Investigation of minority carrier diffusion length in shallow junctions by angle-resolved illumination technique

In this paper, we discuss a new approach to the determination of minority carrier diffusion length (Ld) on flat top surface shallow junction devices in which photocurrent is dominated by diffusion component as in solar cells. In our method, we propose the use of a single monochromatic light beam of appropriate wavelength, incident on the device surface at various angles. Under such experimental conditions, the short circuit current of the device is expressed as a function of the internal spectral response and device reflectance. Then diffusion length can be simply derived by the analysis of the experimental ratio between photocurrent measured at various incidence angles and when light impinges the device orthogonally, as function of the incident angle. An analytical model is proposed based on the modified absorption coefficient as a function of refractive angle and an experimental set-up for the evaluation of minority carrier diffusion length is proposed.