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The low frequency current and light intensity noise of the next generation light emitting diodes (LEDs) with wavelengths ranging from 265 to 340 nm is reported. The relative spectral noise density of the light intensity fluctuations decreased with an increase of the LED forward current and 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.

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]

The study of the electrical and noise properties of the AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs) at T=300 K in magnetic fields up to 10 T, where the devices exhibited a strong geometric magnetoresistance is presented. It was found that the magnetic field dependence of the 1/f noise is consistent with the conclusion that the fluctuation of the number of electrons is the dominant mechanism of the 1/f noise in these devices.

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]

Abstract: We demonstrate that high power light-emitting diodes (LED’s) exhibit low-frequency noise characteristics that are clearly superior to those of quartz tungsten halogen lamps, the non-coherent light source most commonly employed when freedom from intensity variation is critical. Their extreme stability over tens of seconds (combined with readily selectable wavelength) makes high power LED’s ideal light sources for DC recording of optical changes, from living cells and tissues, that last more than a few hundred milliseconds. These optical signals (ΔI/I0) may be intrinsic (light scattering, absorbance or fluorescence) or extrinsic (absorbance or fluorescence from probe molecules) and we show that changes as small as ~8 × 10-5 can be recorded without signal averaging when LED’s are used as monochromatic light sources. Here, rapid and slow changes in the intrinsic optical properties of mammalian peptidergic nerve terminals are used to illustrate the advantages of high power LED’s compared to filament bulbs. [Copyright &y& Elsevier]