Low-dark current p-on-n MCT detector in long and very long-wavelength infrared

Abstract

This paper presents recent developments done at CEA-LETI Infrared Laboratory on processing and characterization of p-on-n HgCdTe (MCT) planar infrared focal plane arrays (FPAs) in LWIR and VLWIR spectral bands. These FPAs have been grown using liquid phase epitaxy (LPE) on a lattice matched CdZnTe substrate. This technology presents lower dark current and lower serial resistance in comparison with n-on-p vacancy doped architecture and is well adapted for low flux detection or high operating temperature. This architecture has been evaluated for space applications in LWIR and VLWIR spectral bands with cutoff wavelengths from 10µm up to 17µm at 78K. Innovations have been introduced to the technological process to form a heterojunction with a LPE growth technique. The aim was to lower dark current at low temperature, by decreasing currents from the depletion region. Electro-optical characterizations on p-on-n photodiodes have been performed on QVGA format FPAs with 30µm pixel pitches. Results show excellent operabilities in current and responsivity, with low dispersion and noise limited by current shotnoise. Studies performed on dark current show that dark current densities are consistent with the heuristic prediction law "Rule07" at 78K. Below this temperature, dark current varies as a pure diffusion current.

Advances of Sensitive Infrared Detectors with HgTe Colloidal Quantum Dots

“…Nowadays, thermal imaging relies primarily on bulk epitaxial semiconductor materials. In mid-wave infrared (MWIR, 3-5 µm) and long-wave infrared (LWIR, 8-12 µm), it is dominated by narrow bandgap semiconductor material such as InSb [18], HgCgTe [19,20], quantum-wells [21] and type-II superlattices [22,23]. However, these materials were typically prepared by molecular beam epitaxy or chemical vapor deposition, which leads to high fabrication and processing costs.…”

LWIR quantum efficiency measurements using a calibrated MCT photodiode read by a cryo-HEMT-based amplifier

“…This phenomenon has been already observed on p-on-n architecture. 6 This is due to the fact that the diffusion length (capability to the electronic charge to diffuse into HgCdTe material) decreases strongly at low temperature. The consequence of this is a decrease of the fill factor of the photodiode and so a decrease of the photoresponse.…”

HgCdTe detectors for space and science imaging in France: general issues and latest achievements

“…Very recently in 2015, several points have been added to this curve (represented by four colored diamond symbols in Figure 9) for extremely long cutoff wavelength (between 15.5µm and up to 17.3µm at 78K). The mid response cutoffs measured on such diodes perfectly follows the expected Hansen's law [ 14 ] down to 50K, giving values ranging from 17.5µm up to 19.7µm at 50K, with a classical wideband uniform spectral QE, from MWIR to LWIR and VLWIR [ 17 ], corresponding to cadmium composition below 0.2 (0.1957 to 01917).…”

“…Using a given a given set of geometries (diodes with diameter ranging between 120µm to 10µm), the general principle is to search a lateral collection length consistent with a photonic current density independent on the diode diameter. This method is in fact an efficient way to estimate this diffusion length Ld at different temperatures [ 15 ]. Figure 8 shows the evolution of the estimated Ld as function of the temperature.…”