CdTe doped with Zn grown on Si(111) and Si(211) using the closed space sublimation method
Cadmium telluride (CdTe) doped with zinc (Zn) has been used for the fabrication of X-ray imaging devices. CdTe allows the device to have the same image quality at a lower X-ray dose. When silicon is used as a substrate for CdTe growth, this reduces the cost and allows the readout circuitry to be fabricated on the same substrate. However, material quality and device performance needs to be addressed since the lattice parameters of CdTe (6.482 Å) and Si (5.431 Å) result in a 19% lattice mismatch. In this work, CdTe doped with Zn is deposited on Si (211) and Si (111) substrates by the closed-space sublimation (CSS) technique. The CSS method has an advantage over other techniques in terms of cost and growth rate, but represents a challenge when growing high quality films. The nanoheteroepitaxy (NHE) technique makes it possible to grow CdTe on Si substrates with fewer defects at the CdTe/Si interface and in the resulting epilayer. Electron beam lithography is used to pattern three different pillar diameters (200 nm, 100 nm, and 50 nm) on Si substrates (Si(211) and Si(111)), and two different pitch to diameter ratios (p/d=3 and p/d=2) to examine the growth of CdTe doped with 5 and 10 percent Zn. Scanning electron microscopy (SEM) is used to examine the morphology of the CdTe growth and X-ray diffraction (XRD) is used to identify the orientation of the film and the quality of the structure of the CdTe film doped with 5% Zn. TEM characterization is used to examine the planar structure at the interface, the misorientation at interface and the type of defects in the CdTe film growth. SEM results indicate when the pitch/diameter pattern ratio is decreased from 3 to 2, the morphology of the CdTe growth is improved. As expected and confirmed with XRD data, the quality improves as the pattern diameter is reduced, especially when Zn doping is increased from 5% to 10%. Transmission electron microscopy (TEM) is used to study the CdTe/Si interface and the resulting misorientation of the CdTe/Si interface, ranges from 0.2° to 1.2°.
Valdez, Jose A., "CdTe doped with Zn grown on Si(111) and Si(211) using the closed space sublimation method" (2016). ETD Collection for University of Texas, El Paso. AAI10151396.