On-state and off-state breakdown in GaInAs/InP composite-channel HEMT's with variable GaInAs channel thickness

Short-channel Ga0.47In0.53As high electron mobility transistors (HEMT's) suffer from low breakdown voltages due to enhanced impact-ionization effects in the narrow band-gap channel. This could limit the application of single-channel devices to medium power millimeter-wave systems. A composite Ga0.47In0.53As/InP channel, which exploits the high electron mobility of Ga0.47In0.53As at low electric fields, and the low impact-ionization and high electron saturation velocity of InP at high electric fields can overcome this limitation. In this paper we study on-state and off-state breakdown of Ga0.47In0.53As/InP composite-channel HEMT's with a variable GaInAs channel thickness of 30, 50, and 100 Angstrom. Reduction of channel thickness leads to the improvement of both on-state and off-state breakdown voltages. In on-state conditions, the enhancement in the effective Ga0.47In0.53As channel bandgap that takes place when the channel thickness is reduced to the order of the de Broglie wavelength (channel quantization) effectively enhances the threshold energy for impact-ionization, which is further reduced by real space transfer of electrons from the Ga0.47In0.53As into the wider bandgap InP, Channel thickness reduction also causes a decrease in the sheet carrier concentration in the extrinsic gate-drain region and therefore, a reduction of the electric field beneath the gate. This, together with the adoption of an Al0.6In0.4As Schottky layer (increasing the gate Schottky barrier height), leads to excellent values of the gate-drain breakdown voltage. In conclusion, composite channel InAlAs/GaInAs/InP HEMT's, thanks to the combined effect of effective band-gap increase, enhanced real space transfer into InP, and sheet carrier density reduction, allow a good trade-off between current driving capability and both on-state and off-state breakdown voltage.