Off-State Breakdown in InA1As/InGaAs MODFET's

摘要

Recent efforts are being focussed on improving the breakdown voltage (BV) ofInA1As/lnGaAs MODFET's on lnP towards high power applications. A detailed understanding of the physics of breakdown in these devices is still lacking. In this work, we carry out a study of off state breakdown on state of the art MODFET's in this material system. Through a combination of a surface depleted cap and mesa sidewall isolation the devices have BV 's of around 10 V. We find that BV shows a negative temperature coefficient and also decreases with a higher InAs mole fraction in the channel. As we have recently found in InA1As/n(+)-InGaAs HFET's, off state breakdown appears to be a two step process. First, electrons are emitted by thermionic field emission from the gate to the insulator. Second, as a consequence of the large electric field in the insulator and the substantial AE( between insulator and channel),they enter the channel hot, into the high field drain gate region, and relax their energy through impact ionization. This combined hypothesis is able to explain why the MODFET breakdown voltage depends on both channel and insulator design parameters.