非均勻量子井紅外線偵測器之研究

Abstract

摘 要 非均勻量子井組成是將傳統相同的多重量子井改變成具有不同位能障壁寬度及雜質濃度的量子井組合，本篇論文之目的在對n型非均勻量子井紅外線偵測器(non-nuniform QWIP)的特性進行瞭解並針對其缺點進行改善。我們以束縛態至連續態、束縛態至準束縛態與束縛態至束縛態三種不同的躍遷形式來瞭解其各項物理特性。在暗電流方面，三種躍遷的非均勻結構均能有效的抑制暗電流（降低3-7倍），而光響應的部份，在束縛態至連續態躍遷方面，非均勻結構比一般傳統結構大了一倍，在束縛態至準束縛態與束縛態至束縛態方面，光響應比一般結構小，但是因為暗電流的下降所以元件的偵測度並沒有下降，而且效地提升了元件的背景限制溫度。我們也透過中波段的研究，更深刻的知道非均勻量子井紅外線偵測器的操作機制與使用限制。此外，我們以震盪式的參雜與位能障壁寬度（非均勻結構的變形Modified Non-uniform QWIP）來取代部份的非均勻結構，實驗發現暗電流可降低三倍左右，而同時其光響應幾乎不受到影響，這提升了元件的背景限制溫度至77K，偵測度也提昇1.5倍。我們也利用元件的電場分布計算，成功的解釋非均勻結構(的變形)的操作原理與溫度效應。

Abstract The conventional uniform structure is replaced by a non-uniform structure with different doping concentration and barrier width for the wells. In this dissertation, we try to realize the characteristics of the non-uniform QWIP and solve its problem about high dark current. We fabricated the samples of three types of transition: bound to continuum, bound to quasi-bound and bound to bound to understand their physical properties. In studies of dark current, all transition types of non-uniform structure can reduce the dark current (about 3 to7 times lower than conventional QWIP). For the photo-response, the bound to continuum non-uniform structure has higher responsivity than uniform one by two times at -1V, but the lower responsivity we got from the other two types of transition. Due to the reduction of dark current, the detectivity of all non-uniform devices is not lower than that of conventional QWIPs and the BLIP temperature is raised, even though the low responsivity in bound to quasi-bound and bound to bound samples. Under investigating the mid-infrared QWIP, we can deeply know the mechanism and the limitation of non-uniform QWIPs. Besides, without affecting the responsivity, the dark current can be reduced by three times as the some part of non-uniform structure is changed by the high and low doping concentration (narrow and wide barrier thickness). We call this device "Modified Non-uniform QWIP MNQWIP". The BLIP temperature of MNQWIP is up to 77K and its detectivity is 1.5 times higher than that of non-uniform structure. By using the self-consistent model to evaluate the potential profile of (modified) non-uniform QWIPs, we successfully explain their characteristics and the behavior as temperature varying. 中文摘要…………………………………………………………………………….. i 英文摘要…………………………………………………………………………….. ii 致謝………………………………………………………………………………….. iv 圖目錄……………………………………………………………………………….. v 第一章 簡介 ( Introduction ) ………………………………..……………………… 1 1.1 黑體輻射 (Blackbody Radiation)…………………………………. 1 1.2紅外線偵測器(Infrared detector)……….……………………….. 3 1.3 量子井紅外線偵測器的發展歷史(History)……………………….. 5 1.4 量子井紅外線偵測器的應用-焦面陣列(Focal Plane Array:FPA). 8 1.5 論文組織………………………………………………………………. 10 第二章 原理 ( Fundamental Theory )……………………………………………….. 11 2.1 次能階的吸收(Intersubband Absorption)……………………….. 11 2.2 暗電流(Dark current)………………………………………………. 13 2.3 光響應(Responsivity)………………………………………………. 14 2.4 雜訊(Noise)…………………………………………………………… 15 2.5 偵測度(Detectivity)……………………………………………….. 17 2.6 自我一致計算方法(Self-consistent Model)…………………….. 18 第三章 製程與量測( Process and Measurement ) …………………………………. . 22 3.1製程步驟………………………………………………………………… 22 3.2量測原理………………………………………………………………… 25 第四章 非均勻量子井紅外線偵測器. ( Non-uniform QWIPs ) …………………….. 29 4.1非均勻結構與一般結構量子井紅外線偵測器的比較………………. 4.1-1束縛態至連續態躍遷(Bound to Continuum Transition)…… 30 31 4.1-2 束縛態至準束縛態躍遷(Bound to Quasi-bound Transition) 34 4.1-3 束縛態至束縛態躍遷(Bound to Bound Transition)……….. 37 4.2 中波段（3-5μm）非均勻結構的特性……………………………… 40 4.3 溫度效應 (Temperature Effect)………………………………..……… 41 4. 4 非均勻結構三種躍遷與中波段的比較……………………………… 42 4.5總結(Summary )………………………………………………………... 44 第五章 結論 ( Conclusion ) …………………………………………… ………… 71 參考文獻…………………………………………………………………………….. 73