Ioffe Institute Research Articles

Low 1/f Noise in AlGaN/GaN HFETs on SiC Substrates

(a) A. F. Ioffe Institute of Physics and Technology, Russian Academy of Sciences,Polytekhnicheskaya 26, 194021 St. Petersburg, Russia(b) Department of ECSE, Rensselaer Polytechnic Institute, Troy, New York 12180, USA(c) Department of ECE, University of South Carolina, Columbia,South Carolina 29208, USA(d) Microelectronics Laboratory, University of Illinois, Urbana, Illinois 61801, USA(Received July 4, 1999)Experimental results of the low-frequency noise measurements on a large number of differentAlGaN/GaN High Electron Mobility Transistors (HEMTs) grown on sapphire and SiC substrateshave been presented. In the HEMTs grown on sapphire, the 1=f noise is an order of magnitude(or more) higher than for AlGaN/GaN HEMTs grown on SiC substrates. The devices on SiC sub-strates also have higher electron mobility compared to the devices grown on sapphire substrates.The temperature dependence of noise reveals a contribution to the noise from a local level withactivation energy of approximately 0.42 eV for the structures grown on sapphire. A very weaktemperature dependence of the low-frequency 1=f noise found for the wafers grown on SiC is veryimportant for high temperature applications of these devices.

From Röntgen to Ioffe, from Giessen to Saint Petersburg — Relations between Russian and German physics

Two former professors of physics at Giessen university contributed significantly to the development of the Ioffe Institute: Wilhelm Conrad Rontgen as a teacher of Abram Ioffe, and Wilhelm Hanle, whose effect found various applications, e.g., in the spectroscopy of hot electrons in low-dimensional structures. A few examples will illustrate how topics of their scientific work found a continuation in the research activities at Giessen, but also in the collaboration between Giessen and Saint Petersburg. They range from sodium chloride, the old Rontgen/Ioffe material where we could prove the existence of an unusual isotope effect in nickel-doped crystals, over level-crossing experiments in gases, to GaAs/AlAs superlattices, where level-anticrossing spectroscopy of excitons reveals detailed information about recombination processes and interface quality. A short summary of the efforts to keep the traditionally close and good relations between Russian and German physics vital completes the report.

Operation of the TFTR pellet charge exchange diagnostic in the pulse counting mode during H+ radio frequency minority heating

The pellet charge exchange technique on TFTR has been used primarily to obtain active charge exchange measurements using a high-energy (0.5–4.0 MeV) neutral particle analyzer (NPA) in conjunction with impurity pellet injection (Li and B) with the scintillator-photomultiplier detector system operated in the current mode. While passive measurements using pulse counting were also obtained using this instrumentation, operation in this mode was very restrictive with pulse counting rates limited to less than ∼10 kHz in the absence of any significant neutron and gamma induced background signal. An upgrade to a specialized pulse counting capability which was developed by the Ioffe Institute was implemented which consisted of CsI(Tl) scintillators having features designed to minimize signals induced by background neutron and gamma rays and 16-channel pulse height analysis electronics on each of the eight NPA energy channels. Passive measurements of rf-driven energetic hydrogen minority ions which served to verify operation of the pulse counting mode are reported. It is shown that in the passive mode the main donors for the neutralization of H+ ions in this energy range are C5+ ions. The measured effective H+ tail temperatures range from 0.15 MeV at a rf power of 2 MW to 0.35 MeV at 6 MW.

The Maunder Minimum: An Interlaboratory Comparison of Δ14C from AD 1688 to AD 1710

Measurements on same-age tree-ring samples from proximal Ural Mountain trees by the Ioffe Institute research group and at the University of Arizona demonstrate a variance corresponding to a standard deviation of ±5.1% for Ioffe compared to ±2.1% for Tucson. There is also a calibration difference of 4.3 ±1.2 ‰. Comparison of the same years measured in Seattle on wood from the Pacific Northwest shows an offset of 2.2 ± 0.5 ‰. This is not a calibration error, but rather is expected from the well-documented evidence for divergence and upwelling of 14C-depleted CO2 along the west coast of North America.

Quantum wires and dots show the way forward

Concluding his three-part series on the pivotal role of compound semiconductor heterostructures, Professor Alferov of the Ioffe Institute in St. Petersburg reviews the development and recent exciting advances in quantum wires and, in more detail, quantum dot structures. The future trends and perspectives of these new types of heterostructures are discussed.

