中 文 摘 要

本論文係使用有機原子層磊晶法首次在150℃低溫及30 Torr低壓下分別成長硒化鋅、硫硒化鋅及硒化鋅-硫化鋅應力層量子井結構於n型 (100) 矽基板上，且以甲基化鋅、硫化氫及硒化氫為反應物。原子層磊晶法是著名適合於成長超薄的半導體方法，因它能精確控制單一原子層之薄膜沈積厚度、低溫且均勻成長在大面積上，藉著自我限制反應機制由氣體分子之供應時序交替導入在基板表面上達成成長。理想的每週期單一原子層厚度可在寬範圍的參數：基板溫度、莫耳流率及反應物通入之時間而獲得。由X-射線繞射光譜可知硒化鋅為 (400) 面之單晶。在原子層磊晶成長溫度150 - 200 ºC下，硒化鋅薄膜具有平滑如鏡之表面結構。低溫 (7K) 時，硒化鋅薄膜在光激光譜 (PL) 可得其近能帶隙於2.8 eV處發光，其波峰之半高寬只有36 meV。其肖特基二極體在常溫時具有優越的電特性如：超過40伏特的高崩潰電壓，以及0.6 - 0.8伏特間的低切入電壓。以所獲得的ZnSe/Si磊晶薄膜性質，此材料可適用於藍光發光二極體或應用於直流式薄膜電激發光顯示器。
硫硒化鋅薄膜，在硫元素達百分之九十三時，晶格常數可和矽基板相匹配；可獲得較佳且均勻的表面結構和較窄的X - 射線繞射光譜半高寬。同時，在ZnSxSe1-x的能隙可由光激光譜 (PL) 得到並發現在ZnS0.93Se0.07在一較強的近能帶隙光譜。室溫下ZnS0.93Se0.07薄膜最大霍耳移動率為347 cm2/v - sec。其肖特基二極體具有優越的特性如：20伏特逆偏壓時，其漏電流可低至45 nA，超過40伏特的高崩潰電壓，和0.68伏特的低切入電壓。結果顯示出良好的ZnS0.93Se0.07/Si晶格匹配是由於磊晶層介面間缺陷的減少所造成。
由於硒化鋅和硫化鋅具有高失配率，在150 ºC低溫成長應力層量子井結構時，可消除三維成長方式。良好的結晶品質可在X - 射線繞射光譜中觀察到。由二次離子質譜 (SIMS) 中，觀察到超晶格層中原子波動變化分佈，可確知該結構已形成。由實驗知測試樣品至少具有25週期厚度時，方可在室溫下呈現出強藍光，並且幾乎測不出由深能階的發光帶。單一量子井之光激光譜 (PL) 與理論計算相當一致。隨著硒化鋅井層的厚度增加，發光波峰趨向於低能區，證明具有量子效應。由應力層量子井結構製作的肖特基二極體，可改進電流-電壓特性，可獲得較低之切入電壓：80 - 150 mV。這些電特性很適合應用於直流型電激發光薄膜元件之製作。

