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Narrow-gap IV-VI lead chalcogenide layers grown on Si substrates with the aid of an intermediate CaF,/BaF, buffer relax the thermal-mismatch-induced strain by misfit dislocations which glide on the primary (100) glide planes inclined 54.7' with respect to the (111) surface. Macroscopic strain measurements show near complete mismatch strain relaxation down to cryogenic temperatures even after multiple cycling for binary PbSe, while ternary PbSe,-,Te, (x = 0.4) strains elastically below room temperature. The morphology of the resulting dislocation steps is revealed by scanning tunnelling microscopy for the IV-VIS and atomic force microscopy for the fluoride buffer, and the number of dislocation step lines agrees with the calculated thermal strain relaxation. FZ 1 pm h-l, and substrate temperatures are in the range 300 to 400°C. X-ray rocking curve linewidths are N 180 arcsec for the 2-3 pm thick layers used [2, 51.s337

Heteroepitaxial CuInSe2 (CIS) layers have been directly grown on Si substrates by molecular beam epitaxy. Epitaxial growth is achieved by using a proper thermal treatment of the substrate prior to the growth and also during the initial stage of CIS growth. (100)-oriented and (112)-oriented CIS layers with chalcopyrite crystal structure, and free from impurity phases have been obtained on Si(100) and Si(111), respectively. Different methods have been used to study the growth kinetics and structural quality of the epitaxial layers. Twinning in (112)-oriented CIS layers depends on the deposition recipe. A Rutherford backscattered ion channeling minimum yield of about 13%, and an x-ray rocking-curve width of about 900 arcsec have been measured for a 0.4 μm thick heteroepitaxial CIS(112) layer on Si(111) substrate.

Epitaxial CuIn3Se5 layers were grown on CuInSe2/Si(111) substrates by molecular beam epitaxy. Photoemission spectra of (112)-oriented CuIn3Se5 and CuInSe2 epitaxial layers were studied and the structures in the upper valence band are correlated with the Cu 3d and Se 4p density of states. The main valence band of CuInSe2 exhibits the three peak structure (consistent with theory) while a broadband with a shoulder is observed for the CuIn3Se5 phase. Electron channeling and x-ray diffraction confirmed the epitaxial growth of (112)-oriented layer. Surface and bulk composition analyses, position of valence band maxima, and a Se related vibrational mode at 153 cm−1 in Raman scattering measurements established the growth of the CuIn3Se5 phase.

MBE growth of epitaxial IV-VI lead salt layers on Si (111) substrates and fabrication of photovoltaic infrared devices in the layers is reviewed. IV-Vi on Si IR sensors have potential as a low-cost technique of fabrication of large IR focal plane arrays for both t h e 3-5 pm and 8-12 pm ranges because of t h e easy fabrication procedure and because uniformity problems are much less severe in IV-VIS due to the weaker composition dependence of the bandgap compared with Cd, -,Hg,Te. Sensor arrays are fabricated in 2-4 pn thick PbTe. PbS, -,Se, and Pb, _.Eu,Se for 3 4 p m and in Pb,-,%,Se for 8-12 pm cut-off. An intermediate epitaxial stacked 0.2 pm thick CaF,BaF, bilayer serves for compatibility and helps to overcome the large lattice and thermal expansion mismatch between the Si substrate and the IV-VI layer. Perfectly smooth surfaces with surface defect concentrations down to 103cm-'. and x-ray rocking-curve linewidth of ~1 5 0 arcsec are obtained. Sensor arrays with 66 and 256 elements are described, the latter having been grown on standard Si chips with Ai metallization.