We show that N-doped ZnO films grown on sapphire can exhibit significant (∼1018 cm−3) room-temperature p-type behavior when sufficient nitrogen (N) is incorporated and the material is annealed appropriately. Substitutional N on the oxygen (O) sublattice is a deep acceptor; however, shallow acceptor complexes involve N, H, and zinc vacancies (VZn). Combining secondary ion mass spectrometry, Raman-scattering, photoluminescence, and Hall-effect data, we establish the evolution of N from its initial incorporation on a Zn site to a final shallow acceptor complex VZn_NO_H+ with an ionization energy of ca. 130 meV. This complex is responsible for the observed p-type behavior.

The photoluminescence (PL) properties of ZnCdO alloy are investigated at various temperatures. Each PL profile contains four distinct peaks: P1, P2, P3, and P4. Peak P4 is due to free-excitonic recombination. The temperature mapping of the P3 peak position shows an S-shaped shift similar to the InGaN system due to the inhomogeneous distribution of Cd in ZnCdO alloy. The peak P2 is attributed to the phonon replica of the localized excitonic emission (P3). The linewidth of the photoluminescence profiles of the ZnCdO alloy is shown to depend on the concentration of Cd.

a b s t r a c tThe effect of Al doping concentration and oxygen ambient pressure on the structural and optical properties of chemical vapor deposition-grown, Al-doped ZnO nanowires is studied. As Al doping increases, the strength of the broad visible emission band decreases and the UV emission increases, but the growth rate depends on the oxygen pressure in a complex manner. Together, these behaviors suggest that Al doping is effective in reducing the number of oxygen vacancies responsible for visible emission, especially at low oxygen ambient pressure. The intensities and quantum efficiencies of these emission mechanisms are discussed in terms of the effect growth and doping conditions have on the underlying excitonic decay mechanisms.

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The role of hydrogen and methane dissociation process in induction plasma synthesis of graphene nano-flakes (GNF) is studied by the optical emission spectroscopy of Ar/H2/CH4 plasma. The condensation of C2 species formed due to methane decomposition produces GNF, which depends on pressure. Electron impact and dehydrogenation processes dissociate methane, which promotes and hinders the GNF production, respectively. The effect of hydrogen is insignificant on quality, size and morphology of the GNF. The CH4 flow rate has no influence on particle temperature but has effect on cooling rate at the point of nucleation and, therefore, on production rate and thickness of GNF.

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The ZnO nanowires are grown by thermal evaporation on pulsed laser deposited ZnO buffer layer on silicon. Photoluminescence of ZnO nanowires is studied at various temperatures in the range from 6 K to room temperature and varying excitation intensities. At 6 K, the photoluminescence profile of ZnO nanowires shows bound exciton, free excitons (FXAn=1,FXAn=2), longitudinal optical phonon replicas (FXAn=1-mLO, m=1, 2, 3) of free exciton (FXAn=1), and donor acceptor pairs. The first longitudinal optical phonon replica (FXAn=1-1LO) dominates at room temperature. Photoluminescence peak shifts by 47 meV from free exciton energy with the increase in temperature to room temperature.

Articles you may be interested inTemperature-dependent Hall and photoluminescence evidence for conduction-band edge shift induced by alloying ZnO with magnesium Appl. Phys. Lett. 95, 152105 (2009); 10.1063/1.3236771 High pressure photoluminescence of CdZnSe quantum dots: Alloying effectPhotoluminescence ͑PL͒ of ZnCdO alloy with medium Cd concentration ͑50 wt %͒ is studied at different temperatures and at varying excitation intensity. The PL peak position shows red-blue-red ͑S-shaped͒ shift with increase in temperature due to potential fluctuations on alloying. The line width of PL profile shows increasing-decreasing-increasing behavior with increase in temperature. The dependence of S-shape behavior on Cd concentration is analyzed.