NOISE (1/F) AND DARK CURRENTS IN MIDWAVELENGTH INFRARED PACE-I HGCDTE PHOTODIODES

A detailed and systematic study of excess (1/f) noise currents and their associated dark currents in midwavelength infrared HgCdTe/CdTe/sapphire (PACE-I) n+/p photodiodes is presented. Variable area diodes ranging in size from 9.0 X 10(-6) to 2.5 X 10(-3) cm2 were examined to determine bulk and surface contributions. Variable temperature measurements ranging from 77 to 250 K were performed to isolate limiting current and noise mechanisms. Two temperature regions, 115-120 and 180-200 K, are emphasized. Both bare surface diodes with only a thin native oxide at the surface and electron-beam deposited CdTe passivated diodes were studied. The measured diodes exhibited high performance with R0A products > 10(5) OMEGA cm2 at 120 K for 4.5-mu-m cutoff wavelength. Data from a large number of devices are reported. Experimental data at diffusion-current-limited temperatures do not support a proportionality between the noise and dark currents. For these temperatures, the dependence of noise current on temperature yields an activation energy of 0.75E(g) which does not support generation-recombination centers located in the midgap. At low temperatures, the analysis of data is complex because of a large scatter in data indicating influence of localized defects. The differences between present results and theoretical model calculations of Kleinpenning are addressed.