Negative spin-exchange splitting in the exciton fine structure of AlN

Feneberg, Martin; Romero, M. F.; Neuschl, Benjamin; Thonke, Klaus; Röppischer, Marcus; Cobet, Christoph; Esser, N.; Bickermann, Matthias; Goldhahn, R.

doi:10.1063/1.4790645

Cited by 22 publications

(21 citation statements)

References 24 publications

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“…The free exciton emission X n¼1 c-oriented dipole and thus be observable in detection perpendicular to the c-oriented sample surface. 27 From the first excited free exciton state X n¼2 A , the free exciton binding energy of 51.7 meV can be derived in agreement with earlier results. 12 Two donor bound exciton emission bands show up 13.4 meV and 28.6 meV below the X n¼1 A emission, where the deeper one is labeled Si o X and arises from excitons bound to neutral silicon donors.…”

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confidence: 81%

Direct determination of the silicon donor ionization energy in homoepitaxial AlN from photoluminescence two-electron transitions

Neuschl

Thonke

Feneberg

et al. 2013

Applied Physics Letters

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We report on the identification of a two-electron transition for the shallow donor silicon in homoepitaxial aluminum nitride (AlN). One c-oriented sample was analyzed by low temperature photoluminescence spectroscopy on multiple excitation spots. We find a unique correlation of one single emission band, 76.6 meV below the free excitonic emission, with the luminescence of excitons bound to neutral silicon proving the identity as a two-electron transition. The assignment is confirmed by temperature dependent photoluminescence investigations. We find a donor ionization energy of ð63:5 6 1:5Þ meV for silicon in AlN. V C 2013 AIP Publishing LLC.Recent interest in light emitting devices operating in the deep UV spectral region 1 is due to promising applications such as the deactivation of microorganisms by exposure to light with short wavelengths. Several research groups are working on light emitting diodes (LEDs) based on aluminum gallium nitride (AlGaN) fabricated on foreign substrates such as sapphire 2-4 or silicon carbide. 5 As a consequence, these structures suffer from high defect densities due to the lattice and thermal expansion coefficient mismatch between the substrate material and the epitaxial film, directly degrading the efficiency of the device. 6 One approach is to deposit the diode layer, with high Al content, directly on an AlN single crystal. This kind of substrate is promising for an improvement of the crystal quality, 7,8 and recently, well operating LEDs 9 and lasers 10,11 have been presented. Nevertheless, many fundamental properties such as the exact electronic structure for typical dopants are not known. Only recently, homoepitaxial AlN layers of good crystal quality became available allowing the proper identification of single bound excitonic emission bands. 12,13 However, for the mostly present donor silicon (Si), there is no agreement on the ionization energy. There is an ongoing discussion, whether Si Al undergoes a strong lattice relaxation and forms a deep DX center, where the dopant atom captures a second electron. Several theoretical studies predict DX center formation for Si Al , 14,15 whereas others find silicon to be a shallow donor in wurtzite AlN. 16,17 Experimentally, the majority of studies shows n-type conductivity after silicon doping, 18-24 although they find very different values for the ionization energy ranging from 86 to 570 meV. On the other hand, there are two detailed reports about DX center formation found by spectrally resolved photoconductivity and electron paramagnetic resonance. 25,26 In this letter, we present a detailed investigation of a homoepitaxially grown wurtzite AlN layer by means of temperature dependent photoluminescence (PL) spectroscopy. Exposure at multiple excitation spots and the temperature dependent behavior of the emission bands observed allow for an identification of a two-electron transition with shallow silicon donors involved. We further discuss the presented results in the framework of possible DX center formation.The sample under investigat...

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supporting

confidence: 81%

Direct determination of the silicon donor ionization energy in homoepitaxial AlN from photoluminescence two-electron transitions

Neuschl

Thonke

Feneberg

et al. 2013

Applied Physics Letters

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“…The fine structure of the free excitons related to the A transition has been reported recently. 14 In this work, a further splitting into excitons of 5 and 1 symmetries has been observed. Modeling yielded a negative spin-exchange interaction constant of j = −4 meV.…”

Section: Introductionmentioning

confidence: 64%

“…14 Photoluminescence was excited by ArF * excimer laser pulses with λ = 193 nm (E = 6.42 eV). The light source for reflectivity spectra was a D 2 lamp.…”

