VARIABLE-AREA DIODE DATA-ANALYSIS OF SURFACE AND BULK EFFECTS IN MWIRHGCDTE CDTE SAPPHIRE PHOTODETECTORS

This study investigates the separate dark current components which are dominant in the diffusion-limited regime in MWIR n/p HgCdTe/CdTe/sapp hire photodetectors. Both mesa and planar configurations of variable-a rea diodes were fabricated and evaluated over the temperature range fr om 78 to 250 K. Simple analytical expressions are used to calculate th e contributions of bulk, lateral and surface effects from the perimete r/area dependence of R0A and measurement of the minority carrier diffu sion length. The analysis indicates that at 180 K the mesa diode resul ts can be accounted for by bulk and lateral currents, but that the pla nar diodes are limited by surface currents. The 180 K median R0A for t he mesa diodes ranges from 63 OMEGA cm2 for 500 x 500 mum2 diode areas to 14 OMEGA cm2 for 30 x 30 mum2 diodes at a cut-off wavelength of 4. 64 mum. Scanning laser microscope measurements determine the 180 K ele ctron minority carrier diffusion length to be 17-18 mum.