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We conducted an investigation of line-shaped defects, extending in the 〈010〉 direction, in bulk β-Ga2O3single crystals grown by the vertical Bridgman (VB) method. Parallelepiped cross-section samples with {010} polished surfaces and {100} cleavage planes were prepared and were then etched in phosphoric acid at 140 °C. Rhombic etch pits were observed on the (010) surface and they were similar in shape to those reported as nanometer-sized grooves or plate-like nanopipes in crystals grown by the edge-defined film-fed growth (EFG) method. Groove-like voids in the 〈010〉 direction were also observed on {100} cleavage planes below the etch pits observed on the {010} surface. Therefore, we concluded that line-shaped defects observed in VB-grown crystals are similar to defects observed in EFG-grown crystals. The size of these defects was considerably smaller than that observed in EFG-grown crystals, but with a density of 5 × 105 cm−2. Based on these results, possible formation mechanisms for such defects were discussed.

A GaAs four-channel digital time switch LSI with a 2.0-Gb/s throughput is developed. This switch consists of 4-bit shift registers, data latches, a counter, a control unit, and 1/0 buffer gates. The LSI includes 1176 devices (FET's, diodes, and resistors) and its equivalent gate number is 231 gates. Low Power Source Coupled FET Logic (LSCFL) operating in a true/complementary mode is used to ensure high-speed and low-power performance. MESFET's with 0.55-µm gate length are fabricated by the buried p-layer SAINT process, which satisfactorily suppresses short channel effects. Dislocation-free wafers are also used to provide high chip yields of 75 percent. The propagation delay time of the LSCFL basic circuit is 48 ps/gate with 1.4-mW/equivalent gate. The total power dissipation including input and output buffers is 0.64 W. The LSI speed performance is evaluated by measuring toggle frequency of the 1/4 frequency divider. The divider operates typically at 5.1 GHz, maximum 7.5 GHz. The newly developed high-speed digital time switch LSI makes possible time division switching services in TV and high-definition TV transmission systems.

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We intend to use diamond film as sensors for pressure, strain and acceleration. For this purpose, a new process was developed to produce a bridge structure of diamond film using sacrificial layer etching and selective growth by ion implantation. The size of the bridge made by this process is 240 × 420 μm2and the thickness is about 3.5 μm. Bending displacement of the bridge under various loads between 1 mgf and 40 mgf is studied. The maximum displacement is proportional to the load and is about 0.2 μm at 40 mgf loading. As a result, Young's modulus of the diamond film is estimated to be about 1000 GPa.