A mathematical model of the induced junction MOS structure has been developed and used to study the behaviour of the device under monochromatic illumination. Dependence of surface photovoltage on doping level, oxide charge, carrier lifetime, illumination intensity and absorption coefficient has been investigated. The model has been used to calculate the upper bound on the open circuit voltage of the structure when used as the active region of the induced junction solar cell. Effects of traps on the surface photovoltage and the open circuit voltage have also been investigated. The model has also been found useful in evaluating the SPV method of minority carrier diffusion length measurement.
The front contact to the induced junction cell is through MIS Schottky barrier diodes. Characteristics of such diodes have been studied to find the conditions for their efficient operation as the contact to the cell. The behaviour of the complete cell under solar illumination (AMI) has been investigated. The two-dimensional current flow effect in the cell has been accounted for by a distributed source-resistance model. The complete I-V characteristic of the cell has been obtained in three parts: (a) 'ideal' characteristics pertaining to the active region of the cell, (b) 'internal' characteristics including the effect of the current flow in the sheet resistance of the inversion layer and (c) 'external' characteristics including the front contact and the effects in (a) and (b). With a fixed oxide charge of 5x1011 cm-2 , a maximum efficiency of about 15% is calculated. A grid spacing of about 150 µm is indicated for an inversion layer sheet resistance of 40 kΩ/sq.
For the fabrication and testing of the induced junction cells, the laboratory has been equipped with the necessary facilities over a period of time. The fabrication work has mainly been centered around thermal SiO2 cells. Cells with an efficiency of about 10% have been fabricated. Evaporated SiO cells with efficiencies in the range of 13% (active area) have been produced. These cells are easier to fabricate than the thermal oxide cells and a maximum temperature of only 450°C is involved. Anodic oxide cells have also been tried and a maximum efficiency of 8.4% has been obtained.