Index of content:
Volume 87, Issue 10, 15 May 2000
87(2000); http://dx.doi.org/10.1063/1.373025View Description Hide Description
By using a correlation spectrum analyzer, we succeeded in performing direct measurements of the current noise spectra of cadmium telluride (CdTe)diodes, commonly used in γ-ray spectrometers. The current noise spectra have been measured over a wide range of frequencies, from below 1 Hz up to 100 kHz, and for diode operating points from 0 up to 150 V. The device showed linear characteristics in all the bias range with a dynamic resistance of about 2 GΩ. Around the equilibrium condition (0–0.5 V), the white component of the noise spectrum is in agreement with the Johnson noise associated to the device resistance. As the bias is increased up to 150 V, the white noise level is shown to slowly approach the shot noise behavior. The white noise shows a cut-off frequency consistent with the carriers transit time across the device. In all the nonequilibrium conditions, the noise spectra also show a significant component whose power density increases with the square of the device current.
87(2000); http://dx.doi.org/10.1063/1.373026View Description Hide Description
We present a concept for a hot-electron direct detector capable of counting single millimeter-wave photons. The detector is based on a microbridge (1 μm size) transition edge sensor made from a disordered superconducting film. The electron–phonon coupling strength at temperatures of 100–300 mK is proportional to the elastic electron mean free path l and can be reduced by over an order of magnitude by decreasing l. The microbridge contacts are made from a different superconductor with higher critical temperatureNb, which blocks the thermal diffusion of hot carriers into the contacts. The low electron–phonon heat conductance and the high thermal resistance of the contacts determine the noise equivalent power of at 100 mK, which is times better than that of state-of-the-art bolometers. Due to the effect of disorder, the electron cooling time is at 0.1 K. By exploiting negative electrothermal feedback, the detector time constant can be made as short as without sacrificing sensitivity.
87(2000); http://dx.doi.org/10.1063/1.373027View Description Hide Description
Infrared emission at 1.54 μm excited optically and electrically from an erbium organic compound tris(acetylacetonato)(1,10-phenanthroline) erbium is observed. The rare-earth complex is dispersed into a polymer matrix of poly(N-vinylcarbazole) (PVK) to fabricate an electroluminescent (EL) device with an structure, where ITO represents indium–tin–oxide-coated glass. The device shows infrared EL emission at 1.54 μm, which suggests a simple and cheap method to obtain a light source for 1.54-μm-wavelength devices in optical communications.
Study of concentration-dependent Be diffusion in GaInP layers grown by gas source molecular beam epitaxy87(2000); http://dx.doi.org/10.1063/1.373028View Description Hide Description
Concentration-dependent Be diffusion in GaInP layers grown by gas sourcemolecular beam epitaxy has been studied using secondary ion mass spectrometry. At a growth temperature of 500 °C, apparent Be diffusion occurs at a doping level over At lower temperature, the Be profile exhibits a significantly reduced diffusion. In contrast to Zndiffusion in metalorganic vapor phase epitaxy, no enhancement of Be redistribution in GaInP by adjacent n-type layers occurs. These results are explained based on the interstitial–substitutional diffusion model. A GaInP tunnel diode with a high reverse-biased conductance of 15 mA/cm2 at 1.7 mV has been achieved.
87(2000); http://dx.doi.org/10.1063/1.373428View Description Hide Description
Photoluminescence was observed from pure perovskitelanthanum aluminate single crystalsgrown with a floating-zone method in reduced atmosphere. Emission was composed of a fast ultraviolet (UV) component and a broad visible emission with a lifetime of 13 μs. From the lifetime measurement, absorption spectra, excitation spectrum, and comparison between samples as-grown and annealed in oxygen, we assigned the UV emission to band-to-band emission or emission from polaron pairs. The visible component was assigned to emission from the excited state formed at oxygen defect sites. These emissions demonstrate the possibility of light-emitting devices made of perovskite oxides.