Abstract

High quality epitaxial growth of undoped ZnSe, ZnSxSe1-x and ZnSe-ZnS strained quantum well structures were successfully grown on n-type (100)-oriented silicon substrates at 150 ºC in a horizontal cold-wall quartz reactor by low-pressure metalorganic atomic layer epitaxy (MOALE) at a pressure of 30 Torr for the first time. Dimethylzinc [Zn(CH3)2, DMZn], hydrogen selenide (H2Se) and hydrogen sulfur (H2S) were used as the reactants. ALE is a suitable technique for the growth of ultra thin semiconductors because it provides accuracy monolayer control of the deposited film thickness, low growth temperature and uniform growth over a large area by its“ self-limiting mechanism ”via supplying source materials in a flow pulse sequences alternatively over the substrate. Idea one monolayer per cycle was obtained in wide range of parameters such as substrate temperatures, mole flow rate and pulse duration of reactants. From X-ray diffraction pattern, (400)-oriental single crystal epilayers of ZnSe are evidenced. The surface morphologies of ZnSe in the ALE temperature region 150 - 200 ℃, extensively smooth and mirror-like surface were obtained. PL spectra of ZnSe epilayer is dominated by the strong near-band-edge at 2.8 eV with FWHM of 36 meV. Schottky diodes were fabricated from the undoped ZnSe layer and the electrical properties were measured at room temperature. From the current-voltage (I-V) characteristics, a high reverse breakdown voltage (>40 V) and an excellent low cut-in voltage of 0.6 - 0.8 V were obtained. On the basis of the observed ZnSe/Si epitaxial film properties, the material is suitable for fabrication of ZnSe-based blue light emitting diodes and for application in direct-current thin-film electroluminescence.
The lattice of the ZnSxSe1-x layer with a sulfur content around 93% was found to have the best match to the Si substrate, as confirmed by the good layer thickness, uniformity, surface morphology and narrow linewidth of the X-ray diffraction rocking curve with a minimal FWHM of about 0.16 degree. In addition, strong near-band-edge and weak deep-level emissions in the longer wavelength region dominate PL spectra of the ZnS0.93Se0.07 epilayer at 300K. With respect to Schottky diodes, Au/n-ZnS0.93Se0.07/Al, has a high breakdown voltage, over 40 V at 400 nA and a low cut-in voltage of 0.68 V. The highest Hall mobility of the ZnS0.93Se0.07 is 347 cm2/v-sec. These results indicate a good lattice-match of ZnS0.93Se0.07/Si as a result of low numbers of interface and epitaxial layer defects.
The lower temperature of ZnSe-ZnS strained quantum well structures, 150 ºC would be lowed enough to eliminate 3-D growth related to the lattice mismatch between ZnSe and ZnS. A good epitaxy and crystallinity was carried out by X-ray diffraction. The formation of the strained quantum well structure is evident from the periodic behavior of each fluctuation profile by SIMS. At least 25 periodic thickness of the ALE growth samples shows a strong blue emissions and nearly neglects the deep-level emission at room temperature. The phenomenon of quantum size effects and the “ blue-shift ” was evidenced as the well width increases. The results of the PL measurements were found to correlate well with the theoretical one, parabolic well-strain mode. Schottky diodes were fabricated from the Au/ZnSe-ZnS SMQW/n-Si/Al, a high reverse breakdown voltage over 40 (at 20 µA) and an extremely low cut-in voltage of 80 - 120 mV were obtained. The I-V characteristics of the heterojunction are more suitable for the fabrication of the direct-current thin film electroluminescent (EL) device.

Table of Contents

Abstract.................................................................................................................................. i
Table of Contents..............................................................................................................… v
List of Figures..................................................................................................................... viii
List of Tables....................................................................................................................... xii

Chapter One Introduction.........................................................................................….… 1
1.1 ZnSe and ZnSxSe1-x................................................................................. 1
1.2 Silicon Substrate..................................................................................... 2
1.3 Atomic Layer Epitaxy............................................................................ 2
1.4 Summary of This Thesis........................................................................ 3

Chapter Two System Description and Measurement Apparatus………………….. 6
2.1 MOALE System Configuration.....................................................… 6
2.1.1 Gas Handling system.……………………………………..… 6
2.1.2 Reactor and Heating System..……………………………….. 7
2.1.3 Exhaust System.………………………………………….….. 7
2.1.4 Protective System….……………………………………..…. 7
2.2 Measurement Apparatus.…………………………………………... 8
2.2.1 Composition Analysis..……………………………………… 8
2.2.2 Optical Measurement..………………………………….…… 8
2.2.3 Electrical Measurement….………………………….………. 8

