Transparent Gallium-Based Oxide Ceramics
Date
2022-05
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Publisher
New York State College of Ceramics at Alfred University. Inamori School of Engineering.
Abstract
Transparent ceramics have been developed and studied for more than 50 years; however, very few efforts have been made in making transparent ceramics semiconducting. Gallium-based oxide materials including, β-Ga2O3 and MgGa2O4 are one of the few materials being considered for semiconducting transparent oxide applications, and which attract significant attention due to their potential as electronic materials with unprecedented performance. This study provides preliminary experimental results on the fully densified (transparent) β-Ga2O3, β-(AlxGa1-x)2O3 and MgGa2O4 ceramics successfully fabricated via the Spark Plasma Sintering (SPS or Pulsed Electric Current Sintering) approach.
Both β-Ga2O3 and β-(AlxGa1-x)2O3 have a monoclinic crystalline structure which leads to non-isotropic refractive index. Dense grain structure and small grain size are the two key requirement for obtaining optical transparency in these two material systems. MgGa2O4 belongs to the spinel family with a cubic crystalline structure that do not suffer from birefringence and small grain size is no longer needed as a solution to this problem. Gallium oxide compound (β-Ga2O3 and MgGa2O4) are very reactive at high sintering temperature, which may lead to the reduction reaction when in contact with graphite or exposed to the vacuum environment. To avoid this problem, Mo foil and BN powder have been applied to reduce such reaction. In addition, BN has also served as a buffer layer, which absorbed the thermal and mechanical shock during SPS processing, which have been thought to be the cause of cracking in many sintered ceramic samples at the very end of the sintering process upon cutting off the electrical power supply.
High total transmittance of 84% has been achieved in the non-cubic β-Ga2O3 transparent ceramics at 1000nm, whereas high in-line transmittance of 73.3% at ~1.2 µm has been demonstrated in cubic MgGa2O4 transparent ceramics. Detailed procedures on how to fabricate these transparent ceramics are presented in this work. Characterizations results related to to optical properties of fabricated transparent ceramics (photoluminescence, thermoluminescence) are presented to demonstrate potential applications. Overall, it is believed that the transparent ceramics mentioned here will bring new opportunities to the transparent ceramics field, especially for electro-optic applications.
Description
Thesis completed in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Ceramic Engineering at the Inamori School of Engineering, New York State College of Ceramics at Alfred University
Type
Thesis
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Keywords
Transparent ceramics, Ceramic engineering