A. Dörnen

Low pressure MOVPE of GaN and GaInNGaN heterostructures

Abstract GaN single layers and GaInN GaN heterostructures have been grown by low pressure metalorganic vapor phase epitaxy on sapphire substrates. We found best growth conditions and the highest growth rate for GaN to be at about 1000°C, whereas the growth rate decreased for both, higher and lower temperatures. In contrast, GaInN with a significantly high In content could only be grown at lower temperatures around 700°C. Besides growth temperature and reactor pressure, the composition of the carrier gas was found to play an important role: the In incorporation rate is about doubled when reducing the hydrogen/nitrogen ratio. GaInN GaN quantum wells show even higher In contents compared to bulk layers.

Movpe of Rare Earth Doped III-V Semiconductors

Different III-V compound semiconductors have been doped with the rare earth (RE) elements Yb, Er, and Tm using atmospheric pressure metalorganic vapor phase epitaxy. Best results have been obtained using the novel metalorganic compounds tris-isopropyl-cyclopentadienyl-RE as precursors which have an acceptable vapor pressure and can be used as liquids at bubbler temperatures of 60°-90°C. Only Yb has been found to occupy a regular lattice site in InP, whereas the other RE show complex optical spectra because of their incorporation in form of different centers and clusters.

Vibrational mode nitrogen and carbon isotope shifts on the N1(0.746 eV) photoluminescence spectrum in silicon

Abstract We observe 14N, 15N and 12C, 13C isotope shifts on a local mode with h ω = 122.9 meV in the vibronic sideband of the N1 (0.746 eV) photoluminescence line. This comfirms our previous conclusion that the optical defect incorporates nitrogen and carbon. In addition, the energy of the mode and the nitrogen isotope shift are close to those of the 963 cm-1 IR vibrational absorption line of nitrogen in silicon. These results, in conjunction with Zeeman and uniaxial stress data, suggest a microscopic model of the defect involving a carbon modified trigonally distorted substitutional nitrogen atom. Reported are also four other defect spectra depending on both nitrogen and carbon implantation.

Complexing of nitrogen with carbon and oxygen in silicon: photoluminescence studies

We study interactions of nitrogen with carbon and oxygen in crystalline silicon by photoluminescence spectroscopy. Such processes manifest themselves in five photoluminescence lines in the spectral region around 1.6 μm emerging after nitrogen and carbon implantations and furnace annealing with 550° C optimum temperature. Nitrogen and carbon isotope shifts of the lines confirm the incorporation of these atomic species in the optical defects. Nitrogen-oxygen interactions are demonstrated by differences in the lines’ appearance between oxygen-lean float-zone and oxygen-rich pulled silicon starting materials. The data suggests similar basic nitrogen-carbon units in all five defects.

Nitrogen-Carbon Interactions in Optical Defects in Silicon

We report five photoluminescence lines N1 through N5 in silicon which emerge after sequential nitrogen and carbon implantation. Studied is in particular the 0.7456 eV (N1) electronic-vibronic spectrum. Single nitrogen and carbon atoms in the defect are identified by isotope shifts of the no-phonon transition and of a local mode satellite with vibration quantum energy ħω= 122.9 meV. Uniaxial stress or Zeeman measurements yield monoclinic I (C 1h ) or trigonal (C 3v ) symmetry, respectively, of the optical defect. Comparing the energy of the local mode and its isotope effects with recent literature data on the nitrogen 963 cm −1 IR vibrational absorption line we discuss a defect model involving a substitutional nitrogen atom modified by an interstitial carbon atom.

Optical Investigation of Strained-Layer GaInAs/GaInAsP Heterostructures

We performed low temperature photocurrent and photoluminescence excitation spectroscopy on tensile and compressively strained Ga x In 1-x As/GaInAsP quantum well layers to determine the band offset of the heterojunction (0.3 X Ga m 0 for X Ga = 0.31 to about 0.45 m 0 for X Ga = 0.55.

Excitation Spectroscopy on Silicon Using Color Center Lasers Study of the Thermally Induced P Line (0.767eV) Defect

Recently developed tunable color center lasers allow to extend the experimental technique of excitation spectroscopy to the 1–2 μm region. This spectral range is of special interest for the study of luminescent defects in silicon. We discuss the color center laser systems available at present and their application to defect spectroscopy. As an example, results on the 0.767 eV (P line) defect in silicon are presented. Excitation spectroscopy reveals several high lying excited electronic states. They are interpreted as effective—mass—like states of a pseudo-donor with an ionization energy of 34.3 meV.