The distinct visible electroluminescence (EL) at room temperature has been realized based on n-ZnO∕p-Si heterojunction. The EL peak energy coincided well with the deep-level photoluminescence of ZnO, suggesting that the EL emission was originated from the radiative recombination via deep-level defects in n-ZnO layers. The transport mechanisms of the diodes have been discussed with the characteristics of current-voltage (I-V) and light-output–voltage (L-V), in terms of the energy band diagram of ZnO∕Si heterojunction. The tunneling mechanism via deep-level states was the main conduction process at low forward bias, while space-charge-limited current conduction dominated the carrier transport at higher bias. Light-output–current (L-I) characteristic of the diode followed a power law such as L∼Im, which showed a superlinear behavior at low injection current and became almost linear due to the saturation of nonradiative recombination centers at high current level.

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We report on the realization of ZnO homojunction light-emitting diodes (LEDs) fabricated by metalorganic chemical vapor deposition on (0001) ZnO bulk substrate. The p-type ZnO epilayer was formed by nitrogen incorporation using N2O gas as oxidizing and doping sources. Distinct electroluminescence (EL) emissions in the blue and yellow regions were observed at room temperature by the naked eye under forward bias. The EL peak energy coincided with the photoluminescence peak energy of the ZnO epilayer, suggesting that the EL emissions emerge from the ZnO epilayer. In addition, the current-voltage and light output-voltage characteristics of ZnO homojunction LEDs have also been studied.

The fundamental optical properties of Ga-doped ZnO films grown by metalorganic chemical vapor deposition were investigated by room-temperature transmittance and photoluminescence (PL) spectroscopy. The Burstein–Moss (BM) shift of the absorption edge energy is observed at the carrier concentration up to 2.47×1019cm−3. The absorption edges are fitted to a comprehensive model based on the electronic energy-band structure near critical points plus relevant discrete and continuum excitonic effects, taking account of the Fermi-level filling factor. The theoretical calculation for BM effect is in good agreement with the experimental facts, considering the nonparabolic nature of conduction-band and band-gap renormalization (BGR) effects. Meanwhile, the monotonic redshift of the near-band-gap emission detected by PL measurements has also been observed with increasing free-carrier concentration, which is attributed to the BGR effects, and can be fitted by an n1∕3 power law with a BGR coefficient of 1.3×10−5meVcm.

Phosphorus-induced lattice dynamic behaviors in ZnO:P epilayers grown by the metalorganic chemical vapor deposition technique have been studied using the Raman scattering method. Additional modes around 504, 520, 655, and 866cm−1 are attributed to the disorder-activated modes due to the breakdown of translational symmetry by P doping, well supported by the reported ab initio calculations of lattice dynamics in w-ZnO. Two modes around 364 and 478cm−1 are assigned to the local vibrational modes of Zn–P and P–O pairs, respectively. The correlation of transport and vibrational properties demonstrates the complex doping mechanism and the amphoteric nature of P dopant in ZnO. In addition, the redshift of 2 longitudinal optical multiphonon around 1154cm−1 is possibly originated from the variation of short-range forces in ZnO uniaxial lattice caused by P incorporation.

The carrier recombination processes in p-type ZnO epilayers with P monodoping and In–P codoping have been studied by temperature-dependent photoluminescence spectroscopy. Good correlations were observed between carrier recombination and acceptor and donor energy levels. The exciton transition feature of acceptor-bound excitons (3.350eV), the free electron-acceptor emission (3.315eV), and the donor-acceptor-pair emission (3.246eV) exhibited different carrier recombination associated various defect complexes. The origins of two broad emissions at ∼2.99 and ∼2.89eV were found to be due to different photoelectron radiative transitions associated with deep level acceptors (isolated Zn vacancies). The acceptor-bound energies for P monodoped and In–P codoped epilayers ∼195 and ∼127meV, respectively. The small binding energy is helpful for acceptor ionization at room temperature, resulting in a high hole concentration in the codoped epilayer.

To realize the hole-mediated ferromagnetism, manganese and nitrogen-codoped ZnO ͑Zn 1−x Mn x O:N͒ films were prepared on sapphire ͑0001͒ by reactive radio-frequency ͑rf͒ magnetron sputtering from Zn 0.97 Mn 0.03 O ceramic targets using N 2 gas. X-ray photon spectra reveal that the doped Mn ions are mainly in divalent states and the coexistence of O -Zn and N -Zn bonds in the films. According to the absorption spectra, the band gap of Zn 0.97 Mn 0.03 O : N films is about 3.15 eV, which is slightly lower than that of ZnO films ͑3.20 eV͒. Compared with Zn 0.97 Mn 0.03 O films, ferromagnetic behavior of Zn 0.97 Mn 0.03 O : N films were significantly changed with a coercivity of about 70 Oe, a saturation magnetization of 0.92 B /Mn 2+ and a remanance over 0.15 B /Mn 2+ at 300 K, while at 10 K, they increased to be about 110 Oe, 1.05 B /Mn 2+ and 0.23 B /Mn 2+ , respectively. However, rapid thermal annealing treatment in pure oxygen results in a significant decrease on the magnetic properties of the films.

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