Dr. Greenberg et al., IMPACT IONIZATION AND TRANSPORT IN THE INALAS N(+)-INP HFET/, I.E.E.E. transactions on electron devices, 42(9), 1995, pp. 1574-1582
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.