Molecular beam epitaxial growth of Si1−yCy alloys pseudomorphically strained on the (2×1) reconstructed Si(001) has been investigated as a function of growth conditions. An important question concerns the relation between substitutional and interstitial carbon incorporation, which has a large impact on electrical and optical properties of these layers. We show that the interstitial-to-substitutional carbon ratio is strongly influenced by the growth conditions, such as growth temperature and Si growth rate. Both reduction in growth temperature and increase of the overall growth rate lead to an increase in the substitutional-to-interstitial carbon ratio. However, these changes in growth conditions can also cause some deterioration in crystal quality. The carbon incorporation behavior is well described by first order kinetics.
The excitation and decay mechanisms of the Yb3+ intra-4f-shell emission are studied in n-type Mow-grown and p-type LPE grown InP:Yb layers by photoconductivity measurements, time-resolved photoluminescence, photoluminescence excitation and emission spectroscopy. Assuming a pseudodonor or pseudo-acceptor-like character of the isoelectronic Yb3+ T,, centre the temperature dependences of the 41-shell transition intensity and lifetime can be consistently explained. Models for the excitation and decay processes of the Yb3+ photoluminescence are proposed.
We report on optical investigations of a near-infrared luminescence band in hexagonal GaN with a single zero-phonon line (ZPL) at 1.1934 eV. It is attributed to the spin-forbidden internal d-d transition 'E (D)-A 2(F) of a defect with a d electronic configuration. This assignment is based on the observed Zeeman splittings, which agree with the ground and excited states being threefold and twofold degenerate, respectively. This interpretation is supported by the observed small full width at half maximum (FWHM) of the ZPL, the weak phonon sideband, and the weak temperature dependence of the luminescence band. With increasing temperature, the ZPL shifts towards lower energies but maintains its FWHM of about 200 peV up to 60 K. The observed luminescence lifetime of 65 ps indicates a strong mixing of the E (D) with the Tz(F) multiplet at slightly higher energies by spin-orbit interaction. Photoluminescence excitation spectra show intracenter absorption into the higher excited T, states at 1.62 and 2.8 eV in n-type samples, proving the defect to be in the luminescent charge state in n-type material. Thus, we propose Ti + as the luminescence center responsible for the 1.19-eV transition. Implications for the band o6'set between GaN and GaAs are discussed.
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