IMPACT IONIZATION AND TRANSPORT IN THE INALAS N(+)-INP HFET/

We have carried out an experimental study exploring both impact ioniza tion and electron transport in InAlAs/n(+)-InP HFET''s. Our devices sh ow no signature of impact ionization in the gate current, which remain s below 17 mu A/mm under typical bias conditions for L(g) = 0.8 mu m d evices (60 times lower than for InAlAs/ZnGaAs HEMT's). The lack of imp act ionization results in a drain-source breakdown voltage (BVDS) that increases as the device is turned on, displaying an off-state value o f 10 V. Additionally, we find that the channel electron velocity appro aches the InP saturation velocity of about 10(7) cm/s (in devices with L(g) < 1.6 mu m) rather than reaching the material's peak veloity. We attribute this to the impact of channel doping both on the steady-sta te peak velocity and on the conditions necessary for velocity overshoo t to take place. Our findings suggest that the InP-channel HFET benefi ts from channel electrons which remain cold even at large V-GS and V-D S making the device well-suited to power applications demanding small I-G, low g(d), and high BVDS.