AgGaS2單晶生長與光學性質之研究

Abstract

本研究是以垂直布氏長晶法在不同溫度梯度下生長 AgGaS2 單晶。在所生長之單晶內部觀察到影響晶體穿透率的析出物，經 Ag2S在 900℃ 下8天的熱處理，析出物明顯的消除具晶體的穿透率亦顯著提昇。此外藉由各式量測，得到所長晶體的穿透範圍為 0.48→13μm；有效倍頻係數在1.064μm為0.77pm/V；室溫下能隙為2.682eV。 由於晶體生長的降溫過程中，晶體 C 軸熱縮冷漲現象產生的應力造成晶體內部雙晶的形成。為了消除這應力，建議使用 C 軸方向的晶體作為長晶晶種。於是採用全光學的方法取代傳統 X-ray 方法測定晶體光軸，其準確度可達一度以內。

In this study, the Silver thiogallate (AgGaS2) single crystals were grown by Vertical Bridgman method under different temperature gradients. In the as-grown crystals, we observe lots of precipates exited in the crystals which dominate the transmittance of light. After heat treatment with 0.5% Ag2S at 900℃ for 8 days, these precipates have been reduced significantly and the transmission of light in crystals have been apparently improved. By using various measurements, we obtain that the transmission range is 0.48→13 μm; the effective SHG coefficient at 1.064μm is 0.77 pm/V; and the energy band-gap at room temperature is 2.682 eV. Due to the stress resulting from thermal expansion in the crystals during the cooling process, a few twins were generated. In order to ease this stress during cooling, we suggest to use a c-axis oriented seeded crystal for the crystal growth. Instead of using conventional X-ray method, we develop a full optical technique to find the crystal's c-axis, and its axis direction can be precisely determined to less than 1 degree.