Shmidt, N M | Search NASA

DOE OSTI2012

Low-frequency noise in as-fabricated and degraded blue InGaAs/GaN LEDs

Study of the spectral noise density and its dependence on current density in as-fabricated and degraded blue light-emitting diodes (LEDs) based on InGaN/GaN quantum-well structures are reported. It is shown that defects are generated nonuniformly in the course of degradation, being concentrated along extended defects penetrating into the active region of LEDs. It is demonstrated that the decrease in the external quantum efficiency in the course of aging is due to the enhancement of charge transport uniformity, which leads to the formation of shunts and local overheating regions. Typically, in blue LEDs, these effects are responsible for the ambiguous development of the degradation process, which hinders prognostication of LED service life. The effect of noise suppression is observed in a narrow current density range (10{sup -2} to 10{sup -1} A cm{sup -2}) corresponding to the onset of radiative recombination.

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↗