本論文我們製作了近紫外光p-i-n偵測器與異質接面光電晶體(Heterojunction phototransistors, HPTs)。兩種光偵測器都是設計了兩種形狀，有方型與長型。異質接面光電晶體是在商業用光二極體(Light-emitting-diode, LED)結構晶圓以矽擴散的方式將最上層一部份的P-AlGaN反轉為N-AlGaN，形成了n-p-i-n結構的光電晶體。反轉得到的二極體做特性量測並比較異質接面光電晶體與p-i-n光偵測器的響應率。
元件在峰值波長384 nm，入射光能量為15.9 μW/cm2時，會有最高的響應率。方形p-i-n光偵測器的元件當逆向偏壓為4.5 V，在峰值的外部量子效率(External quantum efficiency, EQE)為27.6%，對應的響應率為0.085 A/W；而長型p-i-n光偵測器的元件在峰值的外部量子效率為29.1%，對應的響應率為0.09 A/W。方形n-p-i-n光電晶體光偵測器的元件在集極-射極外加偏壓4.5 V(p-i-n接面為逆向偏壓)，在峰值的外部量子效率為30%，對應的響應率為0.093 A/W；而長型n-p-i-n光電晶體光偵測器在峰值的外部量子效率為32.1%，對應的響應率為0.095 A/W。方型與長型的元件結果類似，趨勢一致。
以矽擴散製作的氮化鎵二極體有二極體特性，但因PN接面相當接近表面，空乏區有表面與深層能階。關於光電晶體光偵測器，發現偏壓加到4.5 V，增益仍非常的小，我們認為是因為LED磊晶有一層電子阻擋層(Electron blocking layer, EBL)，使得射極電子不能穿隧(Tunneling)至集極，沒有電流放大效果，外部量子效率比p-i-n結構光偵測器僅略高一點。

In this paper, we fabricated AlGaInN-based near-ultraviolet (UV) p-i-n photodetectors and heterojunction phototransistors (HPTs). They were designed into two shapes which were square and rectangle. The HPTs on a commercial wafer with a light-emitting-diode (LED) epitaxial structure by employing silicon diffusion to convert a part of the top P-AlGaN layer into an N-AlGaN layer, resulting in an n–p–i–n phototransistor structure. We characterized the GaN-based diodes formed by silicon diffusion process and compared the responsivities of the HPTs and the p-i-n photodetectors.
The devices were illuminated using an incident light intensity of 15.9 μW/cm2 at the fixed wavelength of 384 nm at which the responsivity was the highest. The square p-i-n photodetectors with the reverse bias of 4.5 V, the external quantum efficiency (EQE) value at the peak wavelength was 27.6%, corresponding to a responsivity of 0.085 A/W. The rectangular p-i-n photodetectors with the reverse bias of 4.5 V, the EQE value at the peak wavelength was 29.1%, corresponding to a responsivity of 0.09 A/W. The square n-p-i-n phototransistors with the VCE of 4.5 V (p-i-n junction was the reverse bias), the EQE value at the peak wavelength was 30%, corresponding to a responsivity of 0.093 A/W. The rectangular n-p-i-n phototransistors with the VCE of 4.5 V, the EQE value at the peak wavelength was 32.1%, corresponding to a responsivity of 0.095 A/W. The results indicated the square and rectangular devices were similar.
The GaN-based diodes formed by silicon diffusion process due to the PN junction extremely closing to the surface, which resulted in generating the surface level and deep level in the depletion. The HPTs increased the VCE of up to 4.5 V, the EQE value at the peak wavelength was still low. We thought the reason that the electrons in the emitter couldn’t tunnel through the collector was the electron blocking (EBL) in the LED structure. And the HPTs couldn’t amplify the current gain so the EQE value of the HPTs was just a bit higher than that of the p-i-n photodetectors.

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