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Microscopic Luminescence Properties of ZnO and ZnO Based Heterostructures

100%

Bertram F., Christen J.

Acta Physica Polonica A

2006

vol. 110

issue 2

103-110

The optical properties of excitonic recombinations in ZnO are investigated by spatially and spectrally resolved cathodoluminescence measurements. The relevance of cathodoluminescence microscopy as a spatially resolved luminescence technique as a simple but very powerful characterization method is stressed out in discussions of a wide variety of appropriate examples. A thorough discussion of the various features of the cathodoluminescence of an undoped ZnO bulk crystal, epitaxially grown ZnO and MgZnO/ZnO/MgZnO quantum well structure is given. Particular attention is devoted to the impact of the internal electrical fields, e.g. the Franz-Keldysh effect in ZnO. Furthermore, this study focuses on the spectral variations as a function of depth to the interface in ZnO homo- and heterostructures. Our aim is to establish the nature of the optical transitions influenced by internal fields, defects and impurity doping in ZnO/GaN and ZnO/ZnO interfaces. This review covers also the vertical transport, diffusion and capture of carriers in a MgZnO/ZnO/MgZnO quantum well structure.

Excitons and Phonons in GaN. Magnetooptical and Spatially Resolved Investigations

61%

Hoffmann A., Eckey L., Siegle H., Kaschner A., Christen J., Bertram F., Liu Q.

Acta Physica Polonica A

1998

vol. 94

issue 2

125-137

A comprehensive study of the direct photoluminescence from free-exciton states in GaN using polarization-dependent and magnetooptical measurements is presented. We measured and identified fine-structure splittings in the n=1 state of the A-exciton. From the magnetoluminescence data obtained in fields up to 15 T we determined the g-values of the conduction and valence bands parallel and perpendicular to the c-axis. Self-organized hexagonal GaN pyramids of 5 μm width and covered by six {11̲01} side facets were investigated by spatially resolved cathodoluminescence and micro-Raman spectroscopy. Beside a narrow luminescence peak at 355 nm, originating from the 2 μm thick GaN layer, an additional broad luminescence band was observed from the GaN pyramids around a wavelength of 357 nm. A strong energy shift is found along the {11̲01} pyramidal facets and directly visualized by monochromatic cathodoluminescence images and line scans. In GaN epilayers grown on GaAs substrates a series of sharp modes in the range between 60 cm^{-1} and 250 cm^{-1} for temperatures below 100 K was found. The intensities of these modes increased drastically with decreasing temperature. Raman excitation spectra showed a maximum between 514.5 nm and 568 nm. A comparison of spatially resolved investigations with that of intentionally doped GaN epilayers showed that the in-diffusion of As from the substrate plays an important role. Raman spectra as a function of external fields, like magnetic field and hydrostatic pressure, gave additional information about the defect type and the underlying scattering mechanism.

Optical Properties and Microstructure of InGaN Grown by Molecular Beam Epitaxy

42%

Böttcher T., Einfeldt S., Figge S., Kirchner V., Hommel D., Selke H., Ryder P., Bertram F., Riemann T., Christen J., Lunz U., Becker C.

Acta Physica Polonica A

1998

vol. 94

issue 2

260-264

The luminescence of In_{x}Ga_{1-x}N is studied for thick epitaxial layers and quantum wells. Using spatially resolved cathodoluminescence spectroscopy the commonly observed broad integral photoluminescence spectra were found to result from spectral and lateral inhomogeneous emission across the samples. Moreover, the integral photoluminescence and absorption spectra show different temperature dependences. The effects can be explained assuming fluctuations of the composition associated with a variation of the band gap.

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3 Acta Physica Polonica A

1 2006

2 1998

3 Bertram F.

3 Christen J.

1 Becker C.

1 Böttcher T.

1 Eckey L.

1 Einfeldt S.

1 Figge S.

1 Hoffmann A.

1 Hommel D.

1 Kaschner A.

1 Kirchner V.

1 Liu Q.

1 Lunz U.

1 Riemann T.

1 Ryder P.

1 Selke H.

1 Siegle H.

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Microscopic Luminescence Properties of ZnO and ZnO Based Heterostructures

Excitons and Phonons in GaN. Magnetooptical and Spatially Resolved Investigations

Optical Properties and Microstructure of InGaN Grown by Molecular Beam Epitaxy