摘要:

This theoretical and experimental study was motivated by a specific need for a solid‐state microwave generator with an output efficiency exceeding 20% and focused on the properties of GaAs avalanche transit‐time devices. First, the dependence of the ionization rates and drift carrier velocities as a function of electric field and temperature is established. Then several methods of calculation, exact enough to take into account all the important efficiency‐limiting effects in the device, are discussed and used to derive theoretical figures for the efficiency of a GaAs IMPATT oscillator, special attention being given to the influence of the doping profile. Finally, the experimental study is described, including device realization and experimentally measured efficiencies, and a comparison between these and the calculated values is done. It is shown that the best calculated performances can reach 30% efficiency and that it is possible to obtain experimentally cw oscillation efficiencies exceeding 20% with GaAs IMPATT devices having special types of doping profile.

ISSN:0021-8979    

DOI:10.1063/1.1661879

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Photoconductive gains greater than unity can be obtained by illuminating a homogeneous photoconductor having blocking contacts with band gap radiation. A model is presented, which conceives such a possibility. Au contacts to CdSe form a Schottky barrier at the interface. Upon illumination the photogenerated holes are trapped in the Schottky barrier, shrinking the barrier and allowing injection of electrons in the CdSe. This gives rise to the possibility of gain greater than unity. Experimental evidence supporting the model is presented. Photoconductive gains as large as 300 have been measured when these films were illuminated with a photon flux of 2×1015photons/cm2/sec.

ISSN:0021-8979    

DOI:10.1063/1.1661881

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The effects of implanting silver, phosphorus, and cadmium ions in silver bromide microcrystals were ascertained using the intrinsic photosensitivity of these devices. Defects caused by implantation controlled the photocarrier trapping. After removal of these defects by annealing, both cadmium and phosphorus were the controlling species and increased the internal photosensitivity of the microcrystals.

ISSN:0021-8979    

DOI:10.1063/1.1661882

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Dynamic temperature configuration and current filamentation in single‐crystal silicon films on sapphire substrates were studied with high‐amplitude constant‐current pulse excitation using Sunshine's stroboscopic technique. Temperature configurations vary greatly depending upon the pulse duration and amplitude, electrode geometry magnitude of heat flow into the substrate, and magnitude of transverse heat flow. Filamentation occurs in two steps, each accompanied by a voltage drop. An initial broad filament forms as local regions rise in temperature beyond the peak of the resistivity‐temperature curve of the silicon. The second filamentation is a narrow melt channel that forms interior to the initial filament. A time‐dependent computer simulation is presented that includes both the heat flow into the substrate and transverse heat conduction. The model shows that a stable‐current filament can exist without a melt transition, but only for a very restricted range of current levels.

ISSN:0021-8979    

DOI:10.1063/1.1661883

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Chalcogenide amorphous threshold switching devices have been pulse switched and studied in the on‐regime by applying cw functions. A 1‐MHz square, sine, or triangular test wave of maximum amplitude ±7 V applied to a device which is then pulse switched (65, 30, or 10 V threshold), will cause the device to remain in the on‐regime after the set pulse turns off. Lowering the cw frequency or lowering the wave amplitude beneath critical values causes the specimen to turn off. At frequencies significantly above the turn‐off value, the positive and negative high‐current segments of theV‐Ion‐regime curve are connected by a very high‐resistance essentially linear region passing through zero. The on‐regime can be preserved in this manner at ambient temperatures varying from at least −196 to + 150 °C; however, increasing ambient temperature causes a decrease in the turn‐off frequency. Decreasing the wave amplitude causes an increase in the turn‐off frequency.

ISSN:0021-8979    

DOI:10.1063/1.1661884

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A 110‐mm‐square aperture face pumped Nd‐glass amplifier has been designed and tested under input beam energy density conditions of up to 5 J/cm2. The measured gain of 120‐psec pulses compares favorably with the calculated values based on a three‐level model of the amplifying medium. Maximum storage efficiency of 2.3%, high repetition rate of ½ pulse/min, and minimum beam distortion combine to make this design attractive for high‐peak‐power applications.

ISSN:0021-8979    

DOI:10.1063/1.1661885

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The reactions of silicon with Ni {001}, Ni {110}, and Ni {111} surfaces have been studied by means of low‐energy electron diffraction. On all three surfaces, at room temperature the silicon atoms are distributed at random and resulting films are amorphous. At temperatures of the order of 300∼400 °C ordered structures are formed: ac(2×1) structure on Ni {001} and ac(8×2) structure on Ni {110}. On Ni {111}, the√3structure that was predicted in a preceding paper is found to occur, but increasing silicon concentration on the surface leads to a 2×2 and then a 2×12 structure, defined in the text, the latter displaying only twofold symmetry. In all cases, the surface concentration of silicon is reduced, at higher temperatures, by the rapid diffusion of the silicon atoms into bulk nickel.

ISSN:0021-8979    

DOI:10.1063/1.1661886

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Transport properties ofn‐type germanium at 20 K have been calculated in the donor impurity range 1011–1014cm−3, for a constant electric field in the [111] direction. The mathematical treatment is based on Boltzmann's equation, taking account of acoustic phonon scattering and impurity scattering between the different valleys. The electron distribution function in each valley is approximated by a drifted Maxwellian. It is found that the threshold field for the onset of negative differential conductivity increases with increasing impurity concentration and the peak‐to‐valley ratio decreases significantly. The negative differential conductivity region ceases to exist for impurity concentrations larger than 4.5×1013cm−3.

ISSN:0021-8979    

DOI:10.1063/1.1661887

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

We have performed, with the time‐of‐flight technique, an extensive investigation of the transport properties of holes in high‐resistivity CdTe as a function of temperature between 130 and 430 °K and for electric fields between 5 kV/cm and 50 kV/cm. In all investigated samples, at temperatures below 300 °K, the experimental hole mobility decreases on lowering either the temperature or the electric field. These features have been interpreted on the basis of the electric field effect on trapping and detrapping phenomena (Poole‐Frenkel effect) which cause a reduction of the mobility. A critical review of the existing theories of the Poole‐Frenkel effect is presented. The Poole‐Frenkel constant obtained by comparing the experimental data with the most reliable theories of the Poole‐Frenkel effect is in excellent agreement with its theoretical value. By analysis of the experimental data it was also possible to estimate the activation energy (Et=0.14 eV) and the concentration (NT=5×1016cm−3) of the traps which caused the reduction of the mobility. These traps may be due to cadmium vacancies and the value of their concentration found here is in good agreement with previous estimates made in the same material.

ISSN:0021-8979    

DOI:10.1063/1.1661888

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A bakeable time‐of‐flight mass spectrometer has been combined with a novel probe assembly in order to directly investigate the ion species formed prior to and during the flashover of an ultrahigh‐vacuum diode. Species are identified by their known kinetic energy and the time correlation between their arrival at a detector and a high‐voltage pulse applied to the cathode of the diode. By varying the ratio of the pulse amplitude to a positive bias applied to the anode, the extent of ion production in the gap can be probed. Observations at 300 °K and 10−9Torr indicate the presence of both highly charged metal anode ions and adsorbed residual gas prior to flashover. No detected species were formed in the gap, in contrast to what was expected from the results of Davies and Biondi. It is suggested that the absence of such ions may be related to the magnitude of the macroscopic field in the gap, since preliminary observations at flashover show a noticeable change in the nature and abundance of ion species. Electron‐induced desorption appears to be the primary preflashover production mechanism, although field‐enhanced desorption may also be significant.

ISSN:0021-8979    

DOI:10.1063/1.1661889

出版商:AIP    

年代:1973

数据来源: AIP