No abstract

Epitaxial PbSe layers on Si(111) relax nearly completely owing to the easy dislocation glide in the main ͕100͖ ͗110͘ glide system. Threading dislocations introduced by the thermal mismatch strains are able to move distances of several cm and to escape at the edges of the samples. Etch-pit densities as low as 10 6 cm 22 were obtained in layers with a thickness of d 4 mm. The etch-pit density scales with 1͞d 2 , which may be understood as a consequence of the annealing step and of the high mobility of dislocations. By applying several anneal cycles, threading dislocation densities of essentially zero should result. [S0031-9007(97)

Epitaxial growth of PbSe on (111)- and (100)-oriented Si substrates without an intermediate buffer layer is studied. It is found that on Si(111) the orientation of the IV-VI layer can by varied from (100) at 200 °C to (111) at 400 °C substrate temperature. On Si(100), only (100)-oriented layers were obtained for the whole temperature range. (100)-oriented layers with thicknesses above 0.5 μm were cracked due to thermally induced mechanical strain on cooldown to room temperature. This strain cannot be relaxed by dislocation glide in the first glide systems as it is the case for (111)-oriented layers. The structural quality of (100)-oriented PbSe layers on Si(100) and Si(111) is inferior compared to layers grown with an intermediate BaF2/CaF2 or CaF2 buffer layer. This implies that the covalent/ionic PbSe/Si interface seems to impede high-quality epitaxy, contrary to the well known ionic/ionic IV-VI/IIa-fluoride interface.

MBE growth and infrared device fabrication with epitaxial lV-VI layers on Si-substrates is reviewed and some new results are included. Epitaxy is achieved using a stacked BaF2/CaF2 or CaF2 buffer layer. While photolithographic delineation techniques are somewhat difficult with BaF2 (whiôh is soluble in water), reliable wet-etching techniques are easy with the CaF2 buffer. Photovoltaic IV-VI sensors on Si(1 1 1 ) substrates are fabricated with cut-off wavelengths covering the whole atmospheric 3-5 and 8-1 4 im window. They offer the possibility for low cost infrared focal plane arrays with sensitivities similar to MCT, but with much less demanding material processing steps. This is because the structural quality of even heavily lattice mismatched lV-Vl layers suffices to fabricate devices with good sensitivities, and because the bandgap in Pb1SnSe for the 8-12 jim range depends much less on composition x than for the corresponding Hg1CdTe. A 13 mm long linear array with 10.5 jim cutoff wavelength has inhomogeneities in cut-off below 0.1 .tm. Some arrays were grown on prefabricated active Sisubstrates containing the whole read-out circuits. Process temperatures were below 450°C because of the Almetallization. First thermal images using these chips are demonstrated.The induced mechanical strain due to the different thermal expansions relaxes down to cryogenic temperatures even after many temperature cycles. This is due to dislocation glide in the main {100}-glide planes even at low temperatures.

No abstract