Hg1-xCdxTe (112) nucleation on silicon composite substrates

The epitaxial growth of Hg1-xCdxTe in the composition range 0.40<x<0.17 has been carried out on 3-inch CdTe/Si(112) substrates mounted on indium-free molybdenum substrate holders. Because this mounting configuration prevents the effective use of a direct thermocouple contact to control the sample temperature, and because a dramatic change in the surface emissivity of the sample occurs during the onset of HgCdTe nucleation, an alternative method for controlling the surface temperature is developed. We utilize reflection high-energy electron diffraction (RHEED) and a thermocouple ramping sequence to maintain a constant HgCdTe surface temperature. Due to the narrowness of the HgCdTe growth window, small variations in the surface temperature (similar to2degreesC) produce a slight but observable change in the RHEED pattern. Through careful observation of the RHEED images, an optimized thermocouple ramping process is obtained such that the RHEED pattern remained constant from the onset of HgCdTe nucleation. Structural and electrical characterization of these samples demonstrate the usefulness of the temperature ramping methodology. For middle wavelength infrared (MWIR) material, mobility measurements made on several n-type samples at 77 K range give values in the 2 x 10(4) - 4 x 10(4) cm(2)/Vsec range with doping levels in the low 10(14) cm(-3). Additionally, preliminary lifetime measurements made on one MWIR sample gives 2.8 musec. For long wavelenth infrared (LWIR) material, mobility measurements made on several n-type samples at 77 K give values in the 3 x 10(5) to 5 x 10(5) cm(2)/Vsec range with doping levels in the mid 10(15) cm(-3). Electrical, structural and defect characterization along with device results are presented with a focus on the optimization of the thermocouple ramping process. In addition, the efficacy of Si-based composite substrates for the technological advancement of large format infrared focal plane arrays will be discussed.