High energy neutral particle analyzer

The paper describes a high energy neutral particle analyzer (HENPA) developed in the Ioffe Institute for the diagnostics of alpha particles in the megaelectronvolt energy range, as well as other charged fusion products and ion cyclotron resonance frequency-driven minority ions in a plasma. Megaelectronvolt ions can be neutralized in the plasma by charge exchange reactions with low energy atoms or impurity ions, and by recombination. The density of target particles for neutralization can be increased in the plasma by neutral beam or pellet injection. The operation of the HENPA is based on stripping megaelectronvolt atoms by means of a carbon foil, and subsequent E | B analysis of secondary ions. Eight (or 2 × 8, depending on the version) detectors that consist of (CsI + TI) scintillators 2–25 μm thick optically coupled to photomultiplier tubes are used to detect secondary ions. The detection efficiency of the detectors for megaelectronvolt ions is close to 100%; it drops to 10 −4 − 10 −8 for D-T neutrons, and to much lower values for D-D neutrons and gamma quanta in the energy range above 1 MeV. The HENPA is calibrated using megaelectronvolt H 0-He 0 beams from the cyclotron, starting from 0.4 MeV for He 0 and 0.1 MeV for H. The energy ratio of simultaneously detected particles is E max E min ≈ 4 . The energy widths of the channels are 6%–15%. The HENPA can operate in a stray magnetic field up to 0.07 T. Some examples of results obtained by the HENPA are presented.

Multipass/multipulse Thomson scattering on CDX-U (abstract)

A multipass/multipulse Thomson scattering system has been implemented on CDX-U in collaboration with the Ioffe Institute, St. Petersburg. The system consists of a low energy (1.5– 2.5 J), passively Q-switched ruby laser, and a multipass optical cavity enclosing the plasma. Multiple reflections of the beam within the cavity increase by about an order of magnitude the number of scattered photons, allowing temperature density to be measured with good accuracy even at very low plasma density. By feeding the returned beam back into the laser, the system can deliver several pulses over a 1 ms period. However, the experiments on CDX-U show that a mechanical shock wave reaching the multipass system affects the feedback and laser output per pulse drops significantly. Therefore we operate the system by fine tuning the laser cavity, so that output is practically independent of feedback from multipass cavity. Also, by optimizing the transmission of the passive Q-switch and the pumping power, we obtain that laser output is concentrated in single large pulse of 2–2.5 J energy. We achieve circulating energy in the plasma in excess of 12 J per pulse, while minimizing at the same time stray light. As shown by results from CDX-U, this enables in some cases better than 10% accuracy, despite relatively low plasma density conditions.

The railgun experiments on head-on collision of different mass bodies in 10-15 km/s range

Existing techniques allow the launch of solid imparters up to only about 10 km/s. A way of doubling the effective velocity for collision experiments is to use two accelerators to produce a head-on collision. However, light-gas guns and conventional EM launchers with pre-accelerators are not suitable for this mode of operation due to the difficulty of synchronizing the projectile motion when travelling through long bores (from a few meters to tens of meters). The compacted plasma armature railgun (RG) developed at the Ioffe Institute has a much shorter bore because it operates at a constant-along-the-barrel acceleration close to the maximum value allowed by the projectile strength or electrothermal explosion of rails. Acceleration of a typical 1 cm body reaches /spl sim/1-5 MGees, so that 7 km/s is achieved in 56 cm bore. The short acceleration length makes it possible to synchronize the motion in two counter-firing RGs. We have done experiments with two sets-ups, one using two RGs having identical square bores of 2 mm across and the other using an 8 mm square bore RG opposed to a 2 mm bore. Exploiting a rotating-mirror camera and a laser we have photographed collision processes at relative velocities of 4.9+5.1=10 km/s and 5.9+4.5=10.4 km/s, respectively. The potentials of this approach are far from being exhausted.

Anisotropic cooling and atmospheric radiation of neutron stars with strong magnetic field*

