本文採用一種方式來製備低串接電阻、高響應度的光通訊用檢光器。以砷化銦鎵作成p-i-n結構(p-InP / i-InGaAs / n-InP)的檢光器已廣泛被使用在一般光通訊用途，尤其是元件直徑250~300um的大尺寸MPD( Monitor Photo-detector)。若是元件直徑小於90um小尺寸PIN的寬頻及高速元件，則因p-InP與金屬電極的串聯電阻較高很少被應用。為了讓小尺寸PIN的砷化銦鎵的檢光器也能有較小的串聯電阻，本文用有機金屬汽相磊晶系統研製一系列磷砷化銦鎵晶膜，並添加在基本的p-i-n結構檢光器上，嘗試取得適合的材料組成以改善檢光器的元件特性。
首先使用有機金屬汽相磊晶系統進行磊晶條件測試，採用高溫裂解方式並利用鋁原子容易吸附氧氣的特性，純化反應環境，使得吸光層擁有低背景濃度（8.31×1013cm-3）與高電子移動率（13400cm2/v-s），並藉由材料量測以確定成長晶膜品質的優劣。為了讓晶膜能與磷化銦基板有較少的缺陷，我們調整材料的元素組成比例使得砷化銦鎵與磷砷化銦鎵和磷化銦基板的晶格不匹配度控制在150ppm以內。
有了品質良好的磊晶片作為基礎後，我們先建構出沒有和金屬銜接的半導體接觸層的基本砷化銦鎵p-i-n檢光器。雖然基本砷化銦鎵p-i-n檢光器沒有加入半導體接觸層，可是利用降低受光區的尺寸到65um以下時，我們可以獲得較低的暗電流和電容；以1310nm為固定入射光源時，也能獲得0.884A/W的光響應度。可惜的是因為沒有加入半導體接觸層，因此要到達1mA的順向電壓也隨著受光區尺寸的逐漸縮小而不斷增大，以此算出整個串聯電阻幾乎高達82.6歐姆；因為存在較高串聯電組的這個問題，沒有半導體接觸層的基本砷化銦鎵p-i-n檢光器不適合操作在高速元件。
受限於p型磷化銦蓋光層的材料特性，摻雜的濃度一直很難提升到5×1018cm-3以上。為了將砷化銦鎵p-i-n檢光器應用在光纖通訊系統的波段1310nm（光色散最小）及1550nm（光損失最低），中空環型的 In0.53Ga0.47As 結構被加在p型磷化銦蓋光層上當作與金屬之間的接觸層。雖然In0.53Ga0.47As相較於各種與磷化銦基板晶格匹配的材料相比有著更低的能隙和更高的p型摻雜濃度，可是In0.53Ga0.47As會吸收波長較其短的光源，為了讓主要感測波段進入吸光層，因此必須做成中空的環型結構。此舉將增加製程的複雜度，除了容易降低良率以外也會增加製程上的成本。為了簡化這道製程步驟，我們嘗試用其他物質吸收波長小於1310nm的材料作為蓋光層與金屬之間的接觸層。
為了做到高濃度的p型摻雜以達成較低的串接電組，本文嘗試了幾種不同能隙的磷砷化銦鎵材料（對應的物質波長在0.92um到1.3um之間），搭配不同濃度的擴散方式，探討對元件的影響與差異。實驗結果顯示：鋅原子在In0.784Ga0.216As0.474P0.526 (PL~1.225um)材料中，橫向擴散的速度遠比縱向擴散來的快；而且砷原子成分愈多（能隙愈小，物質波長愈長時）時，鋅原子擴散的速度愈快，p型摻雜的濃度也愈高。然而在磷砷化銦鎵材料中鋅原子的快速的橫向擴散是造成漏電流的主要因素。倘若降低p型摻雜的濃度，是可以降低些許的暗電流。經過實驗的證明，In0.784Ga0.216As0.474P0.526 (PL~1.225um)這種半導體接觸層還是需要做成中空環型的結構才能避免過高的暗電流產生。
最後我們採用微量矽摻雜的n型In0.8929Gax0.1071As0.2346P0.7654半導體(材料能隙為1.18eV，意即 PL~1050nm)作為半導體接觸層，在無須做中空環型結構的製程下即可降低串聯電阻與獲得高的光響應度。在受光區直徑為65um時，以1310nm為固定入射光源時，能獲得1.03A/W的光響應。和基本只用p型磷化銦做蓋光層的檢光器相比，加入波長1050nm的In0.8929Gax0.1071As0.2346P0.7654半導體接觸層後，在1mA的順向電壓已經從1.38V降到0.6V，電阻值也從82.6歐姆降到21.7歐姆。當受光區直徑降到90um~45um時，隨著受光面積的減小，電容值也會不斷的跟著降低到1.4pF~1.2pF。

In this thesis, some low series resistance p-i-n photodiodes have been successfully fabricated and investigated by metal organic chemical vapor deposition (MOCVD). At present In0.53Ga0.47As p-i-n photodiodes have been applied in the fiber-optical communication, especially in large dimension MPD (Monitor Photo-Detector). On the other hand, small aperture photo-detectors have made remarkable progress in high speed and bandwidth devices. In order to achieve a low RC constant detector and keep a simple fabrication process, we propose the p-i-n PD with suitable In1-xGaxAsyP1-y contact layer.
