摘要:

We report on a semiconductor superlattice oscillator for generation of millimeter waves (frequency 65 GHz). The main element of the oscillator is a doped short-period GaAs/AlAs superlattice with negative differential conductance. The oscillator is due to current oscillations caused by charge density domains. The oscillator delivered, at an efficiency of 0.2&percent; for the conversion of electrical power to radiation power, a power of 100 &mgr;W in a bandwidth of the order of 200 kHz. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121038

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Cathodoluminescence measurements were performed for carbon doped and undoped aluminum nitride thin films in the temperature range from liquid helium to room temperature. The AlN films were grown on three different substrates: 6H–SiC, 4H–SiC, and sapphire. From these samples, a strong luminescence peak surrounded by two weaker peaks in the near band-edge region, near 6 eV, was observed. For AlN on sapphire, this near band-edge transition can be further resolved into three peaks at 6.11, 5.92, and 5.82 eV. These peaks are believed to be due to exciton recombination. The effects of substrate materials and carbon doping on the exciton peak were discussed. The temperature dependence of the peak position and line width of this transition was also studied. The temperature coefficient of the band-gap energy is estimated to be 0.51 meV/K. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121039

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The interband optical transitions in single-crystal GaN films grown by metal organic chemical vapor deposition have been studied at 10 K and room temperature using nondegenerate nanosecond optical pump-probe techniques. At low temperatures, strong, well-resolved features are seen in the absorption and reflection spectra corresponding to the1sA and B exciton transitions. These features broaden and decrease in intensity due to the presence of a high density of photoexcited free carriers and are completely absent in the absorption and reflection spectra as the excitation density,Iexc,approaches3 MW/cm2,resulting in induced transparency in transmission measurements. The absorption spectra also show induced absorption below the band gap asIexcis increased. Both the observed induced transparency and induced absorption were found to be extremely large, exceeding4×104 cm−1as the pump density approaches3 MW/cm2at 10 K. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121040

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have achieved the highest barrier height (0.90 eV) with a Schottky contact scheme of W-B-N/GaAs after rapid thermal annealing (RTA) at 700 °C, and even after the RTA at 900 °C, its barrier height (0.77 eV) is relatively higher than those of W (0.55 eV) and W-N/GaAs Schottky contacts (0.68 eV). Deep level transient spectroscopy and carrier density profile measurements show that the higher barrier height and lower leakage current of the W-B-N/GaAs diode are due to the W-B-N film that suppresses changes of the surface carrier and EL2 trap concentrations after the RTA. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121041

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The growth of nanocrystalline silicon on an aluminum underlayer of 4–32 nm thickness on silica substrates by plasma-enhanced chemical vapor deposition (PECVD) or sputter deposition is observed at standard conditions for the preparation of device quality hydrogenated amorphous silicon (substrate temperature of 500 K, deposition rate of 0.5 &mgr;m/h). The crystallite size determined by wide angle x-ray scattering ranges from 10 to 30 nm, and the crystallite fraction reaches 25&percent;. The efficiency of aluminum mediated crystallization is about one order of magnitude higher for PECVD films than for sputtered films. Variations of the incident angle of the x rays show that the formation of silicon crystallites takes place at the Al/Si interface. Diffusion of Al into the silicon is enhanced for the PECVD films, whereas it plays a comparatively minor role for sputter deposition. The effect of the aluminum mediated crystallite growth is related to the existence of a metastable aluminum silicide and diffusion processes. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121042

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We measured the static error rate of a high-Tcsuperconductor dc superconducting quantum interference device (SQUID), which, in the form as a storage loop for single flux quanta, is a basic element of rapid single flux quantum circuits. Using high-Tcmultilayer bicrystal technology, we fabricated a stacked dc SQUID pair, one SQUID serving as the storage loop, the other one as the readout device. The escape rate of a stored flux quantum was measured as a function of the bias current at a temperature of 28 K. The measured error rates were in good agreement with a model calculation based on thermally activated barrier crossing. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121043

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A systematic study of the intermediate frequency noise bandwidth of Nb thin-film superconducting hot-electron bolometers is presented. We have measured the spectrum of the output noise as well as the conversion efficiency over a very broad intermediate frequency range (from 0.1 to 7.5 GHz) for devices varying in length from 0.08 &mgr;m to 3 &mgr;m. Local oscillator and rf signals from 8 to 40 GHz were used. For a device of a given length, the spectrum of the output noise and the conversion efficiency behave similarly for intermediate frequencies less than the gain bandwidth, in accordance with a simple thermal model for both the mixing and thermal fluctuation noise. For higher intermediate frequencies the conversion efficiency decreases; in contrast, the noise decreases but has a second contribution which dominates at higher frequency. The noise bandwidth is larger than the gain bandwidth, and the mixer noise is low, between 120 and 530 K (double side band). ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121044

出版商:AIP    

年代:1998

数据来源: AIP