K. Yang

Precipitation of Cu and Fe in Dislocated Floating-Zone-Grown Silicon

Precipitation behaviors of Cu and Fe in dislocated Floating-zone-grown silicon crystals are investigated by means of transmission electron microscopy (TEM) and the electron-beam-induced-current (EBIC) technique. Cu precipitation on dislocations is affected significantly by the cooling rate of a specimen after contamination. Cu develops precipitate colonies at some special sites on dislocations and does not decorate other parts of dislocations if the specimen is cooled slowly. These preferential precipitation sites are suggested to be non-dissociated edge-type dislocation segments. The fast cooling of a specimen leads to that Cu precipitates on all of dislocations. Fe decorates all of dislocations uniformly, irrespective of the cooling rate of a specimen.

Gettering of Fe impurities by bulk stacking faults in Czochralski-grown silicon

Gettering of Fe impurities by bulk stacking faults in Czochralski-grown silicon are investigated by means of the electron-beam-induced-current technique and transmission electron microscopy. It is found that Fe impurities only precipitate on Frank partial dislocations bounding stacking faults when the specimen is cooled slowly; however, both Frank partials and fault planes are decorated by Fe impurities when the specimen is cooled rapidly. It is explained that small oxygen precipitates on fault planes serve as the gettering centers for Fe impurities in the fast cooled specimen.

Study of Photocurrent Properties of GaN Ultraviolet Photoconductor Grown on 6H-SiC Substrate

The properties of a photoconductive ultraviolet detector based on a GaN epilayer grown on a 6H-SiC substrate using metal-organic chemical vapor deposition were investigated. We obtained the detectable energy span of the device up to the ultraviolet region by photocurrent measurement. The spectral responsivity remained nearly constant for wavelengths ranging from 250 to 365 nm and dropped by three orders of magnitude within 15 nm of the band edge from 365 nm to 380 nm.The detector was measured to have a responsivity of 133 A/W at a wavelength of 360 nm under a 5 V bias, and the voltage-dependent responsivity was evatuated. Furthermore, a convenient method to determine the response time was developed. The relationship between response time and bias was obtained.

High-Quality Photoconductive Ultraviolet GaN/6H-SiC Detector and Its Properties

The properties of photoconductive ultraviolet detector based on GaN epilayer grown on 6H-SiC substrate by metalorganic chemical vapor deposition were investigated in this paper. We obtained the detectable energy span of the device up to ultraviolet by photocurrent measurement. The spectral responsivity remained nearly constant for wavelengths from 250 to 365 nm and dropped by three orders of magnitude within 10 nm of the band edge (by 380 nm). The detector was measured to have a responsivity of 133 A/W at a wavelength of 360 nm under a 5-V bias, and the voltage-dependent responsivity was performed. Furthermore, an easy method was developed to determine the response time, and the relationship between response time and bias was obtained.

Optical Characterization of GaN Films Grown on (0001) Sapphire Substrate

The optical properties of single crystal hexagonal GaN films grown on (0001) sapphire substrate by metalorganic chemical vapor deposition were investigated. The energy gap of hexagonal GaN was determined as 3.39 and 3.400 eV by optical transmission and photoreflectance, respectively. The refractive index of GaN as a function of photon energy was drawn from the transmission spectrum. Furthermore, Raman scattering spectra were employed to study the phonon modes of the GaN film. The properties of LO phononplasmon coupled modes were further studied, and the carrier concentration and damping constant were determined by line-shape fitting of the coupled modes.

Electrical and Optical Properties of InGaN/AlGaN Double Heterostructure Blue Light-Emitting Diodes

In this paper, we studied the electrical and optical characteristics of Nichia double heterostructure blue light-emitting diodes, with In 0.06 Ga 0.94 N:Zn, Si active layer, at 77 and 300 K. Measurement of the forward bias current-voltage behavior of the device demonstrates a departure from the Shockley model of p-n diodes, and it is observed that the dominant mechanism of carrier transport across the junction is associated with carrier tunneling. Electroluminescence experiments of the devices were performed. We obtained an emission peak located at 2.80 eV, and a relatively weaker short-wavelength peak of 3.2 eV. A significant blue shifts of the optical emission peak which is consistent with the tunneling character of electrical characteristics was observed. Furthermore, we studied the properties of electroluminescence under various pulsed currents, and a degradation in I-V characteristics and a low resistance ohmic short were observed.