GaAs OM CVD MESFET

Abstract

Al gate self aligned schottky barrier field effect transistors having gate dimensions of 1.5µ × 300µ and a channel length of 3µ were fabricated in epitaxial layers grown by organometallic chemical vapor deposition. The layers with a net carrier concentration of 1.4 × 1017cm-3were grown at 730°C. The devices exhibited a maximun dc transconductance (g m ) of about 30 mmhos. The g m degradation near the substrate interface appeared to be less than the comparable unbuffered vapor phase epitaxy (VPE) layers. The velocity profile into the active channel layer deduced from the dc performance of the devices indicated an average electron velocity of 1.3 × 107cm/sec which is the same as VPE material. The velocity degraded region was confined to within about 350 A of the interface. This compares with about 500 A in the unbuffered and about 200 A in the buffered VPE material. A maximum available microwave gain of 10 dB and a noise figure of 3 dB with an associated gain of 5 dB at 8 GHz were measured. Those results are excellent considering the gate length of 1.5µ. Small-signal scattering parameters were measured and the equivalent circuit parameters were calculated. Devices having 0.5µ × 140µ gate dimensions are currently being fabricated. Any results on 0.5µ gate devices,and the performance of 1.5µ gate devices will be discussed. In the light of the above results, it is concluded that the OM-CVD technique may be capable of producing high quality FET material much faster than VPE and at a lower cost.