Enhanced Optical Effect on the Characteristics of MODFET under Back Side Illumination

The DC performance of depletion mode AlGaAs/GaAs MODFET under backside optical illumination is studied. A device structure with fiber inserted into the substrate upto the GaAs layer is considered for direct illumination into the GaAs layer. The AlGaAs layer is considered transparent to illumination. The photoconductive effect and the internal reflection effect which increase the 2DEG channel electron concentration are considered. These free electrons generated in the GaAs layer due to both photoconductive effect and the internal reflection effect are collected in 2DEG, there by increasing the source to drain current. The photo generated holes in GaAs layer drift towards the semi-insulating substrate and are capacitively coupled into the grounded source. The sheet concentration , I-V characteristics, transconductance and transfer characteristics of the device AlGaAs/GaAs MODFET have been evaluated and discussed. The I-V characteristics is compared with available experimental data at a particular gate source voltage with and without illumination.