Optical constants of polycrystalline Al0.25Ga0.75P and Al0.9Ga0.1As determined by variable-angle spectroscopic ellipsometry

Author:

Quispe D.1ORCID,Eng B.2,Kim M.2ORCID,Onno A. L.3ORCID,Coppa B. J.3,Yu Z. J.3ORCID,Lee M. L.2ORCID,Holman Z. C.3ORCID

Affiliation:

1. School for Engineering of Matter, Transport and Energy, Arizona State University 1 , Tempe, Arizona 85287, USA

2. Department of Electrical and Computer Engineering and Holonyak Micro & Nanotechnology Laboratory, University of Illinois Urbana-Champaign 2 , Urbana, Illinois 61801, USA

3. School of Electrical, Computer and Energy Engineering, Arizona State University 3 , Tempe, Arizona 85287, USA

Abstract

The optical constants of single-crystal AlxGa1−xP and AlxGa1−xAs have been widely studied at various Al compositions but have not yet been thoroughly investigated as polycrystalline materials. Using variable-angle spectroscopic ellipsometry, we estimate and analyze the optical constants of polycrystalline Al0.25Ga0.75P and Al0.9Ga0.1As that were non-epitaxially deposited at deposition temperatures of either 250 or 420 °C, and with various dopant species, dopant concentrations, and V/III flux ratios. For wavelengths of 350–400 nm, decreasing the V/III ratio increases the refractive index of Be-doped polycrystalline Al0.25Ga0.75P. For wavelengths >500 nm, as the targeted Be dopant concentration increases for polycrystalline Al0.25Ga0.75P, the amount the extinction coefficient increases and the indirect bandgap decreases depends on the V/III ratio. Furthermore, Si-doped polycrystalline Al0.25Ga0.75P has significantly smaller extinction coefficient values than when it is Be-doped, for the same V/III ratio and targeted doping concentration, at wavelengths >500 nm. Based on our findings, we hypothesize that the dopant species, dopant concentration, and the V/III ratio dictate various types of defect concentrations, which then affect the optical constants and indirect bandgap of polycrystalline Al0.25Ga0.75P. Additionally, for wavelengths >500 nm, we find that polycrystalline Al0.25Ga0.75P and Al0.9Ga0.1As have the lowest extinction coefficient values when deposited at 420 °C, as opposed to 250 °C. Thus, we hypothesize that the deposition temperature is the most significant factor in dictating the optical constants of these polycrystalline III-Vs. Ultimately, this work demonstrates alternative methods to tune the optical constants of polycrystalline Al0.25Ga0.75P and Al0.9Ga0.1As, as opposed to tuning the Al composition.

Funder

National Science Foundation

U.S. Department of Energy

Publisher

AIP Publishing

Subject

General Physics and Astronomy

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