A DISCRETE ELEMENT MODEL OF LASER-BEAM INDUCED CURRENT (LBIC) DUE TO THE LATERAL PHOTOVOLTAIC EFFECT IN OPEN-CIRCUIT HGCDTE PHOTODIODES

The non-destructive optical characterization technique of Laser-Beam-I nduced-Current (LBIC) imaging has proven useful in qualitatively asses sing electrically active defects and localized non-uniformities in HgC dTe materials and devices used for infrared photovoltaic arrays, To fu rther the development of a quantitative working model for LBIC, this p aper focuses on the application of the technique to photovoltaic struc tures that are represented by a discrete element equivalent circuit. F or this particular case the LBIC signal arises due to the lateral phot ovoltaic effect in non-uniformly illuminated open-circuit photodiodes. The outcomes of the model predict all of the experimentally observed geometrical features of the LBIC image and signal, Furthermore, the mo del indicates that the LBIC signal has an extremely weak dependence on the p-n junction reverse saturation current, and shows a linear depen dence with laser power, This latter feature may be useful for non-cont act measurement of the quantum efficiency of individual photodiodes wi thin a large two-dimensional focal plane array, The decay of the LBIC signal outside the physical boundary of the p-n junction is of the sam e form as the roll-off in the short circuit photoresponse and, therefo re, can be used to extract the diffusion length of minority carriers, Experimental data is obtained from an arsenic implanted p-on-n junctio n fabricated on MBE grown Hg1-xCdxTe material with an x-value of 0.3. The p-on-n diode is shown to be uniform and of high quality with an R( o)A product of 1 x 10(8) Omega . cm(2) at 77 K. The validity of the si mple model developed in this paper, is confirmed by the excellent agre ement with experimental results, Consequently, the LBIC technique is s hown to be an appropriate diagnostic tool for non-contact quantitative analysis of semiconductor materials and devices.