L. S. Kostina

Investigation of dislocations in Czochralski grown Si1−xGex single crystals

Dislocations in p-type Si1−xGex single crystals (2‐8 at% Ge) grown with the Czochralski technique are investigated by synchrotron white beam topography in transmission geometry. As the Ge concentration increases, the dislocation structure evolves from individual dislocations to slip bands and sub-grain boundaries, and the dislocation density increases from <10 2 cm −2 to 10 5 ‐10 6 cm −2 at 8at%. We discuss the effect of dislocations on the electrical characteristics such as resistivity ρv, Hall hole mobility µp, carrier lifetime τe and I‐V characteristics. Here τe and I‐V characteristics are measured from the diodes fabricated by bonding the p-Si1−xGex to n-Si wafers. I‐V characteristics are not deteriorated in spite of a five times decrease in τe with the Ge concentration.

Current-voltage characteristics of Si/Si1 − xGex heterodiodes fabricated by direct bonding

We have studied the current-voltage (I–U) characteristics of Si/Si1 − xGex (0.02 < x < 0.15) heterodiodes fabricated by direct bonding of (111)-oriented n-type single crystal silicon wafers with p-type Si1 − xGex wafers of the same orientation containing 2–15 at % Ge. An increase in the germanium concentration NGe in Si1 − xGex crystals is accompanied by a growth in the density of crystal lattice defects, which leads to a decrease in the minority carrier lifetime in the base of the heterodiode and an increase in the recombination component of the forward current and in the differential resistance (slope) of the I–U curve. However, for all samples with NGe ≤ 15 at %, the I–U curves of Si/Si1 − xGex heterodiodes are satisfactory in the entire range of current densities (1 mA/cm2–200 A/cm2). This result shows good prospects for using direct bonding technology in the fabrication of Si/Si1 − xGex heterostructures.

Emission intensity in the visible and IR spectral ranges from Si-based structures formed by direct bonding with simultaneous doping with erbium (Er) and europium (Eu)

The photo- and electroluminescence spectra of silicon-based structures formed by direct bonding with simultaneous doping with rare-earth metals are studied. It is shown that emission in the visible and IR spectral ranges can be obtained from n-Si:Er/p-Si and n-Si:Eu/p-Si structures fabricated by the method suggested in the study. The results obtained make this method promising for the fabrication of optoelectronic devices.

Reverse recovery of Si/Si1 − xGex heterodiodes fabricated by direct bonding

We have studied the process of reverse recovery of Si/Si1 − xGex heterodiodes fabricated by direct bonding of (111)-oriented n-type single crystal silicon wafers with p-type Si1 − xGex wafers of the same orientation containing 4–8 at. % Ge. An increase in the germanium concentration NGe in p-Si1 − xGex layer is accompanied by a decrease in the reverse recovery time of heterodiodes. The presence of a sharp drop in the reverse current on the diode recovery characteristic can be explained by the existence of a narrow region with decreased minority carrier lifetime at the bonding interface (compared to carrier lifetime in the bulk), which is caused by the accumulation of misfit dislocations (generated by bonding (in this region). The results demonstrate the principal possibility of creating fast-recovery diodes based on the Si/Si1 − xGex heterosystem for high-power semiconductor devices manufactured using the direct bonding technology.

Ultrafast turn-off of high currents by field-controlled integrated thyristor

The turn-off process in a powerful high-voltage switch of the new type, integrated thyristor controlled by an external MOSFET, has been studied. Dynamic characteristics were measured in high current turn-off regimes, in which plasma is removed by the full device current. The limiting density of switched current amounted to 600 A/cm2. The regime with short circuit of several dozen thousand parallel operating microthyristor cells is quite effective, ensuring a current decay time of about 40 ns, which is several times as small as that in all other types of high-voltage switches for working voltages above 1.5 kV.

Structural and electrical properties of SiGe-on-insulator substrates fabricated by direct bonding

A new method for fabricating SiGe-on-insulator substrates, i.e., direct bonding of thermally oxidized Si wafers with Si1 − xGex wafers cut from Czochralski-grown crystals, is suggested. Si1 − xGex layers no larger than 10 μm thick in SiGe/SiO2/Si compositions were fabricated by chemical mechanical polishing. To increase the Ge content in the Si1 − xGex layer, thermal oxidation was used. It was shown that the increase in the Ge content and heat treatment procedures at 1250°C are not accompanied by degradation of structural and electrical characteristics of Si1 − xGex layers.

Fabrication of high quality SOI bonding materials by modified direct wafer bonding technique

A modified direct bonding technique employing a deposition on a wafer to be bonded of silica coating is proposed for the fabrication of Si-SiO/sub 2/-Si structures. The structural and electrical quality of bonded compositions is studied. Satisfied insulating properties of interfacial SiO/sub 2/ layer are demonstrated. Elastic strain caused by surface morphology in the structures with smooth and artificially grooved interfaces is investigated. The diminution of strain in the grooved structures is semi quantitatively interpreted by a model considering the virtual defects distributed over the interfacial region.

The formation of shallow-donor distribution profiles in proton irradiation of silicon

A study of the formation of shallow hydrogen-containing donors (hydrogen-related shallow thermal donors, STD(H)) in silicon under proton irradiation followed by annealing in a temperature range of 300–500°C is reported. The effect of postimplantation annealing regimes on the concentration distribution of shallow donors at various proton energies and fluences is examined. It is shown that the shape of the concentration profiles strongly varies with temperature and annealing duration when a fixed concentration of radiation defects is introduced and equally with energy and dose at a given annealing temperature. It is also shown that the process in which hydrogen-containing shallow donors are formed is accompanied by the appearance in n-type silicon of H-induced buried n′-layers, the formation of which near the pn junction in the high-resistivity n-base of diode structures allows the breakdown voltage of high-voltage pn junctions to be controlled. In the general case, this makes it possible to improve the characteristics of power silicon devices of various purposes.

Electron irradiation controlled profile of recombination center concentration in silicon

It is shown that the axial distribution of the recombination center concentration in high-voltage silicon p+Nn+ diodes can be controlled by electron irradiation in a certain energy range. Results of investigations of the main static and dynamic characteristics of electron-irradiated diodes are presented.

SiC-Si Grooved Surface Bonding

SiC Lely platelets and SiC epilayers on large area SiC substrates were directly bonded to non-oxidized grooved surface silicon wafers in order to obtain structures prospective for the design of power bipolar devices with wide band-gap emitter junctions. The reported capabilities of grooved interfaces to reduce elastic strain and intrinsic sources of an interfacial potential barrier were utilized. The influence of surface morphology on the structural perfection of the bonded samples was studied in detail by X-ray and AFM techniques. As compared to traditional bonding technology, experimental data showed an easier smooth-to-grooved surface bonding accomplished in the formation of the boundary with better continuity and strength. For 2 in. diameter SiC wafers with root mean square height of roughness σ=16 A and lateral coherence length L =1.8 μm bonding continuity not smaller than 90% was reached, while the crystals with σ=30 A, L =5 μm failed to bond to Si even under an external force.