Improved arsenic doping in metalorganic chemical vapor deposition of HgCdTe and in situ growth of high performance long wavelength infrared photodiodes

Controlled and effective p-type doping is a key ingredient for in, situ growth of high performance HgCdTe photodiode detectors. In this paper, we present a detailed study of p-type doping with two arsenic precursors in metalorganic chemical vapor deposition (MOCVD) of HgCdTe. Doping results from a new precursor tris-dimethylaminoarsenic (DMAAs), are reported and compared to those obtained from tertiarybutylarsine (TBAs). Excellent doping control has been achieved using both precursors in the concentration range of 3 x 10(15)-5x10(17) cm(-3) which is sufficient for a wide variety of devices. Arsenic incorporation efficiency for the same growth temperature and partial pressure is found to be higher with DMAAs than with TBAs. For doping levels up to 1 x 10(17) cm(-3), the alloy composition is not significantly affected by DMAAs. However, at higher doping levels, an increase in the x-value is observed, possibly as a result of surface adduct formation of DMAAs dissociative products with dimethylcadmium. The activation of the arsenic as accepters is found to be in the 15-50% range for films grown with DMAAs following a stoichiometric anneal. However, a site transfer anneal increases the acceptor activation to near 100%. Detailed temperature dependent Hall measurements and modeling calculations show that two shallow acceptor levels are involved with ionization energies of 11.9 and 3.2 meV. Overall, the data indicate that DMAAs results in more classically behaved acceptor doping. This is most likely because DMAAs has a more favorable surface dissociation chemistry than TBAs. Long wavelength infrared photodiode arrays were fabricated on P-on-n heterojunctions, grown in situ with iodine doping from ethyl iodide and arsenic from DMAAs on near lattice matched CdZnTe (100) substrates. At 77K, for photodiodes with 10.1 and 11.1 mu m cutoff wavelengths, the average (for 100 elements 60 x 60 mu m(2) in size) zero-bias resistance-area product, R(0)A are 434 and 130 ohm-cm(2), respectively. Quantum efficiencies are greater than or equal to 50% at 77K. These are the highest R(0)A data reported for MOCVD in situ grown photodiodes and are comparable to state-of-the-art LPE grown photodiodes processed and tested under identical conditions.