OFF-STATE BREAKDOWN IN INALAS/INGAAS MODFETS

Recent efforts are being focussed on improving the breakdown voltage (BV) of InAlAs/InGaAs MODFET's on InP 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 InAlAs/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 Delta E(C) between insulator and channel, they enter the channel hot, into the high-held 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.