Metalorganic chemical vapor deposition of HgCdTe p/n junctions using arsenic and iodine doping

We report new results on metalorganic chemical vapor deposition (MOCVD)in situ growth of long wavelength infrared (LWIR) P-on-n and medium wavelength infrared (MWIR) n-on-P HgCdTe heterojunction photodiodes using the interdiffused multilayer process (IMP). The n-type regions are doped with iodine using the precursor ethyl iodide (El). I-doped HgCdTe using El has mobilities higher than that obtained on undoped background annealed films and are comparable to LPE grown In-doped HgCdTe. The p-type layers are doped with arsenic from either tertiarybutylarsine (TBAs) or a new precursor,tris-dimethylaminoarsenic (DMAAs). The substrates used in this work are lattice matched CdZnTe oriented (211)B or (100)4°→«110». Junction quality was assessed by fabricating and characterizing backside-illuminated arrays of variable-area circular mesa photodiodes. This paper presents four new results. First, carrier lifetimes measured at 80K on arsenic doped single HgCdTe layers are generally longer for films doped from the new precursor DMAAs than from TBAs. Second, we present data on the first P-on-n HgCdTe photodiodes grownin situ with DMAAs which have R0A products limited by g-r current at 80K for λco = 7–12 μm, comparable to the best R0A products we have achieved with TBAs. Third, we report the first experimental data on a new HgCdTe device architecture, the n-on-P heterojunction, with a wide gap p-type layer which allows radiation incident through the substrate to be absorbed in a narrower gap n-type layer, thereby eliminating interface recombination effects. With the n-on-P architecture, MWIR photodiodes were obtained reproducibly with classical spectral response shapes, high quantum efficiencies (70-75%) and R0A products above 2 x 105 ohm-cm2 for λco = 5.0 μm at 80K. Fourth, we report 40K data for LWIR P-on-n HgCdTe heterojunction photodiodes (using TBAs), with R0A values of 2 x 104 ohm-cm2 for λco = 11.7 μm and 5 x 105 ohm-cm2 for λco - 9.4 μm. These are the highest R0A values reported to date for LWIR P-on-n heterojunctions grownin situ by MOCVD.