Design, processing and characterization of delta-doped channel AlGaAs/InGaAs/GaAs HFETs

We report on design, processing and characterization of AlGaAs/InGaAs/GaAs HFETs which feature the power capabilities of double delta-doped devices and the low noise performance of the standard HFETs. To study the influence of delta doping position on the subband energies and sheet charge density, numerical simulations based on a self-consistent solution of Poisson's and Schrödinger's equations have been used for different channel thicknesses. Three different devices with a single δ-doped layer located at three different positions inside the channel have been fabricated and tested. On-wafer noise measurements have revealed that the position of the delta-doped layer can be optimized to minimize the noise figure without any relevant degradation of the maximum transconductance. The device with the delta-doped layer closer to the bottom heterointerface was found to exhibit the best performance in terms of the maximum cutoff and maximum oscillation frequencies and the minimum noise figure.