Low-frequency transconductance dispersion in InAlAs/InGaAs/InP HEMT's with single- and double-recessed gate structures

The effects of trapping mechanisms on the transconductance of single- and double-recessed InAlAs/InGaAs/InP HEMT's are examined. Measurements at room temperature indicate transconductance dispersion occurring primarily between 100 Hz and 1 MHz. A detailed examination of the dispersion yields two mechanisms with different activation energies which were determined by measuring the transition frequencies as functions of temperature. One mechanism, causing negative dispersion, has an activation energy of 0.17 eV and was found only in the double-recessed structure. The other mechanism, causing positive dispersion and common to both structures, has a dominant transition with an activation energy of 0.51 eV at low fields. The first mechanism appears to be associated with surface states, while the second is caused by electron traps in the InAlAs or its interface with the InGaAs channel. Transient response measurements were also used to examine the location of the traps and to study the field dependence of the characteristic times.