Dislocations as a Noise Source in LWIR HgCdTe Photodiodes

Abstract

The effect of dislocation on the 1/f noise current in long-wavelength infrared (LWIR) reverse biased HgCdTe photodiodes working at liquid nitrogen (LN) temperature was analyzed theoretically by using a phenomenological model of dislocations as an additional Shockley-Read-Hall (SRH) generation-recombination (G-R) channel in heterostructure. Numerical analysis was involved to solve the set of transport equations in order to find a steady state values of physical parameters of the heterostructure. Next, the set of transport equations for fluctuations (TEFF) was formulated and solved to obtain the spectral densities (SD) of the fluctuations of electrical potential, quasi-Fermi levels, and temperature. The SD of mobility fluctuations, shot G-R noise, and thermal noise were also taken into account in TEFF. Additional expressions for SD of 1/f fluctuations of the G-R processes were derived. Numerical values of the SD of noise current were compared with the experimental results of Johnson et al. Theoretical analysis has shown that the dislocations increase the G-R processes and this way cause the growth of G-R dark current. Despite the fact that dislocations increase both shot G-R noise and 1/f G-R noise, the main cause of 1/f current noise in LN cooled LWIR photodiodes are fluctuations of the carriers mobility determined by 1/f fluctuations of relaxation times. As the noise current is proportional to the total diode current, growth of G-R dark current caused by dislocations leads to the growth of noise current.

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“…Similarly as in Ref. 21, we have determined Auger 1 and Auger 7 as well as SHR generation rates caused by metal vacancies and dislocations. BTB and TAT were also included.…”

“…We have adopted their results for HgCdTe in some previous works. [19][20][21]26 Handel's theory of 1/f noise is based on the fact that, in accordance with the quantum electromagnetic field theory, electric charge carriers are accompanied by photons. Interactions leading to the change in carrier velocity are sources of creation or annihilation of photons (Bremsstrahlung).…”

“…In our previous paper, Ref. 21, we have determined the Hooge coefficients 30 for 1/f noise caused by Auger 1, Auger 7, radiative and SHR G-R mechanisms. The influence of dislocations on 1/f noise was also determined.…”

“…Similarly to Ref. 21, the dislocations' influence on noise current was also taken into account in this paper. By solving TEFF, we can determine the spatial distribution of the temperature fluctuations, electrical potential fluctuations and quasi-Fermi energies fluctuations for electron and holes for an arbitrarily chosen frequency in a Df ¼ 1 Hz frequency range.…”

“…We have also analyzed for some years [19][20][21] fluctuation phenomena by using our Langevin-like numerical method developed by Jóźwikowski, and now it enables the determining of the noise current spectrum in heterostructures. In addition, we also determined distributions of noise power density caused by fluctuations of Joule power.…”