Dynamic avalanche breakdown of a p-n junction: deterministic triggering of a plane streamer front

We discuss the dynamic impact ionization breakdown of 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 to screen 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 but 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, 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.Comment: 4 pages, 2 figure

Electronic structure of GaAs1-xNx alloy by soft-X-ray absorption and emission: Origin of the reduced optical efficiency

The local electronic structure of N atoms in a diluted GaAs1-xNx (x=3%) alloy, in view of applications in optoelectronics, is determined for the first time using soft-X-ray absorption (SXA) and emission (SXE). Deviations from crystalline GaN, in particular in the conduction band, are dramatic. Employing the orbital character and elemental specificity of the SXE/SXA spectroscopies, we identify a charge transfer from the N atoms at the valence band maximum, reducing the overlap with the wavefunction in conduction band minimum, as the main factor limiting the optical efficiency of GaAs1-xNx alloys. Moreover, a k-conserving process of resonant inelastic x-ray scattering involving the L1 derived valence and conduction states is discovered.Comment: 3 pages, physica status solidi (Rapid Research Notes), in pres

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. 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.Comment: 18 pagers, 10 figure

Tunneling-assisted impact ionization fronts in semiconductors

We propose a novel type of ionization front in layered semiconductor structures. The propagation is due to the interplay of band-to-band tunneling and impact ionization. Our numerical simulations show that the front can be triggered when an extremely sharp voltage ramp ($\sim 10 {\rm kV/ns}$) is applied in reverse direction to a Si $p^+-n-n^+-$structure that is connected in series with an external load. The triggering occurs after a delay of 0.7 to 0.8 ns. The maximal electrical field at the front edge exceeds $10^6 {\rm V/cm}$. The front velocity $v_f$ is 40 times faster than the saturated drift velocity $v_s$. The front passes through the $n-$base with a thickness of $100 {\mu m}$ within approximately 30 ps, filling it with dense electron-hole plasma. This passage is accompanied by a voltage drop from 8 kV to dozens of volts. In this way a voltage pulse with a ramp up to $500 {\rm kV/ns}$ can be applied to the load. The possibility to form a kilovolt pulse with such a voltage rise rate sets new frontiers in pulse power electronics.Comment: 12 pages, 6 figure

Stimulated emission of radiation using spin-population inversion in metals: a spin-laser

Arrays of 10 nm-diameter point contacts of exchange-coupled spin-majority/spin-minority ferromagnetic metals, integrated into infrared-terahertz range photon resonators, are fabricated and measured electrically and optically. Giant, threshold-type electronic excitations under high-current pumping of the devices are observed as abrupt but reversible steps in device resistance, in many cases in access of 100%, which correlate with optical emission from the devices. The results are interpreted as due to stimulated spin-flip electron-photon relaxation in the system.Comment: 5 page

Stoichiometry and absolute atomic concentration profiles obtained by combined Rutherford backscattering spectroscopy and secondary-ion mass spectroscopy: InAs nanocrystals in Si

Abstract Rutherford backscattering spectroscopy (RBS) and secondary-ion mass spectroscopy (SIMS) were combined to achieve depth profiling calibrated in absolute atomic concentrations. This method was applied to InAs nanocrystals, grown by molecular beam epitaxy (MBE), buried in a Si matrix. By means of RBS, with its capability of accessing the buried layers, we determined the depth-integrated areal densities of As and In. These were used to calibrate the SIMS profiles with their high depth resolution and dynamic range in absolute atomic concentrations. This allowed us to identify, besides a well confined layer of stoichiometric InAs nanocrystals, significant diffusion of In and As into the Si matrix in despite of their larger atomic radii, and an excess of As due to its non-reactive deposition on Si from the excess As 4 flux during the MBE growth. On the basis of these findings, we suggest measures to optimize the MBE process for InAs/Si and similar systems