HgCdTe FPAs made by Arsenic-ion implantation
2008
In this paper, we report the fabrication and electro-optical characterization of both long-wavelength (LWIR) and middle-wavelength
(MWIR) p-on-n infrared photodiodes in HgCdTe. LWIR and MWIR HgCdTe epitaxial layers were grown
by liquid phase and molecular beam epitaxy respectively. p-type doping was obtained by arsenic implantation and n-type
doping by indium incorporation during growth.
The arsenic concentration profile determined by Secondary Ion Mass Spectroscopy showed multi-component diffusion
after Hg post-implant annealing. The process yields an arsenic activation efficiency of around 50%, estimated from
MEMSA (Maximum Entropy Mobility Spectrum Analysis) measurements. The damage induced by arsenic implantation
into HgCdTe have been examined by transmission electron microscopy (TEM) and suggest the formation of an array of
dislocations loops after arsenic implantation. However, after annealing under Hg overpressure, the impact of
implantation falls below the sensitivity of the TEM, suggesting that annealing effectively suppresses most of the defects.
The p-on-n photodiodes showed low leakage currents (shunt resistance>100 MOhms) and typical RoA values
comparable to the state of the art (RoA>4000 Ω.cm 2 for λc=9.2 μm at 77K). Finally, first results on p-on-n focal plane
arrays realized at CEA-LETI will be presented.
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