近年來光纖通訊蓬勃發展，使得紅外光偵測器逐漸備受矚目。其中，矽基鍺光偵測器不僅有能吸收紅外光的特性，同時還具備低成本及製程易整合之優勢。而其最大的缺點在於矽與鍺間的異質接面缺陷過多，使得暗電流過高造成功率的損耗以及訊號的干擾，因此降低矽基鍺光偵測器之暗電流為目前重要的議題。在本篇研究中，我們將製作不同p-type摻雜層的矽基鍺光偵測器，並探討其對偵測器特性的影響。此外，我們亦將氧化銦錫(ITO)薄膜應用於矽基鍺光偵測器上，希望藉此降低暗電流以提升光偵測器的元件特性。
本研究之矽基鍺光偵測器為p-i-n結構，在利用減壓化學氣象沉積法(RPCVD)將本質鍺層成長於n-type矽基板後，我們利用RPCVD與電子迴旋氣相沉積法(ECRCVD)成長不同結構p-type摻雜層，並探討其對光偵測器特性之影響。結果顯示利用ECRCVD成長p+-Ge摻雜層的光偵測器相較於其他結構，有較高的響應度0.171 A/W，同時暗電流密度維持於0.542 mA/cm2；響應度較高的原因為p-type摻雜層中硼摻雜濃度較高，使得p-i-n結構中有較大的內建電場，進而有效地分離照光後產生的電子電洞對，以形成較大之光電流。
本篇研究亦使用射頻磁控濺鍍法(RF Sputtering)調控各種不同製程參數(氬氣流量、氧氣流量、腔體壓力)成長ITO薄膜於光偵測器上，藉此降低暗電流並同時探討不同特性ITO對於光偵測器的影響，其中光偵測器之暗電流最低可達1.20×10-7 A，暗電流密度為0.048 mA/cm2。而從實驗結果中顯示，添加了ITO層的光偵測器皆有暗電流下降的現象(1~3個數量級)，其原因為載子濃度高於1018~1019 cm-3的ITO薄膜具有填補半導體表面懸掛鍵之特性，因此能夠降低光偵測器之暗電流。

In recent decades, near-infrared-region photodetector has attracted attention gradually with development of fiber-optical communication. Germanium-on-Silicon photodetector not only can detect NIR light but also contain the advantages of low cost and easy integration. However, the defects due to the heterojunction between Si and Ge would increase the dark current which causes power consumption and signal interference so decreasing the dark current of a Ge-on-Si photodetector becomes an important issue. In this study, we fabricated different p-type layer of a photodetector and investigated its effect. In addition, we employed Indium Tin Oxide (ITO) thin film on a photodetector to lower the dark current.
The photodetectors fabricated in this research are p-i-n structure. At the beginning, we used Reduced-Pressure Chemical Vapor Deposition (RPCVD) to deposit intrinsic germanium (i-Ge) on n-type silicon substrate. Then, different kinds of p-type layer were grown by RPCVD and Electron Cyclotron Resonance Chemical Vapor Deposition (ECRCVD). The results revealed that photodetector with p+-Ge layer grown by ECRCVD exhibited higher responsivity of 0.171 A/W than others. The reason is due to the stronger built-in electric field caused by heavier doping concentration in p-type layer.
On the other hand, we grew different characteristic ITO thin film by controlling the process parameters in Radio Frequency (RF) Sputtering system, argon flow, oxygen flow and ambient pressure. Also, we employed these ITO thin films on photodetector to lower the dark current and investigate on the relationship between them. Here, we have demonstrated a Ge-on-Si photodetector with ITO layer and its performance is dark current of 0.12 μA at -3 V bias, dark current density of 0.048 mA/cm2.

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