硫化氫是一種無色、易燃、劇毒、臭雞蛋味的氣體。由於它的毒性，在一些工作場所需要安裝硫化氫感測器，來偵測環境中硫化氫的含量。為符合相關國家的法規，目前市面上的硫化氫感測器的閥值大多數為10 ppm,且偵測原理一般採用金屬氧化物，比如氧化銅或者氧化錫,工作溫度從室溫到數百攝氏度，偵測濃度從10 ppb到100 ppm不等。從上世紀八十年代開始，人們開始研究使用Schottky diode來偵測氣體，在氫氣偵測方面，目前已有很多實驗資料及成果，但仍沒有硫化氫的研究。此論文中硫化氫感測器使用氧化鋁為基板，在其上鍍有一層厚約1.5μm的氮化鎵膜作為半導體。氮化鎵之上共有四層結構，形成肖特基接觸和歐姆接觸，並使用鉑為催化金屬。在高於180攝氏度的環境中,當硫化氫氣體接觸到鉑後裂解為氫原子,進入肖特基接觸介面,降低肖特基勢壘,改變該感測器電阻值。該感測器靈敏度很高，可測低至50 ppb的硫化氫。當濃度高於1 ppm時，偵測反應快，反應時間在10 s內。

Hydrogen sulfide is colorless, flammable and highly toxic gas with typical rotten egg smell. Hydrogen sulfide often results from the bacterial breakdown of organic matters. Because of its toxicity, many hydrogen sulfide personal safety gas detectors are set to alarm at 10 ppm. Most of hydrogen sulfide sensors are made of metal oxide, especially CuO and SnO, and work from room temperature to several hundred Celsius degree. The sensing limit can vary from 10 ppb to 100 ppm. A number of Schottky diodes have been fabricated as gas sensors with catalytic metals since 1980s. Although there are many researches studying in the hydrogen sensing characteristics using Schottky diode, there are still no paper investigating hydrogen sulfide sensing. According to previous researches, Pt/GaN Schottky diode is sensitive to hydrogen and ammonia. Because of its sensing mechanism, it can also be sensitive to hydrogen sulfide. The Ga-face GaN was grown on sapphire substrate by a metal-organic chemical vapor deposition (MOCVD) system. The main structure on the substrate is a Schottky contact, which is formed by Pt and GaN and separated from an Ohmic contact. With present Pt/GaN Schottky diode, we can detect hydrogen sulfide down to 50ppb and get a calibration curve in different concentration. Additionally, this device shows fast response time of around 10 seconds when the concentration of hydrogen sulfide is higher than 1 ppm.

Contents
Chapter 1 Introduction 1
1.1 Hydrogen sulfide 1
1.2 Motivation 3
Chapter 2 Literature Review 5
2.1 Electronic nose 5
2.2 Schottky diode as gas sensor 6
2.3 Hydrogen sulfide sensors and comparison 7
Chapter 3 Experimental 11
3.1 Fabrication of Schottky diode 11
3.1.1 Substrate 12
3.1.2 First layer: Ohmic contact 12
3.1.2 Si3N4 deposition 13
3.1.3 Platinum deposition 14
3.1.4 Final metal deposition 15
3.2 Contact resistance measurement 15
3.3 Sensor measurement 17
Chapter 4 Results and Disscussion 20
4.1 Basic Schottky diode property measurement 20
4.2 Real-time detection 22
4.3 Detection limit 25
4.4 Calibration Curve 25
4.5 H2S poisoning 27
Chapter 5 Application and future work 29
5.1 H2S detector used in industrial workplace 29
5.2 Application in food spoilage detection 29
5.3 Future work: Better design for commercial product 32
Reference 33

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