1/f noise in Hg 1-x Cd x Te detectors

Abstract

This paper investigates 1/f noise performance of Hg<SUB>1-x</SUB>Cd<SUB>x</SUB>Te photovoltaic detectors when detector current is varied by changing detector area, bias, temperature and incident flux. Holding detector bias and temperature constant, measured 1/f noise current is proportional to the detector current. However for all detector areas measured, non-uniformity is observed in the noise current due to the varied quality of the detectors. Even for the &#955;<SUB>c</SUB>=16&#956;m , 4-&#956;m-radius, diffusion-limited detectors at 78K held at reverse bias, the average and standard deviation in dark current is I<SUB>d</SUB>=9.76+/- 1.59x10<SUP>-8</SUP>A while the average and standard deviation in noise current at 1 Hz in a 1 Hz bandwidth is i<SUB>n</SUB>=1.01+/- 0.63x10<SUP>-12</SUP>A. For all detector areas measured at 100 mV reverse bias, the average and standard deviation in dark current to noise current ratio is &#945; <SUB>D</SUB>=i<SUB>n</SUB>/I<SUB>d</SUB>=1.39+/- 1.09x10<SUP>-5</SUP>. Defects are presumed resident in the detectors that produce greater non- uniformity in the 1/f noise as compared to the dark current at 100 mV reverse bias. Noise was also measured as a function of temperature for two &#955; <SUB>c</SUB>=16 micrometers detectors from 55 K to 100 K. The average and standard deviation in the noise current to dark current ratio is &#945;<SUB>D</SUB>=i<SUB>n</SUB>/I<SUB>d</SUB>=2.36+/- 0.83x10<SUP>-5</SUP> for the 26-micrometers -diameter detector and (alpha) <SUB>D</SUB>=1.71+/- 0.69x10<SUP>-5</SUP> for the 16-micrometers -diameter detector. Dark and noise current were measured while changing the bias applied to a detector. In the diffusion-limited portion of the detector I-V curve, 1/f noise is independent of bias with &#945; <SUB>D</SUB>=i<SUB>n</SUB>/I<SUB>d</SUB>=1.51+/- 0.12x10<SUP>-5</SUP>. When tunneling currents dominated, &alpha;<SUB>T</SUB>=i<SUB>n</SUB>/I<SUB>d</SUB>=5.21+/- 0.83x10<SUP>-5</SUP>. The 1/f noise associated with tunneling currents is a factor of three greater than the 1/f noise associated with diffusion currents. In addition, 1/f noise was measured on detectors held at -100 mV and 78 K under dark and illuminated conditions. The average noise to current ratio &alpha;<SUB>D</SUB> was approximately 1.5 x 10<SUP>-5</SUP> for dark and photon-induced diffusion current. However, detector-to-detector variations exist even within a single chip. The two most important points are that non-uniformities in material/fabrication need to be addressed and that each individual type of current component has an associated 1/f noise current component, the magnitude of the relationship being different depending on the source current.