鍺摻雜鎵於電場下之兆赫波放射及吸收頻譜之研究

Abstract

使用傅立葉轉換紅外線頻譜儀(FTIR)的步進掃描振幅調變技術來紀錄在外加脈衝電場下的鍺摻雜鎵樣品於低溫之兆赫波放射頻譜，觀察到受電場激發的電洞從雜質激發態輻射躍遷至雜質最低能階，放出2.01 THz (67.0 cm-1)和2.60 THz (86.7 cm-1)的兆赫波光子，而且我們是第一次量測到鍺摻雜鎵的2.60 THz放射譜線的實驗團隊。 我們也量測鍺摻雜鎵樣品於低溫受外加電流下的吸收頻譜，這些吸收譜線源自電洞從雜質最低能階吸收兆赫波光子至眾雜質激發態，使用了FTIR的步進掃描相位調變技術來得到穩定的吸收譜線，記錄峰值強度對外加電流的變化，觀察到2.04 THz (68.1 cm-1)和2.22 THz (74.1 cm-1)的譜線峰值會隨施加電流增加而降低，我們認為在雜質最低能階的電洞已被電場激發至雜質激發態或共價帶，在200~300 mA大電流的情況下，甚至無法從整個吸收頻譜分辨出微弱的吸收譜線。 使用步進掃描調變技術來量測放射和吸收頻譜，將讓我們能夠分析在不同溫度與電流下雜質能階中的電洞分佈與鬆弛機制。這些實驗成果將有助於兆赫波雷射的實現。

Step-scan amplitude modulation technique on FTIR has been built and applied to the measurement of electroluminescence spectra of Ga-doped germanium at cryogenic temperature. We found emission lines with maxima at ~2.01 THz (67.0 cm-1) and at ~2.60 THz (86.7 cm-1), corresponding to the radiative transitions of holes from the excited impurity states to the ground state of impurity center. The line at 2.60 THz was observed for the first time and investigated. We also measured the intracenter absorption spectra of germanium doped by gallium under external electrical excitation, i.e. electroaborbance spectra, at cryogenic temperature. Step-scan phase modulation technique was used in FTIR for stable peak intensity of absorption lines. The intensity of absorption lines at 2.04 THz (68.1 cm-1) and at 2.22 THz (74.1 cm-1) decreases as the applied current increases. We attribute this effect to the depopulation of the ground state of the impurities and accumulation of the carriers at the high energy excited states or valence band. The intensity of these peals can’t finally be identified as the driving current increases up to 200~300 mA. Using step-scan modulation techniques to measure the emission and absorption spectra enables us to analyze the hole distribution and relaxation mechanisms between impurity states under various temperature and pumping current. These results will be useful for realizing the terahertz laser.