Morphology of luminescent GaN films grown by molecular beam epitaxy

Trager‐Cowan, C.; O’Donnell, K. P.; Hooper, S. E.; Foxon, C.T.

doi:10.1063/1.116714

Cited by 39 publications

(12 citation statements)

References 4 publications

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“…1 A second broad band centered at 2.9 eV ͑blue band͒ is often observed in cathodoluminescence ͑CL͒ and photoluminescence ͑PL͒ spectrum of undoped ͑nominally n-type͒ and Sidoped GaN. [2][3][4][5][6][7][8][9] The 2.9 eV band was attributed to point defects, which are either relatively homogeneously distributed 2 or concentrated in the hillocks. 3 Variation of the CL intensity with time was observed by Toth et al and attributed to electromigration of H and O atoms, as well as to competition between different recombination channels.…”

Section: Introductionmentioning

confidence: 99%

Photoluminescence band near 2.9 eV in undoped GaN epitaxial layers

Reshchikov

Shahedipour

Korotkov

et al. 2000

Journal of Applied Physics

109

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The broad photoluminescence band with a maximum at about 2.9 eV widely observed in undoped epitaxial GaN is studied as a function of temperature and excitation intensity. We attribute the band to transitions from a shallow donor to a deep localized acceptor. The zero-phonon transition for this band is at 3.098 eV as determined from the fine structure at low temperatures. A local vibrational mode in the ground state with an energy of 36 meV is found.

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Section: Introductionmentioning

confidence: 99%

Photoluminescence band near 2.9 eV in undoped GaN epitaxial layers

Reshchikov

Shahedipour

Korotkov

et al. 2000

Journal of Applied Physics

109

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“…In the latter case, only a very weak or even no luminescence intensity was measured with our set-up. The physical reason for that can be explained by an efficient capture of tip-emitted electrons in defect sites -a process which occurs non-radiatively in agreement with conventional cathodoluminescence experiments [4].…”

Section: Resultsmentioning

confidence: 72%

“…Using standard formulas in semiconductor physics given in [19], the mean free path falls in the 100 nm range as a result of the high concentration of free carriers in the GaN layers. On the other hand, as already pointed out in [4] and [7] and expected from the aforementioned model for STM-excited luminescence, a high recombination site density in near-surface regions or at defects may substantially enhance the lateral resolution in these experiments. A first indication that the surface properties might indeed play an important role has recently been inferred from a study of STM-excited luminescence of AlGaAs samples covered with a 6-nm layer of GaAs.…”

Section: The Modelmentioning

confidence: 88%

“…The local optical properties of group-III nitrides have been scrutinized by cathodoluminescence measurements using electrons in the keV energy range. These results show that almost the entire luminescence originates from single-crystalline regions, where the most light-active material is found close to the surface of the crystallites [4]. Unfortunately, the lateral resolution of cathodoluminescence studies is limited to approximately 500 nm.…”

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confidence: 93%

“…A first approach has been to study the surface morphology of thin GaN films grown by molecular beam epitaxy (MBE) on sapphire substrates using atomic force microscopy (AFM). These measurements clearly reveal the presence of individual columns or crystallites having sizes in the µm range [4,5]. Scanning tunneling microscope (STM) and transmission electron microscope (TEM) investigations have been carried out to examine the structural properties of GaN layers grown by low-pressure chemical vapor deposition (LP-CVD) techniques [6].…”

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confidence: 99%

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STM-excited and spectrally resolved luminescence of epitaxial GaN and AlGaN layers grown by MBE

Ortsiefer

Liebheit

Schwartzkopff

et al. 1998

Applied Physics A: Materials Science & Processing

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We present spectrally resolved luminescence data of wide-bandgap group-III nitride layers grown by molecular beam epitaxy on sapphire substrates. The luminescence is locally excited by electrons provided by the tip of a scanning tunneling microscope (STM) operated at room temperature. Nominally undoped, the group-III nitride layers naturally show n-type character, thus guaranteeing sufficient electrical conductivity for the STM studies. Luminescence spectra recorded with the STM typically reveal the near-bandgap signal peaking at ≈ 3.4 eV. By incorporating Mg with a concentration of 10 20 cm −3 , the background n-type character can be overcompensated, giving rise to a pronounced radiative transition into the acceptor level located at ≈ 3.2 eV. The absolute peak intensities, however, markedly depend on the site of excitation at the sample surface. This effect allows to distinguish unequivocally between high-quality and defect-rich film regions, also offering the opportunity to correlate nearsurface optical properties with morphological features. By adding 10% Al, the resulting crystal alloy exhibits a wider energy-band gap which is reflected in a blue shift of the respective STM-excited luminescence signal.Direct bandgap group-III nitrides, covering a spectral range from 1.9 eV (InN) or 3.4 eV (GaN) up to 6.2 eV (AlN), have great potential in the realm of optoelectronics. The possibility of preparing ternary crystal alloys makes these materials most attractive for bandgap engineering. Great efforts have been devoted to the development of light-emitting devices, culminating in the successful demonstration of a laser diode [1]. Further applications of this family of materials include the absorption of ultraviolet radiation using appropriate sensor devices [2].Notwithstanding the remarkable efficiency of blue lightemitting devices based on GaN, the epilayers usually exhibit a high density of different types of dislocations, in- * On leave to: volving low-angle grain boundaries associated with crystalline columns [3]. Several techniques have been utilized so far in characterizing group-III nitride layers, including Xray diffraction, photoluminescence, Hall measurements, and cathodoluminescence. However, there is still a need to examine the initial stage of nucleation and its impact on subsequent layer growth. Furthermore, there is great interest in gaining a deeper insight into the detailed material composition and the related optical properties, particularly at the nanometer scale. A first approach has been to study the surface morphology of thin GaN films grown by molecular beam epitaxy (MBE) on sapphire substrates using atomic force microscopy (AFM). These measurements clearly reveal the presence of individual columns or crystallites having sizes in the µm range [4,5]. Scanning tunneling microscope (STM) and transmission electron microscope (TEM) investigations have been carried out to examine the structural properties of GaN layers grown by low-pressure chemical vapor deposition (LP-CVD) techniques [6]. The local ...

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