Latest Developments in Long-Wavelength and Very-Long-Wavelength Infrared Detection with p-on-n HgCdTe

Abstract

We report recent developments at Commissariat à l'Energie AtomiqueLaboratoire d'Electronique des Technologies de l'Information Infrared Laboratory on the processing and characterization of p-on-n HgCdTe (MCT) planar infrared focal plane arrays (FPAs) operating in the long-wavelength infrared (LWIR) and very-long-wavelength infrared (VLWIR) spectral bands. The active layers in these FPAs were grown by liquid phase epitaxy (LPE) on a latticematched CdZnTe substrate. This technological process results in lower dark current and lower serial resistance than for n-on-p vacancy-doped architecture and thus is better adapted for lower flux detection or higher operating temperature. This architecture was evaluated for space applications in the LWIR and VLWIR spectral bands with cutoff wavelengths from 10 to 17 lm at 78 K. Innovations have been introduced to the technological process to form a heterojunction by use of an LPE growth technique. The initial objective was to reduce the dark current at low temperatures, by reducing the transition temperature from diffusion-limited to depletion-limited dark current. Another advantage is that the wider bandgap obtained in the vicinity of the junction ensures less sensitivity to the defects present at the interface between MCT and passivation layers. Electrooptical characterization of p-on-n photodiodes was performed on quarter video graphics array format FPAs with 25 and 30 lm pixel pitches. The results revealed excellent operabilities in current and responsivity, with low dispersion, and noise limited by current shot noise. Studies performed on the dark current show that dark current densities at 78 K are consistent with the heuristic prediction law ''Rule 07''. Below this temperature, dark current varies as a pure diffusion current for a variety of devices from different manufacturers, introducing a temperature range limitation in the description of the ''Rule 07'' law.

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

“…Note moreover that such a behavior deviates from rule07. Indeed, as we previously mentioned [ 18 ] in the case of LWIR-VLWIR diodes cooled down below 80-50K, measured dark current is always higher than rule07 whatever the technology or the growth process so that rule07 might not be used to estimate dark current in this temperature range. This has been also observed on data from other HgCdTe FPA suppliers.…”

Diffusion of Dopants and Components in Arsenic-Implanted CdTe/HgCdTe Structures under Different High-Temperature Annealing Conditions

“…A critical path to improve the device performance of MCT-based photodiodes is to suppress dark current. Therefore, on one hand, the p-on-n photodiode structure is adopted to reduce bulk dark current [1,2]; on the other hand, the high-quality passivation of MCT surface is required to reduce the surface leakage and recombination current.…”

“…The arsenic ion implantation and the post-annealing have been demonstrated to be a feasible roadmap to achieve the p-on-n structure [2]. Accordingly, the dislocations and defects at the interface between the passivation layer and the MCT epilayer originating from lattice mismatch have to be healed or reduced to acquire a good surface passivation.…”

Characterization and Simulation of p-Type Ion Implantation in MCT

“…With decades of development, the n-on-p device has provided excellent performance [7]. However, for the infrared detection application of low dark current and low flux in long wavelength infrared (LWIR) and very long wavelength infrared (VLWIR) regions, the p-on-n device has been demonstrated to possess better performances [8][9][10] such as low dark current, low series resistance, and high operating temperature. For II-VI materials such as MCT, group V elements, especially arsenic, can serve as p-type dopants.…”