半導體兆赫波主被動元件之研究

Abstract

本計畫執行過程中，除了研究表面電將子結構於兆赫波段的特性，並用於開發能影響或調變兆赫波穿透率的被動及主動元件外，我們將研究兆赫波的光源與偵測系統，對象為有雜質摻雜之半導體矽與鍺塊材。透過高功率之CO2 雷射或電場激發樣品，並以有無施加應力為變數，將其運用於分析硼摻雜的矽(Si:B)與鎵摻雜的鍺(Ge:Ga)的發光頻譜，於實驗上做一定性的了解，期能開發半導體兆赫波雷射源。也將以上述兩種材料製作偵測器並致力於提升其反應速率，用於時間解析的頻譜量測，了解兩種材料中載子於低溫下的穩態與非穩態行為。此外，我們提出的一個新的兆赫波電致發光的機制，是利用無能隙半導體受子共振態間發光躍遷來達成。相較於有能隙半導體摻雜，我們預期此機制會有遠超過傳統的發光效率。我們將發展一套理論計算來驗証此機制。利用多體物理並量子統計的技巧，來探討無能隙半導體淺受子能階、生命期與載子在其中的輸運機制。藉由計算不同材料在隨電場、受子濃度下材料增益的變化和共振腔的設計，我們將提出高兆赫波發光效率的半導體元件結構。我們所發展理論計算，不僅僅適用在無能隙半導體，也能用來計算其它能隙不為零的閃鋅礦結構的半導體如矽鍺在摻雜淺受子下的情形。

In the proposal, we will not only investigate the properties of the surface plasma but also the impurity-doped bulk silicon and germanium. For the topic of the surface plasma, we are going to simulate then fabricate the surface-plasmonic structures on metal or semiconductor surfaces to implement terahertz filters and active terahertz modulators. For the topic of the impurity-doped semiconductors, we focus on the following two systems: Si:B and Ge:Ga. By measuring the photo-luminescence (by a CO2 laser) and the electro-luminescence (by applying electric field) spectra of the samples with or without stress condition, we will be able to investigate qualitatively or even quantitatively their physical properties and potential to implement terahertz lasers. During the processes, we will also fabricate terahertz detectors allowing us to perform time-resolved spectra measurement to understand the carrier dynamics after the excitations. In addition, we will propose a new mechanism for terahertz electroluminescence, which is achieved by the carrier transition between the resonant states in a gapless semiconductor. We expect the emission power will be much larger than that in semiconductors with finite gaps. We will develop a theory to verify this mechanism. By using the techniques of many-body physics and quantum statistics, we will calculate shallow acceptor levels, lifetime, and transport properties in an external electric field. By calculating variation of the gain with the electric field (or the acceptor concentration) and designing proper resonators, we will propose a more efficient terahertz laser device. Our theory can not only be applied to the gapless cases, but also all the zinc-blend structure semiconductors with finite gaps like silicon and germanium.