本論文使用InGaN/GaN多重量子井主動層結構磊晶在圖案化藍寶石基板的晶圓，以表面結構化處理的技術研製p-i-n光偵測器，我們製作兩種不同材料的表面結構處理，分別為：(1)ITO表面粗糙化；以及(2)二維陣列倒置反射杯的氮化鎵表面結構。目的是為了增加短波長在空乏區的光吸收、並增強光擷取的能力以提升光電流與響應率，並且探討比較其元件的光電特性、外部量子效率與響應率。
對於只有ITO表面粗糙化的元件在外加逆向偏壓0 V與1.5 V下，峰值外部量子效率分別為67％和73％，對應的峰值響應率分別為0.21 A/W和0.23 A/W，峰值波長均為388 nm，截止波長約為440 nm，根據定義可得到偵測光對非偵測光的拒斥比可高於1000以上。而有ITO和氮化鎵表面結構處理的元件，在波長為335 nm至365 nm範圍，逆向偏壓為0V時，EQE數值與對應的響應率大概提升50％~85％，然而在峰值響應率的部分約下降14％，意味著蝕刻p型氮化鎵產生許多表面能階與缺陷，而部份入射光被表面能階所吸收。
另一方面，我們也將本論文所設計的元件當作太陽能電池操作，可觀察到有氮化鎵表面結構的元件，隨著氮化鎵蝕刻深度的增加，短路電流密度也隨之提升，但氮化鎵表面經蝕刻後，容易形成表面能階與缺陷，提高暗電流，造成等效並聯電阻(shunt resistance, Rsh)變小，使得Voc數值下降，並減少光電流的收集，進而使得轉換效率不佳。

In this study, we used surface texturing technique to fabricate GaN-based p-i-n photodetectors (PDs) with a commercial epitaxial wafer grown on patterned sapphire substrate (PSS) which has an InGaN/GaN MQW active layer. Two types of surface texturing were performed and compared: (1) a surface-rough indium-tin-oxide (ITO) layer; (2) a surface-textured p-GaN layer consisting of two-dimensional arrays of inverted reflector cups. The goal of surface texturing was to increase short-wavelength light absorption in the depletion region and to increase light trapping for more photocurrent and responsivity. And we characterized and compared the PDs in terms of optical and electrical characteristics, external quantum efficiency (EQE) and responsivity.
The peak EQE values of the sample with a surface-rough ITO layer were as high as 67% and 73% at 0 V and -1.5 V bias, respectively, corresponding to peak responsivity of 0.21 A/W and 0.23 A/W, respectively, at 388-nm wavelength. The cut-off wavelength and the absorption band edge was ~440 nm. The detected/unwanted rejection ratio (defined as the responsivity at peak wavelength to that at a wavelength 10-nm longer than the cutoff wavelength) was higher than 1000. In comparison, we found that in a wavelength range between 335 nm and 365 nm, the EQE value and responsivity for the sample with both ITO and GaN surface texturing were significantly increased by 50%~ 85%, at 0 V bias. Though the peak responsivity was somewhat reduced by ~14% implying some light absorption by the surface states and defects produced at the etched p-GaN surface.
On the other hand, the devices were also operated as solar cells. It was found that the short circuit current density increased with increasing etching depth in GaN. However, the texturing on p-GaN layer caused many surface states and deep-level trapping centers. Thus it increased dark current resulting in a lower shunt resistance, a lower open circuit voltage and less photocurrent collection. Therefore the conversion efficiency was not good.

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