학술논문
Cd1-x Cox Ga2 Se4 화합물 반도체의 결정구조 및 광학적 특성 연구 / Structural and Optical properties of Cd1-x Cox Ga2 Se4 compound semiconductors
Document Type
Dissertation/ Thesis
Author
Source
Subject
Language
Korean
Abstract
본 연구는 삼원 화합물 반도체인 CdGa2Se4와 묽은 자성반도체인 CoGa2Se4를 모체로 한 Cd1-xCoxGa2Se4 혼합 화합물 반도체의 기초 물성을 연구하기 위한 것으로서, 조성 0.0 ≤ ≤ 0.5 영역에서 의 변화에 따른 결정구조 변화 및 Co2+이온의 광학적 특성 변화를 조사하였다. Cd1-xCoxGa2Se4 결정 성장은 고순도(99.9999 %)의 구성 원소로부터 조성 0.0 ≤ ≤ 0.5 영역에서 용융법으로 이루어졌다. 결정구조는 조성 0.0 ≤ ≤ 0.5의 전 영역에서 정방정계 결정구조인 defect chalcopyrite구조였으며, 격자상수 와 의 조성의존성 특성은 Vegard법칙을 만족하는 선형적 관계식 = 5.7375 - 0.115, = 10.7775 + 0.125로 주어졌다. 또한 이들 결정구조의 특징의 하나인 뒤틀림은 조성비 의 증가에 따라 작아지는 조성의존성 특성을 보였다. Cd1-xCoxGa2Se4 결정의 광흡수 스펙트럼은 Td대칭을 갖는 Co2+이온이 바닥준위 4A2(4F)와 여기준위 4T1(4F) 및 4T1(4P) 에너지 준위사이에서의 전자 전이에 의한 흡수 피크들이 모든 조성 에 대하여 동일하게 600 ∼ 850 nm 파장영역과 1000 ∼ 2000 nm 파장영역에서 관측되었다. 또한 4A2(4F) ⟶ 4T1(4P) 전이에 대응하는 영역에서는 스핀-궤도 결합 효과에 의한 세 개의 분리된 흡수 피크를 관측하였다. 이들 흡수 피크들은 결정장 이론으로부터 잘 설명되었다. 또한 결정장 상수 Dq와 Racah 상수 B는 조성의 변화에 따라 변하는 조성의존성 특성을 보였으며, Racah 상수 B는 모체 결정의 공유결합성에 크게 의존되어 있음을 보였다.
In this work, structural and optical properties of Cd1-xCoxGa2Se4 mixed compound semiconductor based on CdGa2Se4 semiconductor and CoGa2Se4 diluted magnetic semiconductor were investigated in the composition region of 0.0 ≤ ≤ 0.5. The Cd1-xCoxGa2Se4 mixed crystals were prepared by a melt technique using constituent elements(high purity 99.9999 %) in the composition region of 0.0 ≤ ≤ 0.5. The crystal structure was found to be a tetragonal structure of defect cahalcopyrite for a whole composition. The composition dependence of lattice constants showed a linear relation of = 5.7375 - 0.115 and = 10.7775 + 0.125, which satisfies with Vegard's law. It was also shown that the tetragonal distortion depend on a variation of .The optical absorption of Co2+ ions observed in 600 ∼ 850 nm and 1000 ∼ 2000 nm wavelength regions of optical absorption spectra of Cd1-xCoxGa2Se4 crystals was well assigned as the electronic transitions between the ground state 4A2(4F) and the excited states 4T1(4F) and 4T1(4P) of Co2+ ions with a Td symmetry of the host lattice. Also, the triplet absorption structure of the 4A2(4F) ⟶ 4T1(4P) transition was explained along with spin-orbit interaction. The crystal field parameter Dq and the Racah Parameter B varied with a composition . The Racah parameter B was found to be strongly depended on the cavalent bonding of the host crystals.
In this work, structural and optical properties of Cd1-xCoxGa2Se4 mixed compound semiconductor based on CdGa2Se4 semiconductor and CoGa2Se4 diluted magnetic semiconductor were investigated in the composition region of 0.0 ≤ ≤ 0.5. The Cd1-xCoxGa2Se4 mixed crystals were prepared by a melt technique using constituent elements(high purity 99.9999 %) in the composition region of 0.0 ≤ ≤ 0.5. The crystal structure was found to be a tetragonal structure of defect cahalcopyrite for a whole composition. The composition dependence of lattice constants showed a linear relation of = 5.7375 - 0.115 and = 10.7775 + 0.125, which satisfies with Vegard's law. It was also shown that the tetragonal distortion depend on a variation of .The optical absorption of Co2+ ions observed in 600 ∼ 850 nm and 1000 ∼ 2000 nm wavelength regions of optical absorption spectra of Cd1-xCoxGa2Se4 crystals was well assigned as the electronic transitions between the ground state 4A2(4F) and the excited states 4T1(4F) and 4T1(4P) of Co2+ ions with a Td symmetry of the host lattice. Also, the triplet absorption structure of the 4A2(4F) ⟶ 4T1(4P) transition was explained along with spin-orbit interaction. The crystal field parameter Dq and the Racah Parameter B varied with a composition . The Racah parameter B was found to be strongly depended on the cavalent bonding of the host crystals.