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Carbon was in situ doped into GaN during halide vapor phase epitaxy and photoluminescence properties of the C-doped GaN film were investigated. It has been found that incorporation of carbon into GaN produces a significant yellow luminescence around 2.2 eV. The peak position of the yellow band blueshifts linearly and the intensity of that band monotonically decreases with measurement temperature, with systematic changes in the linewidth. These results suggest that multiple donor-acceptor recombination channels are involved in the yellow luminescence. © 1998 American Institute of Physics. ͓S0003-6951͑98͒02013-0͔Recent advances in GaN-based materials, 1 such as lightemitting diodes ͑LEDs͒, 2 have stimulated worldwide interest in developing novel GaN-based optoelectronic and electronic devices. Although a GaN continuous-wave ͑cw͒ injection laser diode has successfully been operated at room temperature with a lifetime greater than 1000 h, 3 some persistent problems in GaN material have to be resolved in order to realize higher performance devices. One such problem is the behavior and impact of carbon impurities in GaN. Carbon is one of the most common contaminants in the metalorganic vapor phase epitaxy ͑MOVPE͒ of GaN. 4 Carbon impurities in GaN are thought to occupy anion sites and act as acceptors. 5,6 Carbon may also combine with other defects, such as Ga vacancies, 7 due to the electronegativity and size differences between the carbon impurity and host atom. Carbon impurities are also believed to be related to yellow luminescence ͑YL͒ in GaN.7-10 Some of the initial photoluminescence ͑PL͒ studies on C-doped GaN were carried out by Pankove and Hutchby.7 They reported that C-implanted GaN exhibited a strong yellow luminescence band centered around 2.17 eV at 78 K. This band was attributed to defects arising from implantation damage, since the YL band could also be seen in samples implanted with other elements.7 Ogino and Aoki 8 found that the YL in both GaN microcrystal powder and needlelike crystals was greatly enhanced by intentional introduction of carbon into those materials. They concluded that the carbon impurities were crucial for YL. The YL was suggested to involve a radiative transition between a shallow donor, with the ionization energy of ϳ25 meV, and a deep acceptor, situated 860 meV above the top of the valence band. 8 Polyakov et al. 9 and Niebuhr et al. 10 have also attributed the observed YL in GaN grown by MOVPE to carbon impurities. The halide vapor phase epitaxy ͑HVPE͒ technique does not use carbon containing source materials but only uses NH 3 , HCl, and ultrapure Ga to synthesize GaN. 11,12 Carbon would only appear in these materials as an unintentional dopant. The YL band in typical HVPE-grown GaN is either absent or very weak 11,12 in agreement with the lack of carbon in the growth system. HVPE-grown GaN is therefore a suitable technique to study the correlation between YL and C atoms in GaN by intentional C doping during GaN growth. In this letter, we will report on the PL properties ...

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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 dominant oscillation shown in the laser-excited photoluminescence spectrum of the porous alumina film can be ascribed to the interference within a Fabry-Pérot optical cavity where the separation between two neighboring oscillations is highly sensitive to the film’s thickness and refractive index. The method, designated as photoluminescence oscillation, endows photoluminescence spectrum with another dimension and results in a nondestructive method for the measurement of the thickness and refractive index with a high resolution.

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GaN metal–semiconductor–metal photoconductive detectors have been fabricated on Si(111) substrates. The GaN epitaxial layers were grown on Si substrates by means of metalorganic chemical-vapor deposition. These detectors exhibited a sharp cutoff at the wavelength of 363 nm and a high responsivity at a wavelength from 360 to 250 nm. A maximum responsivity of 6.9 A/W was achieved at 357 nm with a 5 V bias. The relationship between the responsivity and the bias voltage was measured. The responsivity saturated when the bias voltage reached 5 V. The response time of 4.8 ms was determined by the measurements of photocurrent versus modulation frequency.

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