Katsuhiko Mitani

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.

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>>

GaAs radiation damage induced by electron cyclotron resonance plasma etching with SF6/CHF3

After SF6/CHF3 plasma exposure, the sheet resistance of Si-doped GaAs layers is higher because of carrier reduction near the surface and sputter etched surface, and this electrical and physical damage is found to depend on rf-power and µ-wave power. The carrier reduction can be almost restored by annealing at 450° C for 30 min. Exposures to He plasma or CHF3 plasma cause more extreme carrier reduction than does exposure to SF6 plasma, indicating that the carrier reduction in the damaged layers is predominantly due to the bombardment by low-mass fragments such as H and He. Low-temperature (4.2 K) photoluminescence of SF6/CHF3-plasma-exposed GaAs shows a broad and complicated spectrum (ranging from 1.25 to 1.43 eV) related to defect-complex by incorporation of hydrogen.

The Effect on Turn-On Voltage (VBE) of AlGaAs/GaAs HBT's due to the Structure of the Emitter-Base Heterojunction

The effects on the turn-on voltage (VBE) of collector current in AlGaAs/GaAs HBTs due to Be diffusion and discontinuity in the conduction band are investigated. It is clarified that VBE increases significantly with the decrease in saturation current due to Be diffusion into the AlGaAs emitter during MBE growth. It is also found that the VBEs of HBTs with Al compositionally abrupt and graded emitter-base junctions and homojunction GaAs bipolar transistors are the same. These results indicate that the spike-like potential barrier at the heterojunction has no influence on the electron injection from emitter to base.

Damage induced by exposing AlGaAs layers to electron cyclotron resonance SF6/CHF3 plasma

We investigated the damage induced by exposing AlxGa1−xAs (x=0.30, 0.15) and GaAs layers to electron cyclotron resonance SF6/CHF3 plasma and the repair of this damage by annealing. After plasma exposure the sheet resistance of all these samples is higher because of carrier reduction near the surface. This kind of damage in AlxGa1−xAs (x=0.15) and GaAs can be restored by annealing at 450 °C for 30 min. The plasma‐damaged AlxGa1−xAs (x=0.30), however, has a further increased sheet resistance after annealing, and the sheet resistance AlxGa1−xAs (x=0.3), not exposed to the plasma is unaffected by annealing. Capacitance‐voltage measurements show that annealing causes the carrier reduction in plasma‐exposed AlxGa1−xAs (x=0.30), to extend to a greater depth.

AlGaAs/GaAs HBTs for 10-Gb/s ICs using a new base ohmic contact fabrication process

A new basic ohmic contact technology for AlGaAs/GaAs heterojunction bipolar transistors (HBTs) is presented. The effect of the device parameters on the high-frequency performance of HBT ICs for 10-Gb/s systems is analyzed, and it is shown that, at a cutoff frequency (f/sub T/) of 40 GHz or more, reducing base resistance or collector capacitance is more effective than increasing f/sub T/ for obtaining high-frequency performance. A process is developed for fabricating base electrodes with a very low ohmic contact resistivity, approximately 10/sup -7/ Omega -cm/sup 2/, by using a AuZn/Mo/Au alloy, which provides the required high performance. Self-aligned AlGaAs/GaAs HBTs, with a 2.5- mu m*5- mu m emitter, using a AuZn/Mo/Au alloy base metal and an undoped GaAs collector, are shown to have an f/sub T/ and a maximum oscillation frequency of about 45 and 70 GHz, respectively, at 3.5 mA. An AGC amplifier with a 20-dB gain and a bandwidth of 13.7 GHz demonstrates stable performance. >

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>>