Search

Low frequency noise of current and light intensity of ultraviolet light emitting diodes (LED) with wavelength from 265 to 340 nm are the superposition of the 1/f and generation-recombination noise. The dependence of generation-recombination noise on the LED current has a maximum caused by a relatively shallow trap level in the quantum well. The upper bound of this trap level concentration is estimated to be Nt=7×1015 cm-3. The relative spectral noise density of the light intensity fluctuations decreased with an increase of the LED forward current. At high currents, the difference in the noise level for LEDs with different wavelength is small and is of the same order of magnitude or even smaller than for visible LEDs. [ABSTRACT FROM AUTHOR]

Low-frequency fluctuations of current and light intensity were measured for different types of ultraviolet (UV) light-emitting diodes (LEDs) with wavelengths from 280 to 375 nm. These UV LEDs are suitable for studying steady-state and time-varying UV fluorescences of biological materials. The correlation coefficient between the current and light intensity fluctuations varies with the LED current and load resistance. This dependence is explained in terms of contributions to the 1/f noise from the active region and from the LED series resistance. The noise level could be reduced by operating the UV LEDs at a certain optimum current level and with large external series resistance. [ABSTRACT FROM AUTHOR]

Low frequency fluctuations in light intensity were measured from five different types of commercially available light emitting diodes with wavelengths from 375 nm to 740 nm and from two different halogen lamps. At low frequencies below 10-100 Hz some light emitting diodes (LEDs) can provide lower levels of noise than halogen lamps. A noise quality factor Β is proposed in order to characterize noise behavior of LEDs. [DOI: 10.1063/1. [ABSTRACT FROM AUTHOR]

1/f noise in AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors has been measured at 300 K in strong magnetic fields up to 10 T. The devices exhibited strong geometric magnetoresistance. The magnetic-field dependence of the 1/f noise shows that fluctuations of the number of electrons is the dominant mechanism of the 1/f noise. [ABSTRACT FROM AUTHOR]

Optimization of the migration-enhanced metalorganic chemical vapor deposition and further optimization of the contact and active layer design for 280 nm light-emitting diodes resulted in large improvement of cw and pulsed output power and in a superior spectrum purity. The ratio of the main peak to the background luminescence determined by the detection system is higher than 2000:1 at 20 mA dc. The on-wafer cw power was measured to be 255 μW at 20 mA dc. The power popped up exceeding 1 mW for a packaged device under 25 mA dc and 9 mW under pulse 200 mA. The maximum wall-plug-efficiency of 0.67% was obtained for the packaged device at 25 mA dc. [ABSTRACT FROM AUTHOR]

The UV-LED controlled phase shifter of an RF signal based on a GaN-sapphire surface-acoustic-wave (SAW) filter has been implemented. At the optical wavelength 298 nm and SAW frequency 307 MHz, the UV-induced relative change in SAW velocity per unit optical power density is 2×10-6 (µW/mm2)-1 corresponding to 3.7° phase shift. The phase modulation of an RF signal by rectangular UV pulses has been demonstrated. The efficiency of the phase shifter can be considerably improved by proper selection of sheet-resistivity of the GaN layer. [ABSTRACT FROM AUTHOR]