Chapter Three The Study of High Quality ZnSe on Si by Atomic Layer Epitaxy
3.1 Introduction……………………………………………………….. 12
3.2 Experimental Procedure…………………………………………... 13
3.3 Growth Rate Analysis and Discussion……………………………. 14
3.3.1 Substrate Temperature……………………………………… 14
3.3.2 The Mole Flow Rate of DMZn……………………………... 15
3.3.3 The Mole Flow Rate of H2Se……………………………….. 16
3.3.4 The Pulse Duration of Purge H2………………………………. 17
3.3.5 Pressure of Chamber during the Growth.…………………… 17
3.3.6 Digital Growth in Nature…………………………………… 17
3.4 Composition Analysis and Discussion…………………………… 17
3.4.1 SIMS of ZnSe Thin Film…………………………………… 18
3.4.2 X-ray Diffraction Measurements of ZnSe Thin Film………. 18
3.5 Photoluminescence Measurements and Discussion………………. 18
3.6 Electrical Measurements and Discussion………………………… 19
3.6.1 Electrical Properties of ZnSe Schottky Diodes…………….. 19
3.6.2 Effect of Annealing Temperature on Electrical Properties
of the Metals-ZnSe Schottky Contacts.………………….... 20
3.7 Conclusions………………………………………………………. 20

Chapter Four Atomic Layer Epitaxy Growth of ZnSxSe1-x Epitaxial Layers Lattice-Matched to Si Substrates
4.1 Introduction………………………………………………………. 42
4.2 Experimental Procedure………………………………………….. 43
4.3 Growth Rate analysis and Discussion……………………………. 43
4.3.1 The Pulse Duration of H2Se………………………………... 44
4.3.2 The Mole Flow Rate of H2Se………………………………. 44
4.3.3 The Mole Flow Rate of H2S………………………………... 44
4.3.4 Substrate Temperature……………………………………… 44
4.4 Composition Analysis and Discussion…………………………… 45
4.4.1 X-ray Diffraction Measurements of ZnSxSe1-x Thin Film….. 45
4.4.2 SEM Micrographs of ZnSxSe1-x Thin Film…………………. 45
4.4.3 SIMS of ZnSxSe1-x Thin Film………………………………. 46
4.4.4 SEMEDS of ZnSxSe1-x Thin Film…………………………... 46
4.5 Photoluminescence Measurements and Discussion………………. 46
4.6 Electrical Measurement and Discussion………………………….. 47
4.6.1 Electrical Properties of ZnSxSe1-x Schottky Diodes….…..… 47
4.6.2 Hall Mobility……………………………………………….. 47
4.7 Conclusions………………………………………………………. 47

Chapter Five ZnSe/ZnS Strained Quantum Well Structures on Si Substrates by Atomic Layer Epitaxy
5.1 Introduction.………..…….………….…………………………… 66
5.2 Experimental Procedure………………………………………….. 67
5.3 Composition Analysis and Discussion…………………………… 68
5.3.1 SIMS of ZnSe/ZnS Strained Multiple Quantum Well
Structures.…..……………………………………………… 68
5.3.2 X-ray Diffraction Measurements of ZnSe/ZnS Strained
Multiple Quantum Well Structures.…..…………………… 69
5.3.3 TEM Microphotograph of ZnSe/ZnS SMQW...…………... 69
5.4 Photoluminescence Measurement and Discussion……………….. 69
5.4.1 PL of ZnS(1000Å)/(ZnS)n/ZnSe(1000Å) Strained Single
Quantum Well Structures.………………………………… 69
5.4.2 PL of ZnSe/ZnS Strained Multiple Quantum Well Structures. 70
5.5 Electrical Measurements and Discussion..………………………. 71
5.5.1 Electrical Properties of ZnSe/ZnS Strained Multiple
Quantum Well’s Schottky Diodes………………………… 71
5.6 Conclusions..……………………….……………………… 72

Chapter Six Conclusion………………………………………………………………. 85

Reference………………………………………………………………………….. 88
Publication list...…………………………………………………………………... 91

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