We analyzed the intrinsic defects and the n-type-carrier concentration generated by nitrogen ion implantation in n-type GaN by deep-level-transient spectroscopy and by capacitance–voltage measurements, respectively. The samples were grown on sapphire by metalorganic vapor-phase epitaxy. Nitrogen implantation with different ion doses and postimplantation rapid-thermal annealing (RTA) were investigated. We observed a growing n-type-carrier concentration and increasing defect concentration with increasing nitrogen ion implantation doses. After RTA the concentration of free carriers and deep levels as found in the as-grown state are restored. We also address contrarily seeming results from measurements of sheet resistance after N implantation published recently.

Trace impurities of vanadium in Lely-grown silicon carbide single crystals have been detected by their strong, polytype-specific photoluminescence in the 1.3-1.5 mym near-infrared spectral rang, as well as by infrared absorption. A high 0/A high-, and possibly also as a deep donor. The role of vanadium as minority-carrier lifetime killer in SiC-based optoelectronic devices is suggested from these data

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The energy structure and the carrier relaxation in self-assembled InAs/GaAs quantum dots (SADs) is investigated by photoluminescence excitation spectroscopy (PLE) and photoluminescence (PL) at resonant excitation (below the GaAs and the wetting layer bandgap). In PLE measurements we find a clear resonance from the first excited hole state as well as resonances from a relaxation via different phonons. From a comparison of the PL-rise times in time resolved spectroscopy, we conclude on a fast electron relaxation (⩽50 ps) and a slow hole relaxation with a time constant of about 400 ps. Different relaxation paths are observed in the InAs/GaAs quantum dot system and allow us to identify the hole relaxation in the SADs as multiphonon assisted tunneling. The PL-decay time in the SADs after resonant excitation (about 600 ps) is attributed to the lifetime of the quantum dot exciton. In agreement with theoretical predictions, we find a constant lifetime of about 600 ps for temperatures below 50 K and a linear increase of the lifetime between 50 and 100 K with a slope of 26 ps/K.

We present highly resolved photoluminescence (PL) and absorption spectra of the internal d-dshell transitions at Fe + in InP and the related phonon sidebands. By use of the Fourier-transforminfrared technique, the signal-to-noise ratio (SNR) is improved by about two orders of magnitude as compared to conventional dispersive techniques. Thus we are able to resolve new fine structure in the zero-phonon lines of Fe + in both absorption and PL. This fine structure is identified as shift induced by different iron isotopes. A better SNR also reveals several new features in PL spectra of the phonon sidebands. In absorption measurements Fe + related spectra in the energetic range of 2800 to 3400 cm ' ( =0.35 -0.4 eV) are recorded, which can be partly attributed to anti-Stokes lines of phonon coupling in emission. Additional peaks at 3103 and 3117 cm ' are interpreted as transitions from the 'E ground state to an excited state of the 'T2 manifold of Fe +.

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