High transconductance InGaAs FETs using an undoped amorphous silicon Schottky barrier enhancement layer

High-transconductance Pt/a-Si:H-gate In/sub 0.53/Ga/sub 0.47/As FETs have been fabricated using an MOCVD grown n-InGaAs channel layer and a thin layer of PECVD hydrogenated amorphous silicon (a-Si:H) to enhance the Schottky barrier height of the metal contact. The reverse characteristic of the Schottky diode is characterized by an early soft breakdown, and the leakage current is relatively high at a few mA (V/sub gs/=-2 V) for a 1.5- mu m*100- mu m-gate device, although this is probably caused by the a-Si:H layer being too thin (100 AA). Similar devices fabricated using a 900-AA-thick layer yield a leakage current of about 5 nA for equivalent devices and bias conditions. The best MESFET devices exhibit a transconductance of 218 mS/mm at V/sub gs/=0 V and a peak transconductance of up to 249 mS/mm. The devices have a threshold voltage of around -3.5 V.<
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