Engineering topics

Yakimov, E B

Publications and source records attributed to Yakimov, E B.

3 records

DOE OSTI2011

X-ray beam induced current method at the laboratory x-ray source

The x-ray beam induced current method (XBIC) is realized on the laboratory x-ray source using the polycapillary x-ray optics. It is shown that rather good images of grain boundaries in Si can be obtained by this method. The parameters of x-ray beam are estimated by the simulation of Schottky diode image. A good correlation between the experimental and calculated grain boundary XBIC contrast is obtained. The possibilities of laboratory source based XBIC method are estimated.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2011

Neutron doping effects in epitaxially laterally overgrown n-GaN

Thermal neutron irradiation and annealing effects were studied for undoped n-GaN prepared by epitaxial lateral overgrowth (ELOG). Electron beam induced current (EBIC) imaging and profiling prior to irradiation showed that the residual donor doping in our ELOG samples was about three times higher in the high-dislocation-density ELOG wing than in the low-dislocation-density ELOG window regions. Irradiation with thermal neutrons and subsequent annealing led to greatly improved doping uniformity, as evidenced by EBIC imaging. The neutron transmutation doping avoids the anisotropy of donor incorporation efficiency for different planes during ELOG and provides a uniform doping environment. Capacitance-voltage profiling on such samples showed the presence of electrically active centers with concentration close to the concentration of Ge donors produced by Ga interaction with thermal neutrons.

36 MATERIALS SCIENCE↗

DOE OSTI2011

Effect of the silicon doping level and features of nanostructural arrangement on decrease in external quantum efficiency in InGaN/GaN light-emitting diodes with increasing current

A comprehensive study of blue light-emitting diodes based on quantum-well InGaN/GaN structures with external quantum efficiencies {eta} of up to 40% has been carried out. It is shown that, in the general case, the manner in which the efficiency depends on the current density j is determined by the competition of contributions to the radiative recombination of localized and delocalized carriers. The contribution of the latter grows with worsening structural organization of the nanomaterial, increasing temperature and drive current, and decreasing width of the depleted layer in the active region (under zero bias). The steepest efficiency droop relative to the maximum value (by up to a factor of 2 at j Almost-Equal-To 50 A cm{sup -2}) is observed in the case of heavy doping of the n{sup +}-region (to 10{sup 19} cm{sup -3}) and upon appearance of compensated layers in the active or p{sup +}-region. At j > 50 A cm{sup -2}, the contribution of delocalized carriers is predominant and the current dependences of efficiency are of uniform type, approximated with {eta}(j) {proportional_to} j{sup -b}, where 0.2 < b < 0.3.

36 MATERIALS SCIENCE↗