IntegratedIn Situ wafer and system monitoring for the growth of CdTe/ZnTe/GaAs/Si for mercury cadmium telluride epitaxy

Abstract

Reproducible improvements in the metalorganic vapor phase epitaxy (MOVPE) grown CdTe buffer quality have been demonstrated in a horizontal rectangular duct silica reactor by the use of integratedin situ monitoring that includes laser reflectometry, pyrometry, and Epison concentration monitoring. Specular He-Ne laser reflectance was used toin situ monitor the growth rates, layer thickness, and morphology for both ZnTe and CdTe. The substrate surface temperature was monitored using a pyrometer which was sensitive to the 2–2.6 μm waveband and accurate to ±1°C. The group II and group VI precursor concentrations entering the reactor cell were measured simultaneously using two Epison ultrasonic monitors and significant variations were observed with time, in particular for DIPTe. The surface morphology and growth rates were studied as a function of VI/II ratio for temperatures between 380 and 460°C. The background morphology was the smoothest for VI/IIratio in the vicinity of 1.5–1.75 and could be maintained using Epison monitors. Regularly shaped morphological defects were found to be associated with morphological defects in the GaAs/Si substrate. The x-ray rocking curve widths for CuK_α (531) reflections were in the range of 2.3–3.6 arc-min, with no clear trend with changing VI/II ratio. X-ray topography images of CdTe buffer layers on GaAs/Si showed a mosaic structure that is similar to CdTe/sapphire substrates. The etch pit density in Hg_1-xCd_xTe layers grown onto improved buffer layers was as low as 6 x 10⁶ cm^-2 for low temperature MOVPE growth using the interdiffused multilayer process.