Effect of Junction Depth on the Parameters of GaAs Shallow-Homojunction Solar Cells

A diagnostic study of the photovoltaic parameters of the GaAs shallow-homojunction solar cell has been carried out. Two types of n** plus /p/p** plus cells, 'deep' and 'shallow', were fabricated for the study. The former used as-grown MOCVD structures with n** plus layer thickness ranging from 750 to 14,500 angstrom; for the latter, a device with a 600-angstrom n** plus layer was thinned down to failure by successive chemical etching. The deep devices exhibited an approximately exponential decrease of J//s //c over the whole range of junction depth. The light-dependent parameters of the shallow cells exhibited maxima at slightly different n** plus thicknesses. The maximum in efficiency occurred at 400 angstrom. Computer modeling was able to predict the dependence of J//s //c on junction depth for both shallow and deep cells. This dependence was different in the two cases because the material properties of the two sets of devices were different.