我們比較 SI-GaAs 與 SI-InP 之 THz emitter，發現 SI-InP THz emitter 能承受較高的外加偏壓，較符合我們的需求；且針對外加偏 壓、激發光能量大小、激發光點聚焦與位置等參數，與其激發出的 THz 輻射大小作一比較；於系統上加裝一溫度控制系統，提供 THz emitter 在一更穩定的環境下運作；比較不同電極形狀與平行板電極間 隙大小對THz 輻射的影響；利用 THz-TDS 的技術得到半絕緣磷化銦 在THz 波段的頻率響應；另外發現我們的系統在激發光 45°入射時有 最強之THz 訊號。
將目前的兆赫輻射系統和量測結果與學長完成之系統和量測結 果作比較，後者採用之THz emitter為SI-GaAs平行板電極，電極間隙 500μm，外加偏壓 200V時的訊號最穩定，其兆赫波電場分布如圖 4-1(a) 所示。目前最佳的結果，使用的THz emitter為SI-InP平行板電極，電 極間隙 500μm，外加偏壓達 400V時、其兆赫電場分布如圖 4-1(b)所 示，由圖 4-2 顯示後者兆赫波電場約增加 7.5 倍，兆赫波功率強度增 加(7.5)2倍。且訊雜比提高約 100 倍（圖 4-3、圖 4-4）。
我們雖已初步達成目標，使THz 輻射系統使其更有效率、穩定。
然而系統尚有許多改善的空間。在材料的選擇上，低溫成長砷化鎵
（LTG GaAs）是目前極熱門的材料，利用分子束磊晶法成長砷化鎵 時，控制基板溫度於200℃左右（正常之基板溫度約為 600℃）。利用 這方法長出來的砷化鎵含有較多的砷及大量的缺陷，因此它具有高電 阻性、短光激發載子生命期及高崩潰電場，非常適合拿用應用於兆赫 輻射發射元件[26]；電極形狀的設計相信仍大有可為，也有研究群朝 陣列式電極形狀做努力[27]；可以設計一真空腔利用液態氮來降低 THz emitter 的溫度，預期輻射效率會更高；而平行板電極間隙大小，
雖然實驗結果400μm 較 500μm 輻射效率好，但因半導體基板的條件 不同而未能作一完整比較。激發光入射角的影響為本論文最遺憾之 處，當激發光以布魯斯特角入射時會產生最大的光電流，理論上也應 當有最強的兆赫輻射，期許未來可以更完整的作一系列比較，得知 THz emitter 操作條件最佳化。
-1 0 1 2 -150
-100 -50 0 50 100 150
EO signal(arb.units)
Delay Time(ps)
(a) SI-InP Bias:400V (b) SI-GaAs Bias:200V
圖4-1：現在與過去得到的 THz 訊號比較。
0 50 100 150 200 250
EO signalpeak-peak(arb.units)
now before
圖4-2：現在與過去得到的 THz 訊號大小示意圖。
0 2 4 6 8 10 12 14 16 18 20
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