DIFFUSION LENGTHS OF CARRIERS IN N-TYPE AND P-TYPE ZNMGSSE CLADDING LAYERS OF GREEN LASER-DIODES

We have used cross sectional cathodoluminescence microscopy as a fast and nondestructive tool to characterize II-VI based green laser diodes . We find evidence for carrier mediated excitation of semiconductor la yers that are not directly irradiated by the focused electron beam, fr om which diffusion lengths of lower mobility carriers (presumably hole s) can be estimated. We find that N-doped (p-type) ZnMgSSe exhibits a very low (near) band edge luminescence efficiency. The diffusion lengt h of minority carriers in p-type ZnMgSSe:N [(1- 2) x 10(17) cm(-3) net acceptor concentration] was found to be lower than for n-type ZnMgSSe :Cl with roughly equal dopant concentration. The diffusion length of m inority carriers in n-type ZnMgSSe:Cl decreases from 0.21 mu m for a d oping level of (1-2) x 10(17) cm(-3) to <0.05 mu m when the n- type do ping is increased to (2-4) x 10(18) cm(-3). This decrease in diffusion length is accompanied by an increase of a broad luminescence band aro und 550 nm, which is attributed to Cl-related defects in the gap. The effective probe size in our cross sectional CL is close to the waist d iameter of the focused electron beam. This phenomenon is discussed wit h regard to the sample geometry and its implication for the determinat ion of carrier diffusion lengths. (C) 1998 American Institute of Physi cs. [S0021-8979(98)02614-0].