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.

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.

Articles you may be interested inInfluence of intrinsic strain on the surface acoustic wave-induced birefringence in InGaAs-GaAs and InGaAsP-InP multiple-quantum-well optical modulators Appl. Phys. Lett. 82, 1535 (2003); 10.1063/1.1559645 Forbidden transitions and the effective masses of electrons and holes in In 1−x Ga x As/InP quantum wells with compressive strain J. Appl. Phys. 93, 951 (2003); 10.1063/1.1527709Magnetoabsorption spectra of intraexcitonic transitions in GaAs-(Ga,Al)As semiconductor quantum wells Modeling and analysis of photomodulated reflectance and double crystal x-ray diffraction measurements of tensilely strained InGaAs/InGaAsP quantum well structures Low-temperature ͑1.8 K͒ magneto-optical absorption experiments have been performed on two tensile strained In 1Ϫx Ga x As/InP multiple-quantum-well samples. By using derivative spectra and the effective-mass equation of a quasi-two-dimensional exciton, we are able to determine the exciton ground state energy more accurately and to identify higher excited exciton states up to the 5S level. Data of the effective masses for the light hole and the heavy hole are given. Furthermore, the effect of nonparabolicity is discussed.

We analyze the Zeeman effect of the 4113/2 _ 4115/2 transition of Er3+ in GaAs:Er,O grown by metal-organic vapor-phase epitaxy. The photoluminescence spectrum has been assigned previously to one specific Er-O complex. The dominant optical transition at 1538 nm (6499.5 cm-'), which shows a full width at half maximum of only 0.05 cm-', has been investigated by high-resolution Zeeman spectroscopy. A highly anisotropic Zeeman pattern is found which indicates the low symmetry of the underlying complex. A detailed analysis shows that the defect has a predominant rhombic symmetry C 2 ,,. Additionally, smaller contributions of a crystal field with a monoclinic symmetry Clh are found. The results provide further arguments that an ErO 2 complex is the responsible center observed.

By photoluminescence and by Zeeman spectroscopy we study the characteristic 4f luminescence transition 3H5 → 3H6 at 1.0 eV of thulium in gallium arsenide which has been reported recently. It turns out that optically active Tm3+, which is present in mainly one specific type of center, does not occupy a simple substitutional lattice site. The results show a considerable tetragonal crystal field. The excitation mechanism of the 1.0-eV luminescence is investigated by photoluminescence excitation. The 3H5 → 3H6 is pumped most efficiently by trapping of free excitons.