A single crystal GaN thin film was successfully grown on a Si (111) substrate by means of atmospheric pressure metalorganic chemical vapor deposition. Though there is a large difference in thermal expansion coefficients between GaN and Si, an intermediate layer consisting of AlN and AlGaN improved the quality of GaN on Si and reduced meltback etching during growth. Pits and cracks were not observed on the substrate and a mirror-like surface was obtained. The full-width at half maximum (FWHM) of the double-crystal X-ray rocking curve for GaN(0004) was 600 arcsec. Photoluminescence measurement at room temperature for a Si-doped film revealed a sharp band-edge emission with a FWHM of 62.5 meV, which is the narrowest value reported to date.

Zinc oxide is a wide bandgap semiconductor with potential applications in optoelectronic devices. The greatest challenge for these applications, however, remains the fabrication of reliable and stable p-type ZnO thin films. Here we report stable phosphorus-doped p-type ZnO thin films grown on (0001) sapphire substrates by pulsed laser ablation. While as-deposited films all show n-type conductivity, films grown at 600°C become p-type after annealing in oxygen atmosphere with a resistivity of 4.9 × 10 1 X cm, a Hall mobility of 1 cm 2 V -1 s -1 , and a hole concentration of 1.3 × 10 17 cm -3 . Such p-type films have been stable under ambient conditions for 16 months so far without apparent degradation. Transmission electron microscopy reveals that the p-type films consist of a high density of dislocations, which enhance both the solubility of phosphorus and the formation of Zn vacancies to facilitate the n-to-p conversion of electrical conductivity. These studies provide microscopic evidence of the amphoteric nature of the phosphorus dopant in ZnO. There has recently been an increasing interest in ZnO for applications in optoelectronics such as light emitting diodes, ultraviolet (UV) lasers, and UV light detectors because of its wide bandgap (3.37 eV). In comparison with GaN, ZnO has some obvious advantages for optoelectronic applications due to the availability of single crystal substrates, relatively low growth temperatures (T G ), and a large exciton binding energy (∼ 60 meV).[1] Optically pumped excitonic lasing of ZnO thin films at room temperature (RT) has been reported. [2,3] Lasing effects in ZnO nanowire arrays have been demonstrated, [4] and electroluminescence (EL) has been observed at room temperature in thin-film ZnO homojunctions. [5][6][7] Although p-type ZnO thin films were reported by several groups, they showed high resistivity and/or poor stability and reproducibility. Thus, the greatest remaining challenge for ZnO optoelectronics is the reproducible fabrication of stable p-type ZnO thin films. Like many other II-VI semiconductors, ZnO has asymmetric doping limits: [8] it can be easily doped n-type, [9] but remains strongly resistant to p-type doping.[10] Though nitrogen is theoretically the most promising acceptor for ZnO, its low solubility and compensation by donors such as hydrogen [11] and Zn interstitials [12] are major obstacles.As alternatives to N, larger-size group V elements such as P, As, Sb and Bi have been widely studied. Puzzling observations of p-type conductivity in such materials have stimulated theoretical investigations into the electronic structure of the defects induced by P, As or Sb in ZnO. Limpijumnong et al. [13] predicted that under oxygen-rich growth conditions, a complex involving a group V antisite and two zinc vacancies (V Zn ) would have a low formation energy, and behave as a shallow acceptor with an ionization energy of 150-160 meV. Lee et al. used the same concept to study phosphorus complexes in ZnO.[14] One of the most important conclusions from these studies ...

The electrical characteristics of Ag, Ti, Au, Pd and Ni Schottky contacts on GaN and Al0.11Ga0.89N grown by metalorganic chemical vapour deposition (MOCVD) on sapphire substrates have been investigated. Al0.11Ga0.89N Schottky barrier height values are bit higher than the values of GaN contacts except Ti Schottky contacts. Fermi-level pinning has been observed for both GaN and Al0.11Ga0.89N Schottky contacts. The pinning degree of GaN and Al0.11Ga0.89N are much less than GaAs, Si and GaP, but both of them may be similar to CdS.

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The normal-incidence reflectance measurement was employed to obtain the free exciton transition energy (E FX) of AlGaN alloys in Al x Ga 1Ϫx N/GaN/sapphire heterostructure grown by metalorganic chemical vapor deposition. It was found that the thickness variation of the AlGaN layer may cause a noticeable change in the line shape of reflectance spectrum and impede the identification of the desired excitonic position. By using a reflection model of two absorbing layers with a transparent substrate, the experimental reflectance spectra were theoretically simulated and utilized to explain the reflection mechanism in Al x Ga 1Ϫx N/GaN heterostructures. On the basis of the above analysis, the feasibility of the reflectance measurement for such heterostructures is confirmed. At room temperature, the E FX s obtained from the fitting showed an excellent agreement with the corresponding peak energies in the photoluminescence spectra. Furthermore, at the optical energy position about 100 meV above the E FX , the spectral feature of exciton-LO phonon interaction was observed in the reflectance spectrum record for low Al composition (xр0.16). Using the Al mole fraction derived from x-ray diffraction measurement, the bowing parameter of the epitaxial AlGaN layer was determined. In the range of 0рxϽ0.3, the resulting bowing parameter shows a downward value of 0.53 eV.