To increase the optical output of a lighting system, high power Light Emitting Diodes are requested to operate at high currents; however, the maximum drive current is limited by the reliability of the devices. With this work we report on the effects of step stress carried out at increasing bias up to extreme current levels. By means of optical, electrical and photoluminescence analysis we hypothesize that the optical power decrease is related a degradation of the current transport layers of the devices and that an accurate control of the current crowding is crucial in extending the operating range of high power devices.

The aim of this paper is to give a thorough overview of flash memory cells. Basic operations and charge-injection mechanisms that are most commonly used in actual flash memory cells are reviewed to provide an understanding of the underlying physics and principles in order to appreciate the large number of device structures, processing technologies, and circuit designs presented in the literature. New cell structures and architectural solutions have been surveyed to highlight the evolution of the flash memory technology, oriented to both reducing cell size and upgrading product functions. The subject is of extreme interest: new concepts involving new materials, structures, principles, or applications are being continuously introduced. The worldwide semiconductor memory market seems ready to accept many new applications in fields that are not specific to traditional nonvolatile memories.