Implementation of a computer-controlled MOVPE system to grow epitaxial CMT

Abstract

A fully computer-controlled system has been constructed to high vacuum standards to grow cadmium mercury telluride (CMT) by metalorganic vapour phase epitaxy (MOVPE). Computer control facilitates reproducibility of growth conditions from run to run, automates data logging, and allows for a high degree of versatility in device structures that may be grown. This paper outlines important features of the system's design. The interdiffused multilayer process (IMP), in which alternate submicron layers of CdTe and HgTe are grown and subsequently inter-diffused at the growth temperature, has been employed to grow epitaxial CMT. Dimethylcadmium (DMCd), diethyltelluride (DETe) and mercury vapour have been used as sources of the constituent elements. Smooth layer surfaces have been achieved with {111} A and 2° off {100} oriented CdTe substrates. A compositional variation along the layer in the flow direction within the reactor was observed. This has been significantly improved by optimising the reactor design to reduce entrance effects. The implementation of IMP with the present system has established that the compositional uniformity requirement (±0.5% over 1 cm 2) for device quality CMT can now be achieved with MOVPE. Preliminary Hall effect measurements of CMT epitaxial layers have indicated p-type conductivity compatible with mercury vacancies. The good quality of material attainable with the system was further demonstrated by the high electron mobility of a HgTe epitaxial layer.