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.