We study the influence of nitrogen, a potential acceptor in ZnO, on the lattice dynamics of ZnO. A series of samples grown by chemical vapor deposition ͑CVD͒ containing different nitrogen concentrations, as determined by secondary ion mass spectroscopy ͑SIMS͒, was investigated. The Raman spectra revealed vibrational modes at 275, 510, 582, 643, and 856 cm Ϫ1 in addition to the host phonons of ZnO. The intensity of these additional modes correlates linearly with the nitrogen concentration and can be used as a quantitative measure of nitrogen in ZnO. These modes are interpreted as local vibrational modes. Furthermore, SIMS showed a correlation between the concentration of incorporated nitrogen and unintentional hydrogen, similar to the incorporation of the p-dopant magnesium and hydrogen in GaN during metalorganic CVD.There is increasing interest in investigating the properties of ZnO epitaxial films with a direct gap of 3.37 eV at room temperature. 1 The material is a potential competitor for GaN-based light-emitting devices in the ultraviolet and blue spectral range. There are reports of superior ZnO properties such as a high exciton binding energy combined with a low lasing threshold density 2 and a good resistance to bombardment with high-energy particles. 3,4 For other wide-band-gap semiconductors as GaN ͑Ref. 5͒ and ZnSe ͑Ref. 6͒ controlled p-type doping is problematic. As-grown ZnO typically has n-type conductivity with background concentrations between 10 16 and 10 17 cm Ϫ3 . However, there have been reports on the synthesis of p-conducting ZnO doped with As ͑Ref. 7͒ and a Ga/N codoping 8 as well as the fabrication of a p-n-junction by excimer-laser doping. 9 In this letter, we report on doping experiments with nitrogen as a potential acceptor and its influence on the lattice dynamics of ZnO.The ZnO thin films under investigation were grown by chemical vapor deposition ͑CVD͒ using a home built epitaxy system which consists of a horizontal quartz reactor and a resistance heating with different temperature zones. Metallic zinc was kept in one zone at a temperature of 470°C the growth temperature was 650°C. We used NO 2 as oxygen precursor and NH 3 as nitrogen source for the doping experiments. The epitaxial films were deposited on GaN/sapphire templates which offers the advantage of a lattice parameter similar to ZnO. We investigated samples containing different nitrogen concentrations. Secondary ion mass spectroscopy ͑SIMS͒ was applied to determine the concentration of nitrogen and unintentional dopants such as hydrogen. The primary ion species was cesium. Nitrogen was detected as 14 N 16 O Ϫ and hydrogen as 64 Zn 1 H Ϫ clusters. The given abso-lute concentrations are accurate to within half an order of magnitude. Despite this accuracy the relative error is less than 10%. The Raman-scattering experiments were carried out in backscattering geometry with a triple-grating spectrometer equipped with a cooled charge-coupled device detector. The lines at 488 and 514.5 nm of an Ar ϩ /Kr ϩ mixedgas laser were used...

Recombination processes in Ga1−xInxNyAs1−y/GaAs multiple quantum wells (MQWs) were investigated as function of the nitrogen molar fraction. We found a pronounced S-shaped behavior for the temperature-dependent shift of the photoluminescence emission similar to the ternary nitrides InGaN and AlGaN. This is explained by exciton localization at potential fluctuations. Time-resolved measurements at 4 K reveal an increase of the decay time with decreasing emission energy. A model based on lateral transfer processes to lower-energy states is proposed to explain this energy dependence. The formation of tail states in the Ga1−xInxNyAs1−y/GaAs MQWs is attributed to nitrogen fluctuations.

Local vibrational modes in the region of the acoustic and optical phonons are reported for Mg-doped GaN grown by molecular beam epitaxy. The modes, studied by Raman spectroscopy, appear in addition to the known modes in the high-energy region around 2200 cm Ϫ1. We suggest disorder-activated scattering and scattering from Mg-related lattice vibrations to be the origin of the low-energy modes. Our assignment is supported by calculations based on a modified valence-force model of Kane. Temperature-dependent measurements between 4 and 300 K exclude an electronic Raman-scattering mechanism. We also report a new line at 2129 cm Ϫ1 and discuss the origin of all five observed high-energy modes.

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The compensation of Mg-doped GaN is systematically studied by low-temperature photoluminescence and Raman spectroscopy using a series of samples with different Mg concentrations. Strongly doped samples are found to be highly compensated in electrical measurements. The compensation mechanism is directly related to the incorporation of Mg. Three different deep donor levels are found at 240±30, 350±30, and 850±30 meV from the conduction band, each giving rise to deep unstructured donor-acceptor pair emission.