Heteroepitaxiai Growth Of CdTe And CdHgTe By Close-Spaced Vapor Transport

Reactive close spaced vapor transport in hydrogen has been used to deposit II-VI compound semiconductors on (0001) sapphire substrates. The CdTe grown layer are (111) oriented with some twinning as clearly shown by Laue diffraction patterns. For a substrate at 500°C the growth process is three dimensional and in a coalescence regime leading to highly facetted and oriented pyramidal surfaces with a (111) growth axis. From the DDX measured value, 2000 arc-sec, one mights infer that the crystallinity is relatively poor. However FL spectra show near-band-edge and exciton emission lines with a linewidth of less 0.6 meV at 2K. Also n-type In-doped films have typically electron concentration of 10 15 -10 16 cm -3 with mobilities of few hundreds cm2 V-1 5-1 at room temperature. The CdTe epilayers on GaAs (100) are either (111) or (100), or a (111) + (100) mixture.The layers have textured surfaces with pyramids. In the (111) oriented growth the basis of the pyramid is triangular with epitaxial relation CdTe (211)//GaAs (011). High resolution TEM studies reveal sharp interface. The as-grown layers are n type (1015 - 1017 cm -3 ) with mobility at 300 K of 390 cm 2 V -1 s -1 , and the P. spectra shows near-band-edge recombination with line-width of 1.5 meV at 2K. In relevance to I.R. focal plane array technology, heteroepitaxy of CdHgTe on GaAs is obtained by growing HgTe upon one layer of CdTe with a subsequent interdiffusion heat-treatment process. Hall mobilities of 5000 (room temperature) and 8000 (20K) cm2 V -1 .5 -1 for (100) layers are measured.