STUDIES OF THIN STRAINED INAS, ALAS, AND ALSB LAYERS BY SPECTROSCOPICELLIPSOMETRY

The optical constants for thin layers of strained InAs, AlAs, and AlSb have been investigated by spectroscopic ellipsometry and multi-sample analyses. These materials are important for high-speed resonant tunne ling diodes in the AlAs/InAs/In0.53Ga0.47As and AlSb/InAs material sys tems. Understanding the optical properties for these thin layers is im portant for developing in situ growth control using spectroscopic elli psometry. Ex situ room-temperature measurements were made on multiple samples. The resulting fitted optical constants are interpreted as app arent values because they are dependent on the fit model and sample st ructure. These apparent optical constants for very thin layers can be dependent on thickness and surrounding material, and are generally app licable only for layers found in a similar structural context. The cri tical point features of optical constants for the strained layers and for the thin unstrained cap layers were found to differ from bulk valu es, and three principle effects (strain, quantum confinement, and thin -barrier critical-point broadening) have been identified as responsibl e. Of these three, the broadening of the E(1) and E(1)+Delta(1) critic al points for thin barrier material is the newest and most pronounced. This thin barrier effect is shown to be a separate effect from strain , and is also observable for the AlAs/GaAs system. (C) 1996 American I nstitute of Physics.