Determination of AlAs optical constants by variable angle spectroscopic ellipsometry and a multisample analysis

Authors

• C. M. Herzinger, University of Nebraska-Lincoln
• H. Yao, University of Nebraska-Lincoln
• Paul G. Snyder, University of Nebraska-LincolnFollow
• F. G. Celii, Texas Instruments, Central Research Lab., Dallas, Texas
• Y. C. Kao, Texas Instruments, Central Research Lab., Dallas, Texas
• B. Johs, J. A. Woollam Co., Lincoln, Nebraska
• John A. Woollam, J. A. Woollam Co., Lincoln, NebraskaFollow

Document Type

Article

Date of this Version

5-1-1995

Comments

Published in J. Appl. Phys. 77 (9), 1 May 1995. Copyright 1995 American Institute of Physics. Used by permission.

Abstract

Using variable angle spectroscopic ellipsometry, optical constants for AlAs (1.4-5.0 eV) are presented which are simultaneously compatible with measured data from four different samples. The below-gap index values are compatible with published prism measured values. The second derivative spectrum are compatible with published values above the direct band gap. The AlAs spectra is Kramers-Kronig self-consistent over the measured range and is compatible with published values from 0.6 to 1.4 eV. The optical constants for thin (<50 >Å) GaAs caps on AlAs are shown to be different from bulk GaAs values and require special consideration when fitting ellipsometric data. For the thin GaAs caps, the E₁ and E₁+ Δ₁ critical-point structure is shifted to higher energies as previously observed for GaAs quantum wells. Bulk AlAs optical constants are shown to be different from those of a thin (~20 Å) AlAs barrier layer embedded in GaAs. The thin barrier layer exhibits a highly broadened critical-point structure. This barrier broadening effect (AlAs) and the thin cap shifting effects (GaAs) have implications for in situ growth control schemes which make use of the E₁ and E₁+ Δ₁, critical-point region.