bound and free excitonic transitions still allows their identification.…”

Section: Determination Of the Activation Energiesmentioning

confidence: 99%

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Optical signature of Mg-doped GaN: Transfer processes

et al. 2012

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Mg doping of high quality, metal organic chemical vapor deposition grown GaN films results in distinct traces in their photoluminescence and photoluminescence excitation spectra. We analyze GaN:Mg grown on sapphire substrates and identify two Mg related acceptor states, one additional acceptor state and three donor states which are involved in the donor acceptor pair band transitions situated at 3.26 eV -3.29 eV in GaN:Mg. The presented determination of the donor acceptor pair band excitation channels by photoluminescence excitation spectroscopy in conjunction with temperature dependent photoluminescence measurements results in a direct determination of the donor and acceptor binding, localization, and activation energies which is put into a broader context based on Haynes's rule. Furthermore, we analyze the biexponential decay dynamics of the photoluminescence signal of the acceptor and donor bound excitons. As all observed lifetimes scale with the localization energy of the donor and acceptor related bound excitons, defect and complex bound excitons can be excluded as their origin. Detailed analysis of the exciton transfer processes in the close energetic vicinity of the GaN bandedge reveals excitation via free and bound excitonic channels but also via an excited state as resolved for the deepest localized Mg related acceptor bound exciton. For the two Mg acceptor states we determine binding energies of 164±5 meV and 195±5 meV which is in good agreement with recent density functional theory results. This observation confirms and quantifies the general dual nature of acceptor states in GaN based on the presented analysis of the photoluminescence and photoluminescence excitation spectra.

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Section: Determination Of the Activation Energiesmentioning

confidence: 99%

“…Zn 51,54 or Be. and τ D2,A2 which is further supported by the determined activation energies E act from section IV.…”

mentioning

confidence: 99%

Optical signature of Mg-doped GaN: Transfer processes

et al. 2012

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“…A number of authors have shown that this strain is clearly evidenced by shifts in the photoluminescence ͑PL͒, photoreflectance ͑PR͒, and reflectance ͑R͒ line positions. [2][3][4][5][6][7][8][9][10] It was shown in Ref. 9 that the energy of the free exciton associated with the top valence band (E A ) varies linearly with the in-plane and axial components of the strain tensor.…”

Section: Introductionmentioning

confidence: 99%

Strain variation with sample thickness in GaN grown by hydride vapor phase epitaxy

Reynolds

Jogai

Hoelscher

et al. 2000

Journal of Applied Physics

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High quality GaN crystals can be grown on sapphire by hydride vapor phase epitaxy. The thermal expansion mismatch between sapphire and GaN produces strain in the GaN crystal as it is cooled from the growth temperature to room temperature. The strain is evidenced by shifts in the photoluminescence and reflectance line positions. By analyzing the surface strain as the crystal thickness is increased, the thickness required to obtain zero surface strain can be estimated. This structure might provide a lattice matched and thermally matched substrate for further epitaxial growth of GaN.

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“…Because of the lack of high-quality bulk crystals with large size, GaN are usually grown on foreign substrates including sapphire, SiC, silicon, and so on [1][2][3]. This heteroepitaxy gives rise to a homogeneous strain field mainly in consequence of the thermal expansion mismatch.…”

mentioning

confidence: 99%

Degenerate four‐wave mixing spectroscopy of GaN films on various substrates

Ishiguro

Toda

Adachi

et al. 2006

Physica Status Solidi (b)

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We have carried out time-integrated and spectrally-resolved four-wave mixing (FWM) measurements to study the effects of built-in strain within GaN films on their exciton structures and on their coherent dynamics. Precise values for exciton energies, linewidths, and oscillation periods of quantum beats were presented. Remarkable phase shifts of the quantum beats were observed in the GaN films on a-sapphire, suggesting the exciton -exciton interaction caused by the reduction of the crystal symmetry.The effects of strain-fields in semiconductor have been a subject of interest for many years. Because of the lack of high-quality bulk crystals with large size, GaN are usually grown on foreign substrates including sapphire, SiC, silicon, and so on [1][2][3]. This heteroepitaxy gives rise to a homogeneous strain field mainly in consequence of the thermal expansion mismatch. Such built-in strain produces the change in the lattice parameters and, in some cases, in the crystal symmetry, giving rise to an intrinsic modification of the electric band structure. Since the degree of built-in strain significantly varies with the substrate materials, the combination of various substrates offers favorable possibilities for the electric band engineering. The study of built-in strain effect is thus important for improving the device performance.In this work, we present the results obtained from degenerate four-wave mixing (FWM) measurements in GaN films grown on various substrates. Since the FWM signal increases nonlinearly with the oscillator strength, strong and well-separated spectral features associated with A-and B -excitons could be observed in each sample. As a consequence, we can determine the shifts of the exciton energies originating from the biaxial strain with high accuracy. In addition, FWM combined with an ultrashort pulse laser offers precise information about the Coulomb interactions of excitons in the presence of the strainfield. Remarkable phase shifts of the quantum beat signals resulting from the spin-dependent excitonexciton interaction was observed in the GaN on a-sapphire.GaN films were grown on the 6H-SiC, (1120) a-and (0001) c-planes of sapphire. These films were prepared by two-flow metal-organic chemical-vapor-deposition (MOCVD) with 40-50 nm thick buffer layers [4]. The free-standing 70 µm GaN was also prepared by two-flow MOCVD. The two-pulse FWM experiments in reflection geometry were performed using a frequency doubled, mode-locked tunable Ti:sapphire laser with the spectral width of 13 meV (FWHM). The excitation pulses with the same intensities were colinearly polarized and superimposed onto a sample surface using a lens (f = 200 mm).

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Free and bound excitons in thin wurtzite GaN layers on sapphire

Cited by 112 publications

References 31 publications

Optical signature of Mg-doped GaN: Transfer processes

Optical signature of Mg-doped GaN: Transfer processes

Strain variation with sample thickness in GaN grown by hydride vapor phase epitaxy

Degenerate four‐wave mixing spectroscopy of GaN films on various substrates

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