Interpretation of transconductance dispersion in AlGaAs/InGaAs pseudomorphic high electron mobility transistor by capacitance deep level transient spectroscopy

The transconductance dispersion in AlGaAs/InGaAs PHEMT grown by MBE was int erpreted by means of capacitance DLTS technique. When the gate bias was -0. 2 V, the transconductance decreased at a very broad frequency range of 5.5 Hz -1.7x10(4) Hz. However, when a positive bias was applied to the gate, th e transconductance increased at a lour frequency range and then decreased a t a high frequency range. In the transconductance dispersion measurement as a function of temperature, the transition frequency shifted to higher freq uency region with the increase in temperature. The emission energy for the change in the transition frequency was determined to be 0.394 eV from the t emperature dependency of the transition frequency. In the capacitance DLTS measurements, we observed DX-center with thermal activation energy of 0.420 eV and two hole trap-like signals. The DX-center peak decreased as the fil ling pulse decreased from +0.6 V and disappeared at the bias of -0.1 V. Com paring the activation energy of DX-center in DLTS measurement with that obt ained from the positive transconductance dispersion, we found that the DX-c enter led to the positive transconductance dispersion in the device.