C. Kusano

Photoconductive imaging using hydrogenated amorphous silicon film

Highly resistive hydrogenated amorphous‐silicon film has been fabricated and examined as blocking‐type photoconductive target of a vidicon‐type image pickup tube. The results indicate that this novel silicon vidicon has many advantages over conventional ones.

Stress Effect on Current-Induced Degradation of Be-Doped AlGaAs/GaAs Heterojunction Bipolar Transistors

The effect of stress on the current-induced degradation of current-voltage characteristics in AlGaAs/GaAs heterojunction bipolar transistors with Be-doped base layers is investigated. Transistors with different orientations of the emitter mesa and different thicknesses of the passivation film are bias tested at room temperature. The results are compared with the stress distributions along the emitter-base junction obtained from a two-dimensional calculation using the boundary element method. It is found that the degradation is caused by the diffusion of Be under high-current density operations and that the flux of Be diffusing from the base layer to the emitter layer is strongly related to the stress distributions around the periphery of the emitter-base junction.

Observation of the Surface Recombination Current with an Ideality Factor of Unity in AlGaAs/GaAs Heterojunction Bipolar Transistors

The surface recombination current with an ideality factor of unity was clearly observed in AlGaAs/GaAs abrupt heterojunction bipolar transistors (HBTs) with the uniform base structure. This was derived from the difference in the base current of HBTs with and without a surface passivation layer of depleted AlGaAs. It had a linear dependence on the emitter mesa perimeter and had no component with an ideality factor of two even at a low base-emitter bias. The results were explained by a simple analysis assuming a high surface recombination velocity.

Influence of Substrate Misorientation on Surface Morphology of Be-Doped GaAs Grown by MBE

The surface morphology of MBE-grown Be-doped GaAs was studied by RHEED, SEM and TEM. {411}A facets were found on the (100) surface for Be 6×1019 cm-3 doping at a growth temperature of 630°C. The surface roughness due to this faceting was suppressed by misorienting the GaAs substrate from (100) toward (111)A; a 19.5° misorientation, i.e., a (411)A substrate, was found to be effective in realizing a smooth surface, even for Be 1×1020 cm-3 doping.

311)A substrates suppression of Be transport during GaAs molecular beam epitaxy

The influence of substrate orientation on Be transport during GaAs molecular beam epitaxy is studied by secondary‐ion mass spectrometry. Substrates are misoriented from (100) toward (111)A, and the epitaxial growth is performed at 630 °C for Be doping at (5–7)×1019 cm−3. Surface segregation and anomalous diffusion similarly depend on substrate orientation. With (311)A orientation, the Be transport is dramatically reduced from its value with conventional (100) orientation. These results are qualitatively explained by considering the effect of atomic steps on the growing surface.

Substrate misorientation effect on be transport during MBE growth of GaAs

The Be transport during MBE growth of GaAs has been studied. The Be surface segregation was clearly separated from the Be diffusion by using misoriented as well as nominal (100) substrates. The Be profiles measured by SIMS showed that the surface segregation was suppressed by the substrate misorientation even when the anomalous diffusion took place. The CAT observation revealed that the Be-induced disordering of superlattices occurred for 6×1019 cm-3 doping. The width of the disordered region was found to depend on the substrate misorientation, which was due to the misorientation dependence of the surface segregation. The step exchange model has been successfully employed to account for these results.

Influence of Substrate Orientation on Be Transport during Molecular Beam Epitaxy of AlGaAs/GaAs Heterojunction Bipolar Transistors

The influence of substrate orientation on Be transport during GaAs molecular beam epitaxy is evaluated by secondary ion mass spectrometry and from the current-voltage characteristics of AlGaAs/GaAs heterojunction bipolar transistors (HBTs). The Be doping level employed is from 2×1019 cm-3 to 9×1019 cm-3. The Be transport for the conventional (100) orientation increases rapidly with the increase of growth temperature (Ts) from 530°C to 630°C. With substrate misorientation from (100) toward (111)A, however, Be transport is decreased at Ts=630°C, and reaches a minimum with (311)A orientation. The maximum current gain of AlGaAs/GaAs HBTs grown at Ts=560°C is 264 for (411)A orientation and 3 for (100) orientation, which confirms the applicability of substrate orientations other than the conventional (100) one for obtaining a sharp Be profile.

Planar AlGaAs/GaAs heterojunction bipolar transistors fabricated using selective W-CVD

The authors describe a planar process for the AlGaAs/GaAs HBTs in which collector vias are buried selectively, even to the base layers, with chemical vapor deposited tungsten (CVD-W) films. By using WF/sub 6//SiH/sub 4/ chemistry, W could be deposited on Pt films, which were overlapped 50 nm thick on the AuGe-based collector electrodes, without depositing W on the surrounding SiO/sub 2/ layers. Current gains of planar HBTs with 3.5- mu m*3.5- mu m emitters were up to 150, for a collector current density of about 2.5*10/sup 4/ A/cm/sup 2/.<<ETX>>

The fabrication process of AlGaAs/GaAs HBTs with low base resistance and low collector capacitance for 10 Gb/s IC chip sets

A fabrication technology for AlGaAs/GaAs HBTs (heterojunction bipolar transistors) with low base resistance and low collector capacitance is developed. Self-aligned AlGaAs/GaAs HBTs show a high cutoff frequency of 45 GHz and maximum oscillation frequency of 70 GHz at collector current of 3.5 mA, and were successfully applied to IC chip sets for 10 Gb/s optical transmission. Among the fabricated 10 Gb/s IC chip sets, an AGC amplifier with 20 dB gain and 13.7 GHz bandwidth and a decision circuit with 66 mVp-p of ambiguity at 10 Gb/s are obtained, which are fully applicable to 10 Gb/s systems.<<ETX>>

Multiple-valued logic application of a triple well resonant tunneling diode

A novel resonant tunneling diode (RTD) with four potential barriers and three quantum wells has been proposed and applied to multiple-valued logic devices. This is the first report of a single diode exhibiting significant double negative differential resistance (NDR) characteristics and operating as a triply stable device with a single supply voltage. The structure of the device is described. It showed significant double NDR between 180 K and room temperature, exhibiting the best characteristics at 219 K; peak/valley current ratios were 2.8 and 1.4 with the same peak currents of 4*10/sup 2/ A/cm/sup 2/ for both NDR peaks. With load resistance of 100 Omega and applied voltage of 1 V, this diode exhibited three stable states at 0.066, 0.158, and 0.249 V, in excellent agreement with numerically simulated values. The numerical simulation also showed that the two resonance voltages can be adjusted independently by varying the width of the wells. This triple-well RTD can realize triple-valued logic devices with a single supply voltage. >