通過使用線性偏振光的光學激發以及隨後通過線性偏振光致發光的檢測恢復每個谷的種群特徵，證明了SnS中的光物質相互作用，其闡明了對稱性依賴的谷電子學。為了利用這種穀群作為信息存儲或切換設備，設計一種方法來創建可讀輸出受到了顯著的關注。我們首次利用多種配置來展示這種依賴於對稱的谷電子技術的應用，製作多位元元件。這些配置結合了（i）激發波長，（ii）激發偏振方向和（iii）電流（檢測）的方向。激發條件的組合主要是每個能谷的選擇性和電流方向選擇，由於SnS的各向異性傳輸特性來產生多種狀態。我們獲得的差分響應度ΔR高達195A / W，遠高於目前已發表的各向異性光電器件。我們進一步分析了光電流值隨入射激發強度和溫度的變化趨勢，特別是光學激發和去激發時快速和慢速響應時間的分界，並確定了這些時間對光電導和光電效應的貢獻。谷選擇性的部份被識別為由快速過程所貢獻。我們計算出導致響應時間慢和光響應中能谷選擇性的部分損失之缺陷狀態，其活化能為0.12eV至0.17eV，歸因於材料本身自摻雜Sn空位VSn2-，並被視為主要限制因素。應該通過材料合成在未來進行改進。

Light-matter interaction in SnS that elucidates symmetry-dependent valleytronics has recently been demonstrated via optical excitation using linearly polarized light and the subsequent recovery of population characteristics at each valley via the detection of linearly polarized photoluminescence. To utilize such valley population as an information storage or switching device, it is important to devise a method to create a readable output. We show, for the first time, the utilization of such symmetry-dependent valleytronics in a multi-digit device based on various configurations that combines the variations in (i) excitation wavelength, (ii) excitation polarization, and (iii) current (detection) direction. Combinations of excitation conditions allow the selective population of each valley and the choice of current direction utilizes the anisotropic transport property of SnS to generate multiple states defined by the photocurrent values. We obtained a differential responsivity, ΔR, of up to 195A/W, which is much higher than reported anisotropic optoelectronic devices. We further analysed the trends in the photocurrent values with incident excitation intensity and temperature, specifically the demarcation of fast and slow response times upon optical excitation and deexcitation, and identified the contributions of these times to be due to the photoconductive and photogating effects. The valley selective component is identified to be contributed by the fast process. Defect states that lead to the slow response time and partial loss of valley selectivity in the photoresponse are calculated to have an activation energy of 0.12eV to 0.17eV, attributed to the self-doped Sn vacancies, VSn2-, and serve as the main limitation that should be improved via materials synthesis in the future.

Abstract ii
摘要 iv
Acknowledgement v
Table of Content viii
List of Figures xi
List of Table xiii
Chapter 1. Introduction 1
1.1. Background 1
1.2. Reading valley polarization via optoelectronic means. 4
1.3. Motivation 9
Chapter 2. Experimental setup 10
2.1. Methods 12
2.1.1. Sample preparation and characterization 12
2.1.2. Device fabrication 12
2.1.3. Transport measurements 12
2.1.4. Differential responsivity, ΔR, calculations and comparisons 13
2.1.5. Ip-t Curve fitting and calculations 14
2.2. Definition and calculations of figures of merit for device characterized as a photodetector. 15
2.2.1. Specific Detectivity, D*. 15
2.2.2. External quantum efficiency, η. 15
2.2.3. Noise Equivalent Power, NEP. 16
Chapter 3. Result and Discussion 17
3.1. Device characterization 17
3.1.1. Basic material and device characterization. 17
3.1.2. Electric field distribution in SnS based on shape of electrodes 18
3.1.3. Raman spectroscopy 21
3.1.4. Excitation configurations of photocurrent measurements. 25
3.2. Room temperature photocurrent measurements and multi-digit device performance. 27
3.2.1. General power dependence trends. 27
3.2.2. Fast and slow response times. 29
3.2.3. Multi-digit device based on valleytronics. 31
3.2.4. Signal to noise ratio. 33
3.2.5. Non-ideal manifestation of valley selectivity in photoresponse. 35
3.2.6. Optoelectronic responsivity, R. 36
3.2.7. Differential responsivity, ΔR, of anisotropic optoelectronic device. 38
3.2.8. Other optoelectronic figures of merit. 39
3.2.9. Power-dependent Ip and relation to recombination mechanism. 41
3.3. Temperature-dependent trends, key features and transition temperatures. 43
3.3.1. Temperature-dependent Ip. 43
3.3.2. Key temperature-dependent photoresponse features. 44
3.4. Analysis of current contributions and correlation to fundamental mechanisms related to recombination/ trap states. 47
3.4.1. Analysis of Ip-contributing mechanisms. 47
3.4.2. Relating slow rising and decay times. 48
3.4.3. Relating fast rising and decay times. 50
3.4.4. Attributing response times to fundamental mechanisms. 51
3.4.5. Contributions of valley excitation to selectivity in Ip. 52
3.4.6. Quantifying trap states. 55
Chapter 4. Outlook. 57
Chapter 5. Conclusion. 58
References 59

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