Long Wavelength Infrared, Molecular Beam Epitaxy, HgCdTe-on-Si Diode Performance M. CARMODY, 1,4 J.G. PASKO, 1 D. EDWALL, 1 M. DARASELIA, 1 L.A. ALMEIDA, 2 J. MOLSTAD, 2 J.H. DINAN, 2 J.K. MARKUNAS, 2 Y. CHEN, 3 G. BRILL, 3 and N.K. DHAR 3 1.—Rockwell Scientific Company, Camarillo, CA 93012. 2.—United States Army CECOM RDEC NVESD, Fort Belvoir, VA 22060. 3.—Army Research Laboratory, Adelphi, MD 20783. 4.—E-mail: mcarmody@rwsc.com In the past several years, we have made significant progress in the growth of CdTe buffer layers on Si wafers using molecular beam epitaxy (MBE) as well as the growth of HgCdTe onto this substrate as an alternative to the growth of HgCdTe on bulk CdZnTe wafers. These developments have focused primarily on mid-wavelength infrared (MWIR) HgCdTe and have led to successful demonstrations of high-performance 1024  1024 focal plane arrays (FPAs) using Rockwell Scientific’s double-layer planar heterostructure (DLPH) archi- tecture. We are currently attempting to extend the HgCdTe-on-Si technology to the long wavelength infrared (LWIR) and very long wavelength infrared (VLWIR) regimes. This is made difficult because the large lattice-parameter mismatch between Si and CdTe/HgCdTe results in a high density of threading dislocations (typically, 5E6 cm -2 ), and these dislocations act as conductive pathways for tunneling currents that reduce the R o A and increase the dark current of the diodes.To assess the current state of the LWIR art, we fabricated a set of test diodes from LWIR HgCdTe grown on Si. Silicon wafers with either CdTe or CdSeTe buffer layers were used.Test results at both 78 K and 40 K are presented and discussed in terms of threading dislocation density. Diode characteristics are compared with LWIR HgCdTe grown on bulk CdZnTe. Key words: HgCdTe-on-Si, long wavelength infrared (LWIR), molecular beam epitaxy (MBE), diode performance Journal of ELECTRONIC MATERIALS, Vol. 33, No. 6, 2004 Special Issue Paper 531 (Received October 7, 2003; accepted December 15, 2003) INTRODUCTION The highest quality, long wavelength infrared (LWIR) HgCdTe is grown by molecular beam epitaxy (MBE) on near-lattice-matched CdZnTe substrates, and Rockwell Scientific (Camarillo, CA) has helped pioneer this technology. However, the relatively high cost and size limitation of CdZnTe substrate wafers have prompted a search for a low-cost alternative substrate that is suitable for high volume produc- tion. 1,2 Silicon wafers offer many advantages be- cause of their low cost, large available sizes, high mechanical strength, industrial maturity, and the ability to thermally match to the readout integration chip. 1–5 Several material-related challenges have, thus far, prevented the realization of this potential. First, the lattice-parameter mismatch between Si and HgCdTe is 19% (a Si = 5.43 Å, a CdTe = 6.48 Å, and a HgTe = 6.453 Å). Second, the thermal-expansion co- efficient mismatch between Si and HgCdTe is signif- icant. These differences result in a high density of threading dislocations. Epitaxial layers of ZnTe and CdTe have been grown on Si wafers prior to growth of HgCdTe to buffer this lattice-parameter misfit. Nevertheless, typical HgCdTe epitaxial layers grown by MBE at Rockwell Scientific on CdTe/Si have threading dislocation densities of 10 6 -10 7 cm -2 . It has been found that R o A values for photodiodes de- crease when dislocation densities are above mid-10 5 cm -2 . 16–18 Mid-wavelength infrared (MWIR) layers with these high dislocation densities can be used for