Among the several available epitaxial techniques, MOCVD epitaxial technique has been widely studied for InP based compound semiconductor. A series of measurements, including double-crystal X-Ray diffraction (DCXRD), photoluminescence (PL), Hall measurement and electro- chemical capacitance-voltage (ECV) profile are used to check material quality. For In0.53Ga0.47As absorption layer, a very low background concentration 8.31×1013cm-3 and good electron mobility 1.3×104cm2/v-s are achieved. Furthermore, lattice mismatch of epi-layer is well controlled within ± 150ppm.
First, a fundamental In0.53Ga0.47As p-i-n photodiode without contact layer is fabricated. The dark current decreases with decreasing incident light absorption aperture area. But the forward voltage increases with decreasing incident light absorption aperture diameter. On the other hand, there is large resistance at small aperture diameter of fundamental In0.53Ga0.47As p-i-n photodiode without contact layer. By decreasing the aperture diameter of the p-i-n photodiode, the capacitance is reduced apparently. But the device without contact layer can’t still satisfy high speed performance due to the large series contact resistance issue.
The high doping concentration of the p-InP cap layer above 5×1018cm-3 is difficult to achieve. For 1310nm and 1550nm application of the fiber-optical communication, In0.53Ga0.47As ternary contact ring is added on cap p-InP layer. Although In0.53Ga0.47As contact layer has lower energy gap and higher p-type doping concentration than the In1-xGaxAsyP1-y quaternary material. But the incident wavelength below 1650nm will be absorbed by In0.53Ga0.47As contact layer, the In0.53Ga0.47As ternary contact ring process is necessary for high response application. However the contact ring process will add the device complication and process cost. In this thesis, we propose a series of transparent In1-xGaxAsyP1-y contact layer (λ<1.31um) to simplify the device process.
In order to attain high doping concentration and low series resistance, a In1-xGaxAsyP1-y contact layer is inserted between the p-InP cap and metal. The small aperture In0.53Ga0.47As p-i-n photodiodes with In1-xGaxAsyP1-y contact layer are demonstrated with low series resistance and low junction capacitance. As the wavelength of latticed-matched In1-xGaxAsyP1-y material increases, the zinc doping concentration and diffusion speed are higher. The fast lateral diffusion of In1-xGaxAsyP1-y layer will result high large dark current due to the lateral leakage current. Low zinc diffusion concentration improves little dark current a little. Fast lateral zinc diffusion in In0.784Ga0.216As0.474P0.526 layer (PL~1.225um) layer causes large leakage current. In0.784Ga0.216As0.474P0.526 layer (PL~1.225um) contact ring process is still necessary for low dark current.
Finally, a small aperture In0.53Ga0.47As p-i-n PD with an In0.8929Gax0.1071As0.2346P0.7654 (energy gap=1.18eV, PL wavelength=1050nm) contact layer have been fabricated and demonstrated to achieve low contact resistance and good responsivity without contact ring process. The In0.784Ga0.216As0.474P0.526 layer (energy gap=1.012eV, PL~1.225um) and In0.8929Gax0.1071As0.2346P0.7654 (energy gap=1.18eV, PL wavelength=1050nm) are studied for contact layers. The doping concentrations we can achieve are from 1×1019cm-3 to 3×1018cm-3. The dark current of In0.8929Gax0.1071As0.2346P0.7654 (energy gap=1.18eV, PL wavelength=1050nm) contact layer is significantly lower than In0.784Ga0.216As0.474P0.526 layer (energy gap=1.012eV, PL~1.225um). As compared with p-InP contact layer, the In0.8929Gax0.1071As0.2346P0.7654 (energy gap=1.18eV, PL wavelength=1050nm) layers also reduce the forward bias voltage and the series resistance of photo-detector. Experimentally, the capacitance also decreases with the smaller aperture size. The PD with In0.8929Gax0.1071As0.2346P0.7654 (Eg=1.18eV, PL ~1050nm) contact layer has been successfully demonstrated to achieve low contact resistance without contact ring process.

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