寬能隙元件與艱困環境下電子元件的物理探討

Abstract

在現代科學任務當中，時常會遭遇到不論是高溫、低溫、高壓等艱困環境，此時若是執行任務的儀器發生故障，將會造成巨大的損失。因此，在這篇論文中，在太陽能電池的部分我將介紹氮化鎵/氮化銦鎵多層量子井太陽能電池在高溫與低溫下的元件表現；以及在金屬氧化物薄膜電晶體部分，我會先最佳化我們製程出的鉿銦鋅氧化薄膜電晶體，再來會將最佳化的薄膜電晶體拿至高能質子轟擊，檢視其抗性。 第一部分是我們將氮化鎵/氮化銦鎵多層量子井太陽能電池升溫至絕對溫度300 K到700 K，我們發現不同於其他種類的太陽能電池溫度上升之後效率下降，氮化鎵/氮化銦鎵多層量子井太陽能電池當溫度上升之後效率持續增加至650 K，因此我們從材料方面以及結構方面來探究其原因。以材料方面來說，因為氮化鎵、氮化銦鎵皆屬寬能係材料，寬能係材料的太陽能電池在升溫的時候，開路電壓下降的較慢，效率也就下降的較慢，此外有研究指出，P型氮化鎵在高溫時，導電度會降低，與金屬的接觸電阻也會降低，由我們對於填滿因子及串聯電阻的研究就能驗證此事。再來是結構方面，量子井結構對於太陽能電池在高溫下會有特別的作用，銦波動對高溫效率也有顯著的影響。最後是回復力方面，熱崩潰發生在材料中就會造成材料毀損，氮化鎵的熱導性很好，熱導性好的材料其的熱崩潰所需要的場就會越大，也就是越難熱崩潰，因此我們研究也發現氮化鎵的太陽能電池在700 K之後也能保持正常的操作效率。 第二部分我首先先製程最佳化的Hafnium indium zinc oxide thin film transistor，經由不同的鍍膜條件與不同的元件幾何長度嘗試出最好元件表現的薄膜電晶體。再來，我將這個最佳化的薄膜電晶體拿去做質子轟擊，發現在dose量為 1013 cm-2時，元件表現變差，原因應該為介面與通道缺陷增加；在dose量為 1015 cm-2卻產生的動態退火現象，元件特性稍微回到一開始的表現。最後我們分析當我們將不同Hf 濃度做質子轟擊時，高濃度的Hf可以幫做薄膜對抗質子轟擊，增加薄膜電晶體的穩定度。

InGaN/GaN MQW solar cells have much better performance than other kinds of solar cells due to larger Jsc increasing rate, smaller Voc decay rate and the enhancement of FF with temperature. The reason can be investigated through material and structure viewpoints. Wide bandgap makes temperature induced recombination rate smaller and then Voc degradation rate is reduced. FF of the device enhances dramatically due to the improvement in material conductivity and reduction of contact resistance with increasing temperature. MQW structure and suffered from indium fluctuation indeed have larger enhancement of Jsc in high temperature. Considering the recovery, GaN-based MQW solar cells don’t suffer from thermal breakdown from 300 K to 700 K and demonstrate the excellent stability in harsh environments such as extreme temperatures. The rise of space program has stimulated the demand in developing technology for outer space use. Radiation damage and gigantic variation in temperature are major issues while applying electronic devices in space mission. Proton bombardment on electronics causes the degradation of the material conductivity due to the formation of additional electron traps. In addition, when increasing temperature, oxygen atoms are thermally excited which leave their original sites and then causes vacancies. In this study, we investigate the method to engineer the electrical properties of InZnO-based transistors (IZO TFTs) and explore the way to stabilize them as operated in harsh environment. Generally, an effective approach to stabilize the IZO TFT is to implant metal cations such as Gallium (Ga3+), Magnesium (Mg2+), Hafnium (Hf4+), Tin (Sn4+) and Zirconium (Zr4+). We show that by modifying the Hf ratio the electrical properties of InZnO-based thin film transistors, i.e. HIZO TFT (Fig. 1), can be tuned. Moreover, subthreshold swing (SS) degradation and a negative threshold voltage (Vth) shift due to proton bombardment and high temperature are observed in the transfer curves; however, the TFTs with appropriate addition of Hf shows better stability and performance. It shows that theaddition of Hf ions can suppress the formation of oxygen vacancy and stabilize the film's atomic structure as well as electrical properties. As a result, reducing oxygen vacancy generation not only restrains SS degradation but also significantly improves the bias stress stability in HIZO TFTs operated in harsh environment.