Section: Methodsmentioning

confidence: 99%

“…14 This fact is consistent with perturbation theoretical calculations. When calculating the relative oscillator strengths of the 1 and 5 excitons by using a 12 × 12 kp Hamiltonian 59 and setting the spin-exchange interaction to j = −4 meV, 14 we find that the 1 exciton has a very strong oscillator strength (close to 1) for E c, but it is zero for E ⊥ c. In contrast, the 5 exciton has an oscillator strength of zero for E c and only around 4 × 10 −4 for E ⊥ c. These results are in perfect agreement with our experimental findings, as 5 excitons can only show up in nonequilibrium experiments (luminescence) if E ⊥ c is probed.…”

Section: Emission Propertiesmentioning

confidence: 99%

“…For these calculations we took into account that the observed 7+ exciton resonance energy corresponds to the 1 exciton symmetry, and the degenerate 7+ energy position is −3j/2 = 6 meV higher in energy. 14 The value for j = −4 meV is taken to be independent of the temperature, while values of 9 and 7− excitons are used without further corrections. The values for cf and so are only slightly different from our previously reported parameter set based on thin epitaxial c-plane layers analyzed at room temperature.…”

Section: Dielectric Function Around the Band Gapmentioning

confidence: 99%

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Anisotropic absorption and emission of bulk(11¯00)AlN

et al. 2013

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The intrinsic anisotropic optical properties of wurtzite AlN are investigated in absorption and emission. Full access to the anisotropy of the optical response of the hexagonal material is obtained by investigating the (1100) plane of a high-quality bulk crystal allowing electric field E polarization perpendicular (E ⊥ c) and parallel (E c) to the optical axis c. Spectroscopic ellipsometry yields the ordinary (ε ⊥ ) and extraordinary (ε ) dielectric functions (DFs) from 0.58 up to 20 eV. The comparison of the experimental data with recently calculated DFs demonstrates that Coulomb interaction has a strong impact not only on the spectral dependence around the fundamental absorption edge but also on the high-energy features usually discussed in terms of van Hove singularities. The fits of the second-order derivatives of ε and ε ⊥ provide the transition energies for the main features in this range. The DFs close to the fundamental absorption edge, dominated by free excitons, exciton-phonon complexes, and the exciton continuum, are independently confirmed by reflectivity and synchrotron-based photoluminescence excitation studies. Values for the band gaps, the crystal field ( cf = −221 ± 2 meV), and spin-orbit splittings ( so = 13 ± 2 meV) are obtained. Furthermore, we obtain accurate values for the static dielectric constants of ε S⊥ = 7.65 and ε S = 9.21, entering, e.g., the calculations of exciton binding energies. Photoluminescence is used to investigate the emission properties of the same sample.

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A Combination of Ion Implantation and High‐Temperature Annealing: Donor–Acceptor Pairs in Carbon‐Implanted AlN

Peters

Spende

Wolter

et al. 2023

Physica Status Solidi (a)

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Herein, carbon‐implanted high‐temperature annealed (HTA) AlN layers are analyzed and donor–acceptor pair (DAP) transitions probably between the two most abundant impurities, carbon and oxygen, are identified. Both are regarded as the main, hard‐to‐avoid impurities in crystal growth. Oxygen is believed to lead to absorption in the deep UV below a wavelength of 250 nm. In contrast, carbon is the most likely candidate to be responsible for a distinct absorption band around 265 nm. This interpretation has recently been challenged. In this study, carbon‐implanted and HTA AlN layers with ion fluences above 8.1 × 1015 cm−2 are analyzed using low‐temperature and time‐resolved cathodoluminescence spectroscopy. Due to the high concentration of oxygen inside the AlN, as a result of the HTA process, a DAP transition between a most likely carbon‐related acceptor and ON is observed. The measured temperature‐ and power‐dependent blueshift of the peak emission energy as well as the luminescence transients can be clearly explained by a continuous change from a DAP transition at low temperature to a free electron to acceptor transition with increasing temperature. The findings are supported by a configurational coordinate model that describes the measured behavior qualitatively.

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Negative spin-exchange splitting in the exciton fine structure of AlN

Cited by 22 publications

References 24 publications

Direct determination of the silicon donor ionization energy in homoepitaxial AlN from photoluminescence two-electron transitions

Direct determination of the silicon donor ionization energy in homoepitaxial AlN from photoluminescence two-electron transitions

Anisotropic absorption and emission of bulk(11¯00)AlN

A Combination of Ion Implantation and High‐Temperature Annealing: Donor–Acceptor Pairs in Carbon‐Implanted AlN

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