Orientation Dependence of CdTe/Si Grown by MBE
- PDF / 2,514,348 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 37 Downloads / 235 Views
ABSTRACT In this study CdTe (111)B was grown by molecular beam epitaxy on vicinal Si(001) substrates, with a variety of substrate tilt angles (6), and tilt directions (0) relative to [110]. Layer quality, and content of double-domain and microtwin defects were evaluated by double crystal rocking curve (DCRC) full width at half maximum (FWHM) and x-ray diffraction, respectively. Transmission electron microscopy (TEM) was used to study interface quality and the nature of structural defects as a function of epilayer thickness. In the present investigation, substrate preparation and growth conditions, particularly initiation conditions, are correlated with Si (001) tilt. It has been found that oxide desorption processes can depend strongly on 0, especially for larger values of 0 (> 40 ). Currently, we routinely produce single domain, twinfree CdTe(l 1I )B epilayers on vicinal Si (001) substrates. INTRODUCTION Investigation of heteroepitaxial growth of CdTe on Si is motivated by the need for alternative substrates of sufficient crystalline quality for subsequent growth and processing of Hg,-0 CdxTe-based infrared detecting devices.
CdTe/Si substrates offer substantial advantages
over conventional, bulk CdZnTe substrates. These include: lower cost; improved mechanical strength; availability of large area wafers; thermal expansion matching to Si readout devices; integration of Hg,-.CdxTe detectors and Si signal processors onto a single chip for an extremely compact focal plane array. Additional applications of CdTe/Si material are soft x-ray detecting devices and advanced solar cells. Previous studies have shown that CdTe grown directly on nominal Si (001) grows preferentially in the (111) orientation.' However, because of the change in surface symmetry from the Si (001) substrate to the CdTe (111) growth plane, the CdTe epilayer is prone to formation of double domain defects in addition to high densities of lamellar twins. The double domain regions are related by a 900 rotation about [111] i.e. CdTe [11T] 1I Si [TI0] and CdTe [11T] II Si [110]. Lamellar twins are related by a 1800 rotation about [111] and form planar regions parallel to the growth plane i.e. CdTe [1 IT] I Si [1TO] or Si [T10]. It has been found2 that employing Si substrates with surfaces tilted away from (001) can significantly affect the formation of both double domain and twinning defects. Two tilt parameters, 0 and 4), are used to uniquely specify tilt magnitude and direction, where 0 is defined as the angle between the surface normal and the [001] direction, and 4) is defined as the azimuthal angle with respect to [110]. The use of tilted Si substrates (0 _>0.50) results in CdTe epilayers with double domain regions only very near (- 30-50nm) the interface. As the deposition continues, one alignment tends to dominate, specifically CdTe [112 I Si [T10]. 343 Mat. Res. Soc. Symp. Proc. Vol. 399 ©1996 Materials Research Society
Along this orientation the lattice mismatch is 3.4% compared with - 19% in the orthogonal direction. Electron micrographs cle
Data Loading...
