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-Induced-Current (LBIC) imaging has proven useful in qualitatively assessing electrically active defects and localized non-uniformities in HgCdTe materials and devices used for infrared photovoltaic arrays. To further the development of a quantitative working model for LBIC, this paper focuses on the application of the technique to photovoltaic structures that are represented by a discrete element equivalent circuit. For this particular case the LBIC signal arises due to the lateral photovoltaic 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 model indicates that the LBIC signal has an extremely weak dependence on the p-n junction reverse saturation current, and shows a linear dependence with laser power. This latter feature map be useful for non-contact measurement of the quantum efficiency of individual photodiodes within 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 same form as the roll-off in the short circuit photoresponse and, therefore, can be used to extract the diffusion length of minority carriers. Experimental data is obtained from an arsenic implanted p-on-n junction fabricated on MBE grown Hg_1-xCd_xTe material with an x-value of 0.3. The p-on-n diode is shown to be uniform and of high quality with an R₀A product of 1×10⁸ Ω·cm² at 77 K. The validity of the simple model developed in this paper, is confirmed by the excellent agreement with experimental results. Consequently, the LBIC technique is shown to be an appropriate diagnostic tool for non-contact quantitative analysis of semiconductor materials and devices.