The hydrogen transport vapour-phase epitaxy growth of CdTe on ZnTe/GaAs hyb
rid substrates for the realisation of detector-grade epilayers is reported.
Growth rates close to 10 mum/h were achieved by growing CdTe at around 770
degreesC and with the source temperature at 827 degreesC. The crystalline
structure of the as-grown epilayers was investigated by double crystal X-ra
y diffraction measurements. Despite the large epilayer/substrate lattice mi
sfit, the crystalline perfection of CdTe layers rapidly improves with the t
hickness; indeed, FWHM values of the (40 0)CdTe peak down to 59 arcsec are
obtained for similar to 30 mum thick samples; this value compares well with
results published in the literature for best epitaxial CdTe. Corresponding
ly, mirror-like and nearly featureless surfaces were observed. CdTe samples
grown below 650 degreesC are p-type and low resistive [rho less than or eq
ual to 20 Omega cm at room temperature (RT)], whilst at temperatures > 650
degreesC the layers are n-type. In this case, resistivity similar to 10(6)
Omega cm are obtained for growth between 675 degreesC and 700 degreesC, but
lower values result above 700 degreesC, However, resistivity in the 10(4)-
10(5) Omega cm range are achieved in the latter case by increasing the epil
ayer thickness up to 30 mum. This behaviour is ascribed to the occurrence o
f Ga-related donors in CdTe, the latter originating by the diffusion of Ga
atoms from the GaAs substrate. These donors are almost compensated by resid
ual accepters in CdTe, giving rise to the medium/high resistivity values ob
served for some of the samples. The detection capability of the material ha
s been demonstrated by time-of-flight (TOF) measurements performed on a dev
ice made by an n-CdTe epilayer. The analysis of the TOF collected charge as
a function of the applied reverse voltage gives mu tau approximate to 4.9
x 10(-6)cm(2)/V for this material. Such low value arises from a large elect
ron trapping in CdTe epilayers, consistently with the similar to 10(18)cm-(
3) density of compensated (positively charged) donors. (C) 2001 Elsevier Sc
ience B.V. All rights reserved.