Correlation of laser-beam-induced current with current-voltage measurements in HgCdTe photodiodes

Abstract

Laser-beam-induced current (LBIC) is being investigated as an alternative to electrical measurements of individual photodiodes in a two-dimensional array. This is possible because LBIC only requires two electrical contacts to an array and the two-dimensional scanning of a focused laser beam across the array to image the entire array. The measured LBIC profiles, obtained from linear arrays of HgCdTe photodiodes, will be used to study the uniformity of photodiodes in the array and to extract the R 0 A of the photodiodes. It will be shown that the shape of the LBIC signal is correlated to the electrical performance of the photodiode, with R 0 A related to the spreading length of the photodiodes. Linear arrays of n-on-p, mid-wavelength infrared (MWIR) and long wavelength infrared (LWIR) devices were formed in liquid-phase epitaxy HgCdTe epilayers using a plasma junction-formation technique. The LBIC profiles were measured on each of the devices at various temperatures. For the MWIR devices, the extracted spreading length shows no correlation with R 0 A. However, the LBIC signal does detect nonuniform devices within the array. For the case of the LWIR devices, the spreading length is extracted as a function of temperature, with the R 0 A subsequently calculated from the spreading length. The calculated R 0 A, obtained without requiring contact to each photodiode in the array, agrees well with electrical measurements. Asymmetry of the LBIC signals for certain devices in the arrays is shown to be a result of localized leakage at the photodiode junction or from the contact pads through the passivation layers. These results are confirmed by numerical modeling of the device structures.

Recent Advances in Floating Photovoltaic Systems

“…Therefore, the photo‐induced current which is proportional to the solar cell diffusion length can be measured and analyzed [96] . The test results in a map of the solar cell performance distribution that helps in determining several types of defects in the solar cell's material [79,96,97] I–V characteristics curve can be also employed to detect solar cell defects [98] .…”

Laser beam induced current for qualitative evaluation of HgCdTe van der Pauw sample uniformity

“…These contacts are typically placed on either side of the wafer area that is under investigation. In contrast, if the photogenerated carriers are able to diffuse to and be separated by a built-in electric field, a current will be measured in the external circuit [11]. This lateral photoeffect was so named since it occurs parallel to the plane of the junction.…”

“…The previously published research efforts to develop LBIC for quantitative photodiode characterisation of arrays of n-on-p junction MWIR HgCdTe photodiodes were based on a measurement configuration with remote contacts to the p-type bulk [11]. In this case, remote means more than approximately 20 diffusion lengths from the junction edge, which was previously proposed as a sufficient distance to eliminate this variable from the analysis [9].…”

“…The measurement configurations for this case are shown in Figure 2 for different cases of illumination position, along with the typical LBIC profiles expected from these measurements. The features of the LBIC line profiles through the junctions that were of special interest are the peak-to-peak magnitude, decay of the curve away from these peaks, and the symmetry of the profiles [9,11].…”

Polarity inversion and coupling of laser beam induced current in As-doped long-wavelength HgCdTe infrared detector pixel arrays: Experiment and simulation

“…The temperature and laser beam property dependence of LBIC imaging on mid-wavelength Hg-vacancy doped HgCdTe p-n junctions has been described by Redfern, who illustrated the peak-to-peak LBIC signal would reach saturation under low temperature and high laser beam intensity conditions. 18,19 However, in As-doped HgCdTe, the arsenic may reside on either the metallic sublattice thus behaving as a donor or the nonmetallic sublattice thus acting as an acceptor. 20 Specifically, when used on a long wavelength HgCdTe infrared detector, As-doped p-type HgCdTe is very sensitive to temperature.…”