P-on-n arsenic-activated junctions in MOCVD LWIR HgCdTe/GaAs

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Abstract
Low-leakage high-performance photovoltaic detectors were fabricated from long-wavelength infrared (LWIR) HgCdTe epitaxial material grown by metal-organic chemical vapour deposition (MOCVD) on GaAs substrates. Layers were grown by two different MOCVD techniques, a conventional alloy growth and an interdiffused multiple-layer growth. MOCVD HgCdTe layers were characterised by background electron concentrations of (1-3)*1015 cm-3 with electron mobilities up to 200000 cm2 V-1 s-1 at 77 K. Surface and cross-section dislocation densities were 106-107 cm-2 and occasionally (4-5)*105 cm-2. GaAs substrates were (100) and (111B) misoriented towards 110. The layer structure in which the devices were fabricated consisted of an absorbing LWIR HgCdTe layer grown on a buffer of CdTe. A thin layer (1-2 mu m) of wide-band-gap HgCdTe was grown last. Devices were fabricated in a single as well as double layers using a mesa geometry with a native oxide passivation. Junctions were formed at 2-3 mu m depth by a low-energy arsenic implant ( approximately 100 keV) which behaved as a finite diffusion source during the post-implant anneal. The best measured zero-bias resistance-area products (R0A) at 77 K were 1.67 Omega cm2 for the alloy layers for a cut-off wavelength of lambda c=14.94 mu m and 7.22 Omega cm2 for the interdiffused multiple layers for lambda c=15.92 mu m at 77 K. The results indicated a definite device performance improvement in double-layer compared to single-layer structures. Analysis of the transport properties for a device fabricated in a single layer with a cut-off wavelength of lambda c=8.35 mu m at 77 K and 9.1 mu m at 40 K suggested that the deviation from thermal processes occurs at temperatures of approximately 40 K.