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Effects of isolation materials on facet formation for low temperature Si selective epitaxial growth (SEG) using Si2H6 have been demonstrated by ultrahigh vacuum-chemical molecular epitaxy (UHV-CME) system. The activation energy of the Si epitaxial growth is 47.35 Kcal/mol. The isolation material includes silicon nitride, wet oxide, and tetraethylorthosilicate (TEOS) oxide. Different isolation materials have different faceting behaviors for the Si epilayer. A silicon nitride mask and a wet oxide mask result in a preferred faceting plane of (111) and (311), respectively. Using a TEOS oxide mask, we obtain a low temperature Si SEG layer without facet and twin formation. The preferred faceting plane orientation for different isolation materials is ascribed to the difference in the interface free energy between the Si layer and the isolation material.

The self‐aligned formation of CoSi2 was achieved on the selective epitaxial growth (SEG) silicon layer on (001)Si inside 0.1–0.6 μm oxide openings prepared by electron beam lithography. The uniform, high quality SEG Si layer was grown by ultrahigh vacuum chemical vapor deposition at 560 °C with Si2H6. Self‐aligned CoSi2 film without lateral growth of silicide was grown on the SEG Si layer by rapid thermal annealing at 700 °C in N2 ambient. The successful integration of the self‐aligned CoSi2 and SEG of Si processes promises to be a viable process technology for the future deep submicron devices.

A P‐n‐p AlGaAs/InGaAs/GaAs collector‐up heterojunction bipolar transistor (C‐up HBT), grown by three‐stage molecular beam epitaxy, has been fabricated, and its dc and high‐frequency performances have been evaluated. The use of a graded InxGa1−xAs (x=0.0–0.09) is shown to improve the common‐emitter current gain (β) and to greatly reduce the base transit time (τb) for the P‐n‐p C‐up HBTs. A maximum current gain (β) of 150 was measured for a 16×17 μm2 device. From S‐parameter measurements, a best unity‐gain cutoff frequency fT=43 GHz at a collector current of −10 mA was achieved using a 5×10 μm2 collector area. The results show that the P‐n‐p C‐up HBTs may be useful for future planar integrated circuit applications.

An Al0.25Ga0.75As/In0.08Ga0.92As/GaAs heteroemitter bipolar transistor (HEBIT) with a uniformly high common‐emitter current gain (β) of 500 was demonstrated for the first time. Using a simple chemical treatment [P2S5/(NH4)2S], we have greatly reduced the surface recombination in the emitter‐base junction perimeters, resulting in a tenfold increase in the maximum current gain of the device at low collector currents. InGaAs nonalloyed ohmic contacts were also employed to form both emitter and base electrodes in a one‐step process. To evaluate the performance of the HEBIT, we conducted current‐voltage measurements and compared the Gummel plots at 300 and 77 K.