Annals of the New York Academy of SciencesVolume 759, Issue 1 p. 291-294 Anisotropic cooling and atmospheric radiation of neutron stars with strong magnetic field* Yu. A. SHIBANOV, Yu. A. SHIBANOV Ioffe Institute of Physics and Technology 194021, St. Petersburg, RussiaSearch for more papers by this authorG. G. PAVLOV, G. G. PAVLOV Pennsylvania State University University Park, PA 16802, USASearch for more papers by this authorV. E. ZAVLIN, V. E. ZAVLIN MPI für Extraterrestrische Physik D-85740 Garching, GermanySearch for more papers by this authorL. QIN, L. QIN Montana State University Bozeman, MT 59717, USASearch for more papers by this authorS. TSURUTA, S. TSURUTA Montana State University Bozeman, MT 59717, USASearch for more papers by this author Yu. A. SHIBANOV, Yu. A. SHIBANOV Ioffe Institute of Physics and Technology 194021, St. Petersburg, RussiaSearch for more papers by this authorG. G. PAVLOV, G. G. PAVLOV Pennsylvania State University University Park, PA 16802, USASearch for more papers by this authorV. E. ZAVLIN, V. E. ZAVLIN MPI für Extraterrestrische Physik D-85740 Garching, GermanySearch for more papers by this authorL. QIN, L. QIN Montana State University Bozeman, MT 59717, USASearch for more papers by this authorS. TSURUTA, S. TSURUTA Montana State University Bozeman, MT 59717, USASearch for more papers by this author First published: September 1995 https://doi.org/10.1111/j.1749-6632.1995.tb17547.xCitations: 11 † This work was partialy supported by Russian Foundation of Fundamental Researches (grant 93–02–2916), by ESO C&EE (grant A-01–068), by ISF (grant R6A000), by NASA grants NAG5–2807 and NAGW-2208, and by Visiting Program of MPE. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume759, Issue1Seventeenth Texas Symposium on Relativistic Astrophysics and CosmologySeptember 1995Pages 291-294 RelatedInformation

Using large spread films for destruction and elimination of anthropogenic debris in space

As follows from experiments, including those performed in the Ioffe Institute, the collision of a body with an object of ∼ 10 3 smaller mass moving at 7–10 km/s leads to catastrophic disruption of the body accompanied by its partial evaporation. As a result, an effective way to eliminate low-orbit debris could be to launch large film surfaces into appropriate orbits. The use of a large surface to brake debris (∼ 2% velocity decrease) and lower it into denser parts of the atmosphere has been considered earlier. However, there are grounds to believe that the destruction of the orbital debris into smaller fragments together with partial evaporation will prove to be a more effective and lower cost solution. At the same time, the film thickness is also reduced, being only ∼ 10 −3 of the dimension of the body to be disrupted: to eliminate bodies with diameters < 3 cm during a 20 yr period one needs only to launch a ∼ 20 μm spread film of ∼ 1, 000 ton in total. In order to elaborate details of the program and to determine an optimal strategy for its realization, it is only natural that a great deal of preliminary work is needed, including studies on hypervelocity impacts at 10–15 km/s. Our achievements in hypervelocity EM launching and head-on collision of bodies provide grounds to hope that experiments in this velocity range will begin in the near future.

II. Experimental Hall effect data for amorphous semiconductors

Abstract This paper presents the main features of the experimental data on Hall effect measurements in amorphous semiconductors reported so far. More specially, it analyses data on chalcogenide glasses, tetrahedral CdGe x As2 glasses and amorphous germanium, silicon and arsenic. Kolomiets and his group at the Ioffe Institute of Leningrad were the first to study systematically the properties of amorphous semiconductors. Kolomiets and Nazarova (1960) published the first experimental work on the Hall effect in chalcogenide glasses, having examined vitreous materials of the Tl2SeAs2(SeTe)3 system II. Two features of great interest emerged from this work. The first is the magnitude of the Hall mobility, which was found to be a few times 10−l cm2 V−1 s−1 throughout; the second is the sign anomaly of the Hall coefficient, i.e. n-type Hall coefficient but p-type Seeback coefficient. Eighteen years later these features still represent the principal differences between Hall effect results on amorphous, as compared ...

Hot excitons in cadmium selenide

physica status solidi (b)Volume 18, Issue 1 p. K37-K40 Short Note Hot excitons in cadmium selenide B. S. Razbirin, B. S. Razbirin Institute of Experimental Physics, University of Warsaw On leave from the A.F. Ioffe Institute of Technical Physics, Academy of Sciences of the USSR, Leningrad.Search for more papers by this authorI. Filinski, I. Filinski Institute of Experimental Physics, University of WarsawSearch for more papers by this authorB. Wojtowicz-Natanson, B. Wojtowicz-Natanson Institute of Experimental Physics, University of WarsawSearch for more papers by this author B. S. Razbirin, B. S. Razbirin Institute of Experimental Physics, University of Warsaw On leave from the A.F. Ioffe Institute of Technical Physics, Academy of Sciences of the USSR, Leningrad.Search for more papers by this authorI. Filinski, I. Filinski Institute of Experimental Physics, University of WarsawSearch for more papers by this authorB. Wojtowicz-Natanson, B. Wojtowicz-Natanson Institute of Experimental Physics, University of WarsawSearch for more papers by this author First published: 1966 https://doi.org/10.1002/pssb.19660180154Citations: 6 AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume18, Issue11966Pages K37-K40 RelatedInformation