Structural and electrical properties of CdTe layers grown on ZnTe/GaAs by hydrogen transport VPE

The structural and electrical characterisation of CdTe epilayers grown by H2 transport vapour phase epitaxy (H2T-VPE) on ZnTe/(100)GaAs is reported. Double-crystal X-ray diffraction measurements indicate the material high crystalline quality, leading to (400) peak FWHM of 59 arcsec for30 um thick epilayers. CdTe grown at temperatures T-D<650°C are p-type, but turn to n-type for T-D>650°C. For 650°C<T-D<700°C, room-temperature (RT) resistivity in the 10(5)-10(6) Ohm cm range is obtained. Hall measurements performed on n-type samples of different thicknesses grown at T-D=764°C show RT carrier concentrations in the 10^(14)-10^(11) cm^(-3) range. For a 22 um thick epilayer two donor states are found: the most abundant one almost compensates a 10^(18) cm^(-3) density of accepters; the second donor, having an ionisation energy E-D = 0.186 eV, determines the sample n-type properties, its concentration being similar to 10^(15) cm^(-3) A compensation ratio K greater than or equal to 0.9997 holds for this epilayer. It is suggested that Ga diffusing from GaAs into CdTe gives rise to the above donor states.