矽摻硼之阻擋雜質能帶紅外線偵測器之研究

Abstract

本論文主要研究平面結構下之矽(摻雜硼)阻擋雜質能帶光偵測器(Si:B block-impurity-band(BIB) photodetector)的特性。有別於傳統磊晶技術，我們使用高純度基板和離子佈植配合黃光技術製作平面結構，用離子佈植製作吸收層而高純度的基版則做為阻擋層。 元件的偵測頻段成功的從357 cm-1向下延伸到250 cm-1。然後我們探討固定電極間距下、不同寬度的阻擋層(樣品A：30 μm和樣品B：10 μm)對元件特性的影響。高電壓下，樣品B元件出現兩個對應到雜質能階的響應峰值。原因可能為在雜質激發態的電洞因撞擊游離而貢獻光電流。樣品A元件則因為阻擋層較厚，所以內建電場較小使得這個現象沒有被觀測到。 產生撞擊游離之前，樣品A元件的響應度較好且雜訊電流較低。產生撞擊游離以後雖使響應度增加但亦提升雜訊電流，而未能大幅度增加BIB元件的表現。由實驗結果可知阻擋層與吸收層厚度的比例將會是影響此類偵測器特性優劣的關鍵之ㄧ。 和傳統的垂直BIB元件作比較，發現響應度的表現差不多，但是在偵測度和雜訊電流的表現上就顯得比較差，或可藉由調整退火製程或使用更高純度之基板來改進此一缺點。

The characteristic of a novel planar Si:B Blocked-Impurity-Band photodetector (BIB photodetector) has been studied in the thesis. We used high-pure substrate, ion-implantation and photolithography to fabricate planar structure. Ion-implantation was used to form the absorbing layer and high-pure substrate served as the blocking layer. The spectral response is successfully extended from 357 cm-1 down to 250 cm-1. Then, we discussed the device characteristic by differing the blocking layer widths, 30 μm (sample A) and 10 μm (sample B), under fixed contact distance. At high bias, two peaks corresponding to the transitions of the isolated impurity levels occur in the response spectrum of sample B. The occurrence of these two peaks could be due to the generation of the free carriers by impact ionization of the excited carriers under high electric field which is not found in sample A. Before the impact ionization, sample A has higher responsivity and slightly lower noise current than those of sample B. The impact process increases not only the responsivity but also the noise current. Therefore, the detectivity of the device shows no great improvement. These results show that the ratio of the blocking layer width to the absorbing layer width is one of the key factors deciding the performances of the BIB photodetectors. Compared with the conventional vertical BIB photodetectors, our devices have comparable value in responsivity. The noise current and detectivity, however, are obviously worse. We might improve the drawbacks by modifying the annealing process or using substrates with higher purity.