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) su ffer 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 Ga0.47 In0.53As/InP channel, which exploits the high electron mobility of Ga0.47In 0.53As at low electric fields, and the low impact-ionization and high elect ron saturation velocity of InP at high electric fields can overcome this li mitation. In this paper we study on-state and off-state breakdown of Ga0.47 In0.53As/InP composite-channel HEMT's with a variable GaInAs channel thickn ess of 30, 50, and 100 Angstrom. Reduction of channel thickness leads to th e improvement of both on-state and off-state breakdown voltages. In on-stat e conditions, the enhancement in the effective Ga0.47In0.53As channel bandg ap that takes place when the channel thickness is reduced to the order of t he de Broglie wavelength (channel quantization) effectively enhances the th reshold energy for impact-ionization, which is further reduced by real spac e transfer of electrons from the Ga0.47In0.53As into the wider bandgap InP, Channel thickness reduction also causes a decrease in the sheet carrier co ncentration in the extrinsic gate-drain region and therefore, a reduction o f the electric held beneath the gate. This, together with the adoption of a n Al0.6In0.4As Schottky layer (increasing the gate Schottky barrier height) , leads to excellent values of the gate-drain breakdown voltage. In conclus ion, composite channel InAlAs/GaInAs/InP HEMT's, thanks to the combined eff ect 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.