Trap studies in GaInP/GaAs and AlGaAs/GaAs HEMT's by means of low-frequency noise and transconductance dispersion characterizations

The presence of traps in GaInP/GaAs and AlGaAs/GaAs HEMT's was investigated by means of low frequency noise and frequency dispersion measurements. Low frequency noise measurements showed two deep traps (E/sub a1/=0.58 eV, E/sub a2/=0.27 eV) in AlGaAs/GaAs HEMT's. One of them (E/sub a2/) is responsible for the channel current collapse at low temperature. A deep trap (E/sub a1/'=0.52 eV) was observed in GaInP/GaAs HEMT's only at a much higher temperature (/spl sim/350 K). These devices showed a transconductance dispersion of /spl sim/16% at 300 K which reduced to only /spl sim/2% at 200 K. The dispersion characteristics of AlGaAs/GaAs HEMT's were very similar at 300 K (/spl sim/12%) but degraded at 200 K (/spl sim/20%). The low frequency noise and the transconductance dispersion are enhanced at certain temperatures corresponding to trap level crossing by the Fermi-level. The transition frequency of 1/f noise is estimated at 180 MHz for GaInP/GaAs HEMT's and resembles that of AlGaAs/GaAs devices.>