H. Morkoc

Contact potential of p-Al0.5Ga0.5As/n-GaAs structures

Abstract The built-in potential of Al 0.5 Ga 0.5 As (10 18 cm −3 ) gates on n -type (10 17 cm −3 ) GaAs channel layers in the case of heterojunction normally-off FETs has been measured via C - V and forward I - V methods. A built-in potential of 1.39 eV from C - V measurements and 1.36 eV from forward I - V characteristics which compare well with the theory (1.4 eV) have been deduced. The ideality coefficient is found to be 1.56.

GaAs OM CVD MESFET

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 (gm) of about 30 mmhos. The gmdegradation 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 Å of the interface. This compares with about 500 Å in the unbuffered and about 200 Å 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.

MP-A7 microwave In x Ga 1-x As y P 1-y /Inp MESFET

circuit in order to insure input-output voltage compatibility. A moderate power savings, 33 percent, was achieved in circuits employing the NUDJFET devices. The other set of simulations compared the NUDJFET and the uniformly doped device as switches in DCTL circuits. Because of its lower turnon voltage the NUDJFET operated at a much lower power supply voltage, while a significant increase in speed was also found. These results indicate that a substantial reduction in power can be obtained by using NUDJFET’s in MESFET circuits.

An Al .5 Ga .5 As gate heterojunction microwave FET

DC, small signal microwave, and large signal switching performance of normally-ON heterojunction Al.5Ga.5As gate, GaAs FETs (N-ON HJFET) with submicron gate dimensions are reported. Ge-doped p-type Al.5Ga.5As and p+-type GaAs layers are grown by liquid phase epitaxy (LPE) on an n-type active channel layer grown by vapor phase epitaxy (VPE). The submicron gate structure is obtained by selectively etching first the GaAs layer and later the Al.5Ga.5As layer. The resulting GaAs overhang is used to self align the source and the drain with respect to the gate. Devices with about 0.6 micron gate length exhibit a maximum available power gain (MAG) of about 9.5 dB at 8 GHz. Large signal pulse measurements indicate an intrinsic propagation delay of 20 psec.