Degradation effects and stabilization of InAlAs/InGaAs-HFETs

In recent years the development of InAlAs/InGaAs-HFETs has advanced considerably, enabling maximum transconductances and cut-off frequencies to be realized. The HFET is therefore a highly attractive component for use in integrated circuits, e.g. low-noise amplifiers for satellite communication. For industrial use the reliability of the integrated circuit is of vital importance, but depends to a large extent on the reliability of the HFET. This aspect has hardly been discussed in the open HFET literature during the last years, or has only been partially realized. The available literature attributes the degradation of the HFET to the instability of the ohmic contacts, or to a change in the sheet concentration. In the work presented here, the degradation of the InAlAs/InGaAs-HFET is thoroughly examined for the first time and the free InAlAs-surface has been clearly established as the location of the degradation.