缺陷改善效應以及環境應力測試對於GaN p-i-n 紫外光偵測器之影響

Defect reduction and environment stress quality test (ESQT) on GaN p-i-n UV sensor n

劉書史(Su-sir Liu)

指導教授 ： 李佩雯

國立中央大學/資訊電機學院/電機工程學系/博士(2007年)

摘要

在本篇論文中，我們介紹並製作出一系列各種不同改善結構之GaN紫外光偵檢元件。首先我們利用AlGaN/GaN超晶格結構用以改善GaN p-i-n UV-A sensor 元件特性，運用此結構不僅能夠減少長晶薄膜之間的內應力及防止裂痕；同時阻擋並減少螺旋差排向上延伸，元件的磊晶膜品質、載子的遷移率、缺陷密度等均獲得改善，而利用此結構成長的元件不僅暗電流降低；同時紫外光/可見光的對比值均相較於無超晶格結構者為佳。

而在另外一方面，GaN p-i-n UV-A sensor成長於ELOG之上的結構設計，不僅降低了元件螺旋差排之缺陷,有效降低了暗電流的產生；同時亦增加了紫外光波段的響應值以及紫外光/可見光的對比值，利用此結構成長的元件操作特性均相較於無ELOG結構者為佳。研究結果顯示GaN薄膜生長在1度偏角度基板之上有較低的缺陷密度並呈現出較佳的薄膜品質，我們將GaN紫外光偵檢元件結構成長於1度偏角度基板之上發現元件暗電流降低了約二個數量級，紫外光波段的響應值提昇了約20%，因此生長在1度偏角度基板的元件操作特性均相較於無偏角度基板成長元件為佳。

在AlxGa1-xN/GaN元件UV-B波段(310nm)的量測方面,我們採用了p-AlxGa1-xN漸變層的結構設計(Al成分由0.26漸變至0.13)漸變至表層薄的p-GaN磊晶層,則p-GaN之缺陷密度及接觸電阻值均獲得有效降低，元件的暗電流降低了約二個數量級；在此同時光響應值在紫外光波段提昇了約50%，利用AlxGa1-xN漸變層的結構設計製作出來的元件操作特性均相較於無漸變層的傳統結構設計為佳。

我們同時提出了GaN p-i-n UV-A sensor在環境應力測試之下對元件所造成的影響，我們發現暗電流並不隨著溫度增加而提升；然而經過多次的靜態耐電壓測試(ESD)除了會造成元件暗電流的提升；同時降低紫外光波段的響應值及紫外光/可見光的對比值，這是造成元件劣化的主要因素。再者，我們將元件分別經過靜態耐電壓測試
(ESD)、高溫(HT)、以及高溫高濕(HTHH)測試，我們仍然發現靜態耐電壓測試(ESD)對於元件所造成的影響均相較於高溫(HT)以及高溫高濕(HTHH)測試影響來得大；最後我們進行元件的崩潰電壓測試，而在逆向偏壓4500V將會造成元件的失效；而在元件封裝上方面GaN p-i-n UV-A sensor外表批覆矽膠(silicone)以作為保護層，同時設計了PCB電路板作為光訊號處理模組並且搭配一顆9V電池，完成了單一GaN UV single sensor的元件製作。

最後在紫外光陣列(FPA)製作方面，首先我們簡單完成了單一陣列128x1以及5x5 FPA小陣列試製，用以驗證大陣列FPA製作之可行性，最後我們完成了大面積128x128 GaN p-i-n UV FPA並搭配了Indigo Readout Integrated Circuits (ROIC) 顯像讀出電路可以偵測到明顯的紫外光平面UV影像。

關鍵字

光陣列 ； 缺陷 ； 光響應 ； 暗電流

並列摘要

This dissertation presents systematically fabricated GaN p-i-n ultraviolet (UV) photo detectors that have demonstrated improved device structure and superior sensor performance. Studies of the material growth, device fabrication and sensor characterization are described. GaN p-i-n UV-A sensor with a structure of 8-pairs of AlxGa1-xN/GaN superlattices (SLs) grown by MOCVD method, was incorporated into the device. Not only does this device structure eliminate material cracking through strain management, but also significantly decreases the threading dislocation density by acting itself as an effective dislocation filter. The proposed device structure has exhibited excellent epitaxial film qualities, such as improved crystallinity, higher carrier mobility, lower defect levels, and less etching pit density (EPD), and has shown improved performance such as lower dark current, superior response sensitivity in the UV spectrum, and higher UV/visible rejection ratio than those without the SLs structure.

GaN epitaxial material grown using epitaxial lateral overgrowth (ELOG) technique has shown its superiority for GaN p-i-n UV-A sensor application. Due to the minimization of threading dislocations, it is demonstrated that the ELOG technique has reduced the device dark current and increased the responsivity and sharpness of cut-off than that of the traditional design without ELOG design.

GaN layer grown on misorientation angles of a-plane 1o-off-axis sapphire substrate has exhibited excellent film qualities such as enhanced crystallinity, lower defect levels, and less etching pit density. Accordingly, the GaN p-i-n UV-A sensor was first proposed fabricated on 1o off-axis sapphire substrate. The dark current density is decreased by two orders magnitude and the spectrum responsivity is increased 20% than that of traditional on-axis design. A superior device performance can be achieved as device fabricated on 1o off-axis sapphire substrate.
In addition, for applications of AlxGa1-xN/GaN p-i-n UV sensor in UV-B range (310nm), an added a graded AlxGa1-xN (x=0.26

並列關鍵字

Focal plane array ； Defect ； Responsivity ； Dark current

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