| 摘要: | 此論文研究目的為探討銀粒子/氧化銦歐姆接面(Ohmic contact)的光電流特性。我們透過在800 oC高溫氧氣環境下，熱處理不同成分比例的銀銦合金膜，製備出銀粒子/氧化銦結構，並確認其為歐姆接面。然後在不同光子能量的光源照射下來探討其光電流特性。在光強度固定的情況下，光載子的多寡取決於入射光誘發載子的速率及電子電洞對的生命期(Δn = geτr)。因此，本實驗將從這兩方面進行探討。
實驗結果發現，在紫外光照射下，經過氧氣高溫熱處理製備而成的銀粒子/氧化銦結構具有光電流特性。而藉由磁控濺鍍系統製備的氧化銦薄膜卻不具備光電流特性，但在經過氧氣吸附過程序後，即可量測到光電流。因此，其機制被認為是表面氧氣吸附所造成的內建電場，對電子電洞生命期有提升的效果，而使光電流的效應增加。然而，Ag70In30合金膜製備而得的銀粒子/氧化銦歐姆接面，其光電流較經過表面氧氣吸附的氧化銦薄膜高出兩個數量級。此兩者主體皆為氧化銦薄膜，且經過相同時間與溫度的氧氣熱處理。因此，若假設氧氣吸附對於氧化銦薄膜和銀粒子/氧化銦兩者的電子電洞生命期具有相近的增益效應，而銀粒子/氧化銦結構具有較高的光電流，則可對銀粒子能否增加光誘發載子的速率進行探討。而熱電子效應能夠使金屬銀粒子中的電子獲得能量，並且有機會轉移至氧化銦的導帶，提供額外載子，且此效應使得能吸收的光子能量不必高於氧化銦能隙。所以，我們利用光子能量小於氧化銦能隙的藍光、綠光、和紅光做為激發光源，進行光電流量測，且同樣量測到光電流。
根據上述結果，我們發現銀粒子/氧化銦結構在入射光源光子能量高於或低於氧化銦能隙時，皆能誘發光電流。並證實熱電子效應存在銀粒子/氧化銦歐姆接面結構中，且銀粒子能透過此效應提供額外載子至氧化銦的導帶，而量測到光電流。;The aim of this research is to investigate the photocurrent characteristics of Ag particles/In2O3 Ohmic contact. The Ag particles/In2O3 Ohmic contact was fabricated by Ag-In alloy film with different composition heat-treating at 800 oC in oxygen ambience. The contact of Ag and In2O3 is confirmed be Ohmic contact. Photocurrent characteristics of Ag particles/In2O3 composite structure was researched by using illumination light with different photo energies. Since the photo-carrier generation is determined by the optical generation rate and recombination lifetime (Δn = geτr), the discussion will be focused on these two factors.
The results show that under UV-light illumination, the photocurrent of pure In2O3 thin film with the oxygen adsorption could be enhanced. The mechanism has been reported that surface oxygen adsorption would induce a surface build-in electric field and enhance the life-time of excited electron-hole pairs, which would enhance life time. However, the photocurrent of the Ag particles/In2O3 fabricated by oxidized Ag70In30 alloy film is two orders higher than that of the pure In2O3 thin film. Since the matrix of these two samples are both In2O3, and heat-treat in oxygen ambience at same temperature in the same time, We assume that the effect of the surface oxygen adsorption on the recombination lifetime (τr) is similar to the In2O3 thin film heat-treated at 800 oC and the Ag particles/In2O3 composite structure. Then, we discuss that if the optical generation rate (ge) cound be enhanced by Ag particles.
Hot electron effect of Ag particles can transferring the accumulated energy from incident light to electrons by non-radiative decay, and this process would produce highly energetic electrons, which may have sufficient energy to transport to the conduction band of In2O3 and provide excess carriers for In2O3. Therefore, the photo energy is not necessary higher than the band-gap energy of In2O3, and this was checked by illumination light with the photo energy lower that the band-gap energy of In2O3, the blue-light, green-light, and red-light. And, the photocurrent was also measured.
According to the results, photocurrent is observed that no matter the photo energy of incident light is higher or lower than the band-gap energy of In2O3. It can be proved that the hot-electron effect is applied on the Ag particles/In2O3 Ohmic contact structure, which would cause photo-excited electrons of Ag particles transferr to the conduction band of In2O3, and the excess carrier can be measured as photocurrent. |
