INFLUENCE OF THE DELTA DOPING POSITION IN THE CHANNEL ON THE DEVICE PERFORMANCE OF ALGAAS INGAAS MODULATION-DOPED FIELD-EFFECT TRANSISTORS

We present an experimental and theoretical investigation of the influence of delta doping in the InGaAs channel on the device performance of Al0.25Ga0.75As/In0.2Ga0.8As/GaAs pseudomorphic modulation-doped field-effect transistors (MODFETs). Self-consistent calculations of the band structure were used to determine the optimum spike position to introduce the doping into the channel. The results of our calculations lead to a new device approach, the backside pulse-doped channel MODFET. The device uses a narrow doping pulse at the backside interface of the InGaAs layer. For this kind of layer structure, the calculations predict that the interaction between electrons and donors and thereby the transport properties of the electrons in the channel can be modulated with applied gate voltage. At positive gate voltage the device operates in the conventional high electron mobility transistor mode, whereas at lower voltages a metal-semiconductor field-effect transistor-like behavior is observed. This has been experimentally confirmed for devices with a 2-nm-wide doping pulse located at the backside interface of the InGaAs/GaAs layers. For these devices with 0.35-mu-m gate length we measured a maximum saturation current as high as 800 mA/mm with a transconductance of 430 mS/mm.