Analysis of Deviation of Threshold Voltage from Hole Accumulation Model at High Excitation

Abstract

The energy state, concentration, and potential energy for both electrons and holes in the channel of InAlAs/InGaAs high electron mobility transistors (HEMTs) were studied using the theory based on the local density functional method. The numerical result shows that the potential profile changes from the triangle to the square well as the sheet concentration of holes accumulated in the source region ( p s) increases above the sheet concentration of the two-dimensional electron gas (2DEG) because the same amount of electrons as holes was injected from the source to maintain the charge neutrality in the channel. As a result, the quasi-Fermi energy increased and the potential energy of electrons in the channel approached that of the square-well potential, the former led to an increase in the threshold voltage (V TH). The overlap integral between the wavefunctions of an electron and a hole was estimated as a function of the channel thickness (L z ) and was shown to decrease with increasing L z . A detailed theory concerning the relation between the V TH shift and p s was developed and compared with the experimental results. In this theory, the recombination of holes with 2DEG was taken into account, on the assumption that the dominant process was due to the non-radiative Auger recombination mechanism.

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