Schottky barriers and ohmic contacts on n-type InP based compound semiconductors for microwave FET's

InP, and In
0.73
Ga
0.27
As
0.6
P
0.4
, and In
0.53
Ga
0.47
As lattice matched to InP are of special importance as active FET channel materials because of the high electron velocity and/or high electron mobility they offer. Using a AuGe/Ni/Au metallization system, specific contact resistances of 5 × 10
^-7
Ω . cm
²
, 8 × 10
^-7
Ω . cm
²
, and 5.8 × 10
^-6
Ω cm
²
were obtained for ohmic contacts on In
0.53
Ga
0.47
As, InP, and In
0.89
Ga
0.11
As
0.24
P
0.76
, respectively. Leakage currents of 10 µA at 7-V reverse bias were observed for 1 × 200-µm gates on InP. and In
0.89
Ga
0.11
As
0.24
P
0.76
FET's having a SiO
2
film about 50 Å thick under the gate. A thin SiO
2
layer underneath the gate improved the Schottky-gate I-V characteristics, but thick oxides severely degraded the microwave performance of the FET's. These excellent ohmic contacts and Schottky barriers resulted in a maximum insertion gain of 15 dB at 8 GHz and a noise figure of 2.5 dB with 8-dB gain at 7 GHz for the InP deviees. For 1.15-eV In
x
Ga
1-x
As
y
P
1-y
FET's, the resulting gain was 9 dB at 8 GHz.