|About this Abstract
||2010 Electronic Materials Conference
||TMS 2010 Electronic Materials Conference
||II7, High-Quality (211)B CdTe on (211) Si Substrates Using Metal-Organic Vapor-Phase Epitaxy
||Sunil Rao, Shashidhar Shintri, Justin Markunas, Randolph Jacobs, Ishwara Bhat
|On-Site Speaker (Planned)
(211)B CdTe is the preferred buffer layer for epitaxial growth of device quality (211)B Hg<sub>1-x</sub>Cd<sub>x</sub>Te films on (211) Si substrates. Molecular beam epitaxy (MBE) has been used to obtain high quality (211)B CdTe films on (211)Si substrates. The 19% lattice-mismatch between CdTe and Si has limited the threading dislocation (TD) density in state-of-the-art MBE-grown material in the mid-10<sup>5</sup>cm<sup>-2</sup> to low-10<sup>6</sup>cm<sup>-2</sup> range. Higher growth temperatures (>400<sup>o</sup>C) and techniques like epitaxial lateral overgrowth (ELO) used during metal-organic vapor-phase epitaxy (MOVPE) could help in further reducing the TD density. We have previously reported on the successful MOVPE growth of (211)B CdTe on Si substrates using Ge and ZnTe interfacial layers. A cyclic annealing procedure has been used to improve crystal quality during growth of 8Ám – 10Ám thick CdTe films. The cyclic annealing enhances threading dislocation motion and increases the probability of dislocation interaction and annihilation reactions. Everson etch pit density (EPD) is used to characterize the TD density in (211)B CdTe films. A reduction in Everson EPD was observed for CdTe films grown using the cyclic annealing procedure, EPD was 1x10<sup>7</sup>cm<sup>-2</sup> for a 5Ám thick un-annealed film compared with 4x10<sup>6</sup>cm<sup>-2</sup> for a 5Ám thick film grown using a cyclic annealing procedure. The lowest EPD observed in this study was 2x10<sup>6</sup>cm<sup>-2</sup> for an 8Ám thick film. The good crystal quality of the grown films was also characterized by a low x-ray diffraction (XRD) (422) rocking-curve full-width–at-half-maximum (FWHM) of 85 arc-s. This FWHM value is superior to the previous best FWHM value of 140 arc-s reported for MOVPE grown (211)B CdTe/Si. One of the current challenges in our MOVPE process is the rough surface morphology of the grown CdTe films. The films display an orange-peel-like surface texture when observed using a Nomarski contrast optical microscope. In addition, polycrystalline lumps (density varying from 1x10<sup>3</sup>cm<sup>-2</sup> to 1x10<sup>5</sup>cm<sup>-2</sup>) are also observed on the surface. A modification in the growth temperature from 325<sup>o</sup>C to 350<sup>o</sup>C has enabled us to eliminate these polycrystalline lumps. Efforts are currently underway to optimize the other growth process parameters in order to improve the over-all surface morphology. This work was partially supported by US Army STTR contract W911NF-07-C-0105 through Agiltron Inc. (Dr. Matthew Erdtmann) and US ARMY STTR contract W911NF-08-C-0071 through Brimrose Corporation. Many discussions with Dr. P. Wijewarnasuriya of ARL are also appreciated. We thank Dr. William Clark of ARO for all his encouragement.