MODELING OF IN-SITU MONITORED LASER REFLECTANCE DURING MOCVD GROWTH OF HGCDTE

An effective way to in situ monitor the metalorganic chemical vapor de position (MOCVD) of HgCdTe/CdTe/ZnTe on GaAs or GaAs/Si substrates is presented. Specular He-Ne laser reflectance was used to in situ monito r the growth rates, layer thickness, and morphology for each layer in the grown multilayer structure. In situ monitoring has enabled precise measurements of ZnTe nucleation and CdTe buffer layer thicknesses. Mo nitoring the constancy of reflectance during the thicker CdTe buffer g rowth where absorption in the CdTe reduces reflectance to just the sur face component has led to optimum buffer growth ensuring good quality of subsequently grown HgCdTe. During the interdiffused multilayer proc ess (IMP) HgCdTe growth, because multiple interfaces are present withi n the absorption length, a periodic reflectance signal is maintained t hroughout this growth cycle. A theoretical model was developed to extr act IMP layer thicknesses from in situ recorded experimental data. For structures that required the growth of a larger band gap HgCdTe cap l ayer on top of a smaller band gap active layer, in situ monitored refl ectance data allowed determination of alloy composition in the cap lay er as well. Continuous monitoring of IMP parameters established the st ability of growth conditions, translating into depth uniformity ofthe grown material, and allowed diagnosis of growth rate instabilities in terms of changes in the HgTe and CdTe parts of the IMP cycle. A unique advantage of in situ laser monitoring is the opportunity to perform ' interactive'' crystal growth, a development that is a key to real time MOCVD HgCdTe feedback growth control.