由於鍺錫材料可藉由調變錫濃度以調變能隙，以延長偵測波段；並且和矽同為四族元素，其易整合於矽基板的特性，使得近幾十年被廣泛研究，並應用於紅外波段的光通訊。然而，也由於鍺錫材料擁有較窄能隙的緣故，使得以鍺或鍺錫材料作為主動區地光電二極體被普遍認為有非常高的暗電流，也因此光感測度始終及不上其他三五族作為主動區的近紅外波段光檢測器。
本論文的實驗中，我們製作了三種不同的元件，兩種垂直結構及一種平面式結構的光二極體。垂直結構的光二極體包含了不同厚度的高品質鍺錫材料作為主動層。並對他們進行暗電流、光響應和光檢測度(detectivity)的量測。兩種垂直結構的二極體，其鍺錫材料的厚度為315nm和162nm，並在1550nm的波長和逆向偏壓0.2V的情況下，以正向入射光入射兩種二極體，分別量測到光響應度為0.4A/W和0.01A/W，以及光檢測度分別為9.1×108cm-Hz1/2W-1和1.0×1010cm-Hz1/2W-1。
在暗電流的方面，由實驗結果可以得知，在垂直結構中主要造成暗電流的原因為表面漏電流，而暗電流的居高不下正是造成較低的光檢測度的主要原因，於是我們成功製作了平面式的光二極體試圖降低暗電流。同樣以正向入射的雷射光照射平面式光二極體，我們成功得到了0至-1V之間的較低暗電流，並在1550nm的波長，我們將該平面式光檢測器操作在逆向偏壓0.2V，得到了光響應度為0.04A/W，以及最高的光檢測度，為5.2×1010cm-Hz1/2W-1。

In recent decades, the GeSn material has been investigated and implied to near-infrared photo-communication due to the following two reasons. Firstly, the band gap of such material can be modulated to extend the detection wavelength by incorporating different composition of Sn. Secondly, Ge has good compatibility with Si CMOS processing. However, the narrower band gap of GeSn causes a higher dark current, which results in a lower detectivity than III-V compound photodiode.
In this thesis, we have fabricated three different devices, two of them (N994 and N965) are fabricated into vertical structures and the other one (N990) is fabricated into planar structure. The vertical p-i-n photodiodes with 315nm and 162nm GeSn layer acting as intrinsic regions have been demonstrated. Dark current and photo response were measured, specific detectivity (D*) was then derived by the measured data. Responsivities were measured to be 0.4A/W and 0.01A/W for N994 and N965 at 1550nm, respectively. Detectivities were derived to be 9.1×108cm-Hz1/2W-1 and 1.0×1010cm-Hz1/2W-1 for N994 and N965, respectively.
By measuring dark current density of the vertical photodiodes with different mesa diameters, we find that the main contribution of dark current in a vertical device is surface leakage current, and such high dark current caused a low detectivity. Therefore, we have fabricated the p-i-n photodiode into a planar structure to avoid this phenomenon. The planar photodiode was also measured with a normal incident laser on it. The dark current at the bias voltage between 0 and -1V was reduced. The responsivity was measured to 0.04A/W and the detectivity was measured to 5.2×1010cm-Hz1/2W-1 at 1550nm at a reverse bias voltage of 0.2V.

誌謝 i
中文摘要 ii
ABSTRACT iii
CONTENTS iv
LIST OF FIGURES vii
LIST OF TABLES x
Chapter 1 Introduction 1
1.1 Motivation 1
1.2 Choice of material 2
1.3 Band gap engineering of Ge 3
1.3.1 Tensile strained Ge 3
1.3.2 GeSn alloy 4
1.4 Introduction of GeSn photodetectors 5
Chapter 2 Fabrication equipment and measurement 8
2.1 Fabrication equipment 8
2.1.1 Molecular beam epitaxy (MBE) 8
2.1.2 Mask aligner 9
2.1.3 Reactive-ion etching (RIE) 10
2.1.4 Ion implanter 11
2.1.5 Plasma-enhanced chemical vapor deposition (PECVD) 11
2.1.6 Rapid thermal annealing (RTA) 13
2.1.7 E-beam metal evaporator 14
2.2 Measure setup 15
2.2.1 X-ray diffractometer (XRD) 15
2.2.2 Semiconductor device parameter analyzer 16
2.2.3 Atomic force microscope (AFM) 17
Chapter 3 Fabrication of vertical p-i-n GeSn photodiode 18
3.1 Introduction 18
3.2 Fabrication of N994 18
3.2.1 Sample structure and characteristics 18
3.2.2 Device processing 23
3.3 Fabrication of N965 31
3.3.1 Sample structure and characteristics 31
3.3.2 Device processing of N965 33
3.4 Summary of Chapter 3 34
Chapter 4 Fabrication of planar p-i-n GeSn photodiode 35
4.1 Introduction 35
4.2 Fabrication of N990 35
4.2.1 Sample structure and characteristics 36
4.2.2 Device processing 37
4.3 Summary of Chapter 4 43
Chapter 5 Measurement of p-i-n GeSn photodiode 44
5.1 Introduction 44
5.2 Dark current 44
5.2.1 Vertical p-i-n GeSn photodetector 44
5.2.2 Planar p-i-n GeSn photodetector 47
5.3 Optical measurement 49
5.3.1 Vertical p-i-n GeSn photodiode 49
5.3.2 Planar p-i-n GeSn photodetector 52
5.4 Detectivity 55
Chapter 6 Summary and future work 57
6.1 Summary 57
6.2 Future work 58
REFERENCE 59

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