METALORGANIC CHEMICAL-VAPOR-DEPOSITION OF HGCDTE FOR PHOTODIODE APPLICATIONS

Metalorganic chemical vapor depositon (MOCVD) in situ growth of p-on-n junctions for long wavelength infrared (LWIR) and medium wavelength i nfrared (MWIR) photodiodes is reported. The interdiffused multilayer p rocess was used for the growth of the HgCdTe junctions on CdTe and CdZ nTe substrates. The n-type region was grown undoped while the p-type l ayer was arsenic doped using tertiarybutylarsine. Following a low temp erature anneal in Hg vapor, carrier densities of (0.2-2) x 10(15) cm(3 ) and mobilities of (0.7-1.2) x 10(5) cm(2)/V-s were obtained for n-ty pe LWIR (x similar to 0.22) layers at 80K. Carrier lifetimes of these layers at 80 K are similar to 1-2 mu s. For the p-type region arsenic doping was controlled in the range of (1-20) x 10(16) cm(-3). Arsenic doping levels in the junctions were determined by calibrated secondary ion mass spectroscopy depth profile measurements. Composition and dop ing of the p-on-n heterojunctions could be independently controlled so that the electrical junction could be located deeper than the change in the composition. The graded composition region between the narrow a nd wide (x = 0.28-0.30) bandgap regions are 1-2 mu m depending on the growth temperature. Backside-illuminated variable-area circular mesa p hotodiode arrays were fabricated on the grown junctions as well as on ion implanted n-on-p MWIR junctions. The spectral responses are classi cal in shape. Quantum efficiencies at 80K are 42-77% for devices witho ut anti-reflection coating and with cutoff wavelengths of 4.8-11.0 mu m. Quantum efficiencies are independent of reverse bias voltage and do not decrease strongly at lower temperatures indicating that valence b and barrier effects are not present. 80K R(0)A of 15.9 Omega-cm(2) was obtained for an array with 11.0 mu m cutoff. Detailed measurements of the characteristics of the MOCVD in situ grown and implanted photodio des are reported.