Igor V. Grekhov

Silicon Auger transistor—New insight into the performance of a tunnel MIS emitter transistor

An experimental study of the silicon tunnel MIS emitter transistor characteristics shows that tunneling hot electrons produce Auger ionization in the collector layer. This effect is responsible for a high value and a multistep sharp rise of current gain and for multistable S-shape collector characteristics in common emitter operation. A possible modification of the transistor structure is a transistor with a metal (or superconducting) base layer. The Auger ionization probability near threshold in Si has been studied by using an Auger transistor structure.

ZnO/GaN heterostructure for LED applications

White electroluminescence (EL) from ZnO/GaN structures fabricated by pulsed laser deposition of Zn:In onto GaN:Mg/GaN structures MOCVD-grown on Al2O3 substrates has been observed. The white light is produced by superposition of two strongest emission lines, narrow blue and broad yellow, peaked at 440 and 550 nm, respectively. The intensity ratio of different EL lines from ZnO/GaN/Al2O3 structures depends on the ZnO film quality and drive current. The white EL is due to the high density of structural defects at the n-ZnO/p-GaN interface. A band diagram of the n-ZnO/p-GaN/n-GaN is constructed and a qualitative explanation of the EL is given. Conditions of ZnO deposition strongly affects the properties of the recombination emission and predetermines the EL spectrum of the LED structure if it does not have high quantum efficiency (more than 1%) such as in commercial LEDs.

Dynamic avalanche breakdown of a p‐n junction: Deterministic triggering of a plane streamer front

We discuss the dynamic impact ionization breakdown of a high voltage p‐n junction which occurs when the electric field is increased above the threshold of avalanche impact ionization on a time scale smaller than the inverse thermogeneration rate. The avalanche-to-streamer transition characterized by generation of dense electron-hole plasma capable of screening the applied external electric field occurs in such regimes. We argue that the experimentally observed deterministic triggering of the plane streamer front at the electric-field strength above the threshold of avalanche impact ionization, yet below the threshold of band-to-band tunneling, is generally caused by field-enhanced ionization of deep-level centers. We suggest that the process-induced sulfur centers and native defects such as EL2, HB2, and HB5 centers initiate the front in Si and GaAs structures, respectively. In deep-level-free structures the plane streamer front is triggered by Zener band-to-band tunneling.

Theory of superfast fronts of impact ionization in semiconductor structures

We present an analytical theory for impact ionization fronts in reversely biased p+-n-n+ structures. The front propagates into a depleted n base with a velocity that exceeds the saturated drift velocity. The front passage generates a dense electron-hole plasma and in this way switches the structure from low to high conductivity. For a planar front we determine the concentration of the generated plasma, the maximum electric field, the front width, and the voltage over the n base as functions of front velocity and doping of the n base. The theory takes into account that drift velocities and impact ionization coefficients differ between electrons and holes, and it makes quantitative predictions for any semiconductor material possible.

Physical basis for high power semiconductor nanosecond opening switches

The authors describe how, as a result of long-time research and development, a very high power, repetitive mode, semiconductor-based nanosecond technique is now commercially available. Drift step recovery diodes and inverse recover diodes are preferable as a base for generators with pulse rise times of 0.5-3 ns and pulse powers less than 50-80 MW. Silicon opening switch diodes are preferable at pulse rise times higher than 5 ns with any power and at any pulse rise time if the pulse power is higher than 100 MW.

INTERFACIAL PROPERTIES OF SILICON STRUCTURES FABRICATED BY VACUUM GROOVED SURFACE BONDING TECHNOLOGY

The paper presents a novel modification of a direct bonding technology. A presented innovation is aimed at fabricating void free interfaces with a low defect density. For this purpose the bonding boundaries are manufactured as grooved, and the bonding annealing is performed under vacuum conditions. It has been found that the grooves act as dislocation traps. A trapped gas escapes through the grooves which facilitates the void removal. By X-ray and electron diffraction techniques the grooves have been observed to flatten rapidly. The electrical properties of the grooved interfaces are as good as those of diffusion p-n junctions.

Performance evaluation of picosecond high-voltage power switches based on propagation of superfast impact ionization fronts in SiC structures

We employ a simple analytical model of superfast impact ionization front in a reversely biased p+-n-n+ structure to evaluate the performance of prospective 4H-SiC closing switches based on propagation of ionization fronts. The model allows to relate the order of magnitude values of the front velocity and the electron-hole plasma concentration behind the front to the basic material and structural parameters. We show that high avalanche breakdown field and impact ionization rate of the wide-band-gap 4H-SiC lead to dramatic improvement of switching characteristics with respect to Si structures currently used in pulse power applications. The concentration of electron-hole plasma generated by the front passage is of the order of 1018 versus 1016cm−3 in Si. The velocity of ionization front in 4H-SiC is several times larger than in Si. Finally, we discuss possible triggering mechanisms for the ionization front in SiC.

Impact ionization fronts in semiconductors: Numerical evidence of superfast propagation due to nonlocalized preionization

We present numerical evidence of superfast propagation of ionizing fronts that occurs due to nonlocalized preionization of the depleted high-field region. In nonlinear dynamics terms, this traveling front mode of avalanche breakdown in a semiconductor corresponds to a pulled front propagating into an unstable state in the regime of nonlocalized initial conditions. Our simulations reveal excitation and propagation of such fronts in a Si p+-n-n+ structure. The front is triggered by applying a sharp voltage ramp to a reversely biased structure. Before the front starts to travel, field-ehanced emission of electrons from deep-level impurities preionizes initially depleted n base creating spatially nonuniform profile of free carriers. Impact ionization takes place in the whole high-field region the front propagates to. We find two ionizing fronts that propagate in opposite directions with velocities up to ten times higher than the saturated drift velocity.

Impact ionization fronts in semiconductors: Superfast propagation due to nonlocalized preionization

We present a theoretical study of impact ionization fronts propagating into semiconductor with a constant electric field Em in presence of a small concentration of free nonequilibrium carriers—so-called preionization. We show that if this concentration decays in the direction of the front propagation with a small characteristic exponent λ, the front velocity is determined by vf≈2βm∕λ, where βm≡β(Em) is the corresponding ionization frequency. The propagation velocity vf can exceed the saturated drift velocity vs by several orders of magnitude even in moderate electric fields.

TRANSPARENT FERROELECTRIC FIELD EFFECT TRANSISTOR WITH A SINGLE-CRYSTAL SnO2 CHANNEL

ABSTRACT The possibility of fabrication of a transparent ferroelectric field effect transistor (FFET) with a high electron mobility channel was demonstrated. The highest obtained electron mobility in the channel SnO2/c-Al2O3 is 25 cm2/V·s and SnO2/r-Al2O3 is 40 cm2/V·s at the electron density of 1019–1020 cm−3. A transparent FFET structure Au/PZT/SnO2/Al2O3 has been fabricated. The best sample had 94% conductivity modulation at the gate voltage from −5 V to 2 V. The difference in the channel current at positive and negative remnant polarizations of the undergate ferroelectric is 37%.