利用同調兆赫光譜技術研究鎂摻雜氮化銦半導體之兆赫輻射機制

Abstract

本論文我們利用自由空間電光晶體之兆赫光譜技術研究不同載子濃度的c 軸方向鎂摻雜氮化銦薄膜與a 軸方向鎂摻雜氮化銦薄膜的兆赫輻射機制。 我們發現c 軸方向鎂摻雜氮化銦薄膜相較於氮化銦薄膜可產生較強的兆赫輻射功率於載子濃度接近1×1018 cm-3 (nc)。同時亦發現鎂摻雜氮化銦薄膜有反相的兆赫波形，這是由於兆赫輻射機制與載子濃度相依之故。然而，a軸方向鎂摻雜氮化銦薄膜主要的兆赫輻射機制是來自於受激發載子在極化感應電場下有較有效率的半導體介面的幾何耦合輻射效應，與薄膜之載子濃度無關。 利用同調兆赫光譜技術，我們亦發現氮化銦薄膜量測結果與Drude模型的預測相符合，然而鎂摻雜氮化銦薄膜無法利用Drude模型，抑或是運用經修正的Drude-Smith模型得到良好的擬合結果。我們試圖提出c 軸平面鎂摻雜氮化銦薄膜的載子傳輸機制主要是因為電子經載子補償中心而產生的跳躍傳遞過程。

We investigated the terahertz (THz) emission mechanisms of undoped and magnesium doped indium nitride (InN:Mg). THz emission of c-plane and a-plane Mg-doped InN films with different carrier concentrations have been studied by free-space electro-optic sampling terahertz time-domain spectroscopy. We observed the significant THz power enhancement from c-plane InN:Mg with the carrier density near 1×1018 cm-3 (nc), compared to c-plane undoped InN. Depending on the carrier density, the polarity reversal of THz emission was observed for c-plane InN:Mg, indicating THz emission is governed by carrier density-dependent emission mechanisms. For a-plane InN:Mg films, however, nearly equally strong THz emission is observed over a wide variation of carrier density and the dominant THz emission mechanism is due to the acceleration of photo-excited carriers induced the in-plane electric field perpendicular to the axis which increases the geometrical coupling efficiency but not the carrier concentrations. For THz time-domain spectroscopic study, we discovered the experimental result of undoped c-plane InN film can be well-fitted with the Drude model. Moreover, all the results of c-plane InN:Mg films cannot be fitted by Drude or Drude-Smith model. We tentatively propose that the carrier transport in c-plane InN:Mg films to be dominated via electron hopping through these carrier compensation centers.