Effect of dislocations on the electrical and optical properties of long-wavelength infrared HgCdTe photovoltaic detectors

Abstract

The quantitative effects of dislocations on the electrical and optical properties of long-wavelength infrared (LWIR) HgCdTe photovoltaic detectors was determined by deliberately introducing dislocations into localized regions of two high-performance arrays having cutoff wavelengths of 9.5 and 10.3 μm at T=78 K. Results show that dislocations can have a dramatic effect on detector R0A product, particularly at temperatures below 78 K. For large dislocation densities, R0A decreases as the square of the dislocation density; the onset of the square dependence occurs at progressively lower dislocation densities as the temperature decreases. A phenomenological model was developed which describes the dependence of the detector R0A product with dislocation density, based on the conductances of individual and interacting dislocations which shunt the p–n junction. Spectral response and quantum efficiency are only weakly affected, as is the diffusion component of the leakage current. The 1/f noise current was found to increase approximately linearly with dislocation density and also tracks with the magnitude of the leakage current similar to a data trendline established for undamaged HgCdTe detectors. These results can be used to understand the performance limitations of LWIR HgCdTe arrays fabricated on heteroepitaxial substrates.

Dislocations as a Noise Source in LWIR HgCdTe Photodiodes

“…25 Finally, we have enhanced our numerical programme in order to take into consideration the influence of dislocations on the effective carrier lifetime as well as the G-R noise (both shot and 1/f). We have verified our numerical approach with measurements of noise current spectra obtained for HgCdTe photodiodes by Johnson et al 13 Fluctuations of the dark current density inside a photodiode caused by the shot noise and the 1/f noise are related to the current noise observed in the electronic system by the energy law. Numerical analysis has allowed us to evaluate the influence of different kinds of noises on the total current noise and find the regions where the noise is mainly generated.…”

“…Figure 3 shows the plot of calculated noise current equal ffiffiffiffiffiffiffiffiffiffi ffi S I Df p at Df ¼ 1 Hz of photodiode presented in Fig. 2 versus the dislocation density at 77 K. Experimental data (points) for LWIR photodiodes (Junction area = 7 Â 10 À6 cm 2 , T = 77 K, bias = À20 mV) are taken after Johnson et al 13 The noise current increases with the dislocation density. Strong linear dependence is observed for dislocation densities above 10 6 cm À2 ; below this value the increase of noise current is weak.…”

“…11 However, one of the main issues in MCT heterostructures are misfit dislocations, which have a strong influence on the decreasing of the detector's performance. 12,13 It is generally known that when the dislocation density does not exceed 10 5 cm À2 , their presence does not considerably influence the performance of the manufactured photoelectric devices including photodiodes. [13][14][15] Such a level of the dislocation density is not usually exceeded in high quality solid materials produced using the bulk grown method, as well as in the layers manufactured by liquid phase epitaxy (LPE).…”

“…12,13 It is generally known that when the dislocation density does not exceed 10 5 cm À2 , their presence does not considerably influence the performance of the manufactured photoelectric devices including photodiodes. [13][14][15] Such a level of the dislocation density is not usually exceeded in high quality solid materials produced using the bulk grown method, as well as in the layers manufactured by liquid phase epitaxy (LPE). However, it can be exceeded in semiconducting heterostructures, so it is reasonable to perform a detailed analysis of the influence of dislocations on the characteristic of devices fabricated from these materials.…”

“…In addition to the fact that dislocations strongly influence G-R rates in devices, they are also sources of the shot noise and 1/f noise. 13,17 The mechanism of the shot noise is well understood, 18 but there are different views on the origin of 1/f noise. Formerly, two current models of 1/f noise were considered in the literature.…”