具非晶質矽合金調變週期類超晶格薄膜複層之低暗電流高熱穩定度平面矽基金屬–半導體–金屬光檢測器

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研究生：	魏燕伶 Yen-Lin Wei
論文名稱：	具非晶質矽合金調變週期類超晶格薄膜複層之低暗電流高熱穩定度平面矽基金屬–半導體–金屬光檢測器 Low Dark-Current and High-Thermal Stability Planar Si-Based MSM Photodetector with Thin Amorphous Silicon-Alloy Grade Superlattice-Like Multilayers
指導教授：	洪志旺 Jyh-Wong Hong
口試委員:
學位類別：	碩士 Master
系所名稱：	資訊電機學院 - 電機工程學系 Department of Electrical Engineering
畢業學年度：	92
語文別：	英文
論文頁數：	51
中文關鍵詞：	矽鍺、非晶質、光檢測器
外文關鍵詞：	SiGe, amorphous, MSM
相關次數：	點閱：14 下載：0
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論文提要
本論文主要探討非晶矽/非晶矽化鍺調變週期類超晶格薄膜複層在金屬-半導體-金屬光檢測器裡的應用。我們證實了利用非晶矽/非晶矽化鍺調變週期類超晶格薄膜的等效能隙梯度變化不僅能降低元件膝電壓，更因為能帶的不連續而能有效的改善以往的組成梯度能隙位障層所造成的許多缺點，進而有效的降低元件暗電流。此結構的元件在5 V偏壓、波長0.83 μm及10 μW雷射光入射時所得之光響應度、膝電壓與暗電流分別為0.1(A/W)、1.8 V與0.31 nA。再者，在一周期性波長0.83 μm、60 ps脈衝寬度的入射光及10 V偏壓下所得到的元件暫態響應平均半高寬(FWHM)和下降時間(fall-time)分別為116.1 ps 以及388.6 ps。與組成梯度能隙位障層與其它許多以高能隙非晶質薄膜層當作蕭特基能障輔助增高層所製成的元件比較，此結構擁有相當低的暗電流與膝電壓。為了研究元件在熱穩定度上的表現，我們也嘗試在不同的操作溫度下進行元件特性量測，而實驗結果顯示此元件擁有相當高的熱穩定度，在50 ℃時暗電流仍然低於2 nA以下。
我們也探討了非晶質調變週期類超晶格薄膜複層的厚度與組數對元件特性的影響。藉由選擇適合的複層厚度以及組數可以得到優化的元件特性。

Abstract
The alternated i-a-Si:H/i-a-SiGe:H grade superlattice-like layer (GSL) was firstly introduced in planar Si-based metal-semiconductor-metal photodetectors (MSM-PD’s) to smooth the abrupt band discontinuity between the c-Si and i-a-Si:H heterojunction. It was demonstrated that the i-a-Si:H/i-a-SiGe:H GSL structure could drastically improve the disorder-caused disadvantages of i-a-SiGe:H composition-graded layer (CGL), and effectively suppress the device dark-current, improve its temporal response without raising its knee-voltage like thick and high optical bandgap barrier layer in the application to MSM-PD’s. The responsivity, knee-voltage and dark-current for the device with i-a-Si:H/i-a-SiGe:H GSL were 0.1(A/W), 1.8 V and 0.31 nA, respectively, under a 5 V bias voltage and 0.83 μm 10 μW incident laser power. Also, the average full-width-at-half-maximum (FWHM) and transient fall-time of the device were 116.1 ps and 388.6 ps, respectively, under 10 V bias voltage and 60 ps 0.83 μm light pules. Very low dark-current, low knee-voltage device was obtained as compared with devices having i-a-SiGe:H CGL or other previously reported amorphous Schottky barrier enhancing layers. Device thermal-stability was also investigated, and the stability of the device with GSL was outstanding even at a high temperature of 50 ℃.
The influence of layer thickness and pair number of GSL on characteristics of a MSM-PD had been studied also. By choosing an appropriate thickness and pair number of GSL, the optimum performance of a MSM-PD could be obtained.

Contents
Abstract………………………………………………………………(Ⅲ)
Table Captions………………………………………………………(Ⅳ)
Figure Captions………………………………………………………(Ⅴ)
Chapter 1	Introduction………………………………………	1
Chapter 2	Device Operation Principles and Fabrication Processes………………………………………………	3
2-1  Operation Principles of MSM-PD’s……………	3
2-2  Responsivity ……………………………………	9
2-3  Response Speed…………………………………	10
2-4  Device Fabrication Processes……………………	13
Chapter 3	Measurement Techniques…………………………	18
3-1  Optical bandgap………………………………	18
3-2  Responsivity and response speed………………	18
Chapter 4	Experimental and Discussions………………………	23
4-1  Si-based MSM-PD’s with various kinds of
amorphous layers………………………………	23
4-2.   Thermal stability……………………………	27
4-3.  Optimization of the GSL layers………………	35
4-3-1. MSM PD’s with various pair numbers of   GSL……………………………………… 	35
4-3-2. MSM PD’s with various thicknesses of
GSL…………………………………	36
Chapter 5	Conclusion……………………………………………	45
References	…………………………………………………………	47
Table Captions
Table 2-1.	The deposition conditions of various amorphous films…	17
Table 2-2.	The deposition conditions of various metal films………	17
Table 4-1.	The thicknesses and pair numbers of i-a-Si:/i-a-SiGe:H multi-layers in various GSL’s for MSM-PD’s……………	37
Figure Captions
Fig. 2-1	(a) The schematic top-view of the MSM-PD with planar
interdigitated electrodes.
(b) The equivalent back-to-back diodes…………………	4
Fig. 2-2	(a) MSM structure, (b) charge distribution under low bias voltage, (c) electric-field distribution under low bias voltage, and (d) schematic energy-band diagram………	5
Fig. 2-3	Electric-field distribution and energy-band diagram of MSM under (a) reach-through condition, and (b) flat-band condition…………………………………………………6
Fig. 2-4	(a) Cross-section diagram of the MSM-PD with GSL.
(b) Schematic energy-band diagram of the GSL………	11
Fig.2-4	(c) The schematic energy-band diagram of the device under a bias voltage (Vbias) higher than flat-band voltage…	12
Fig.2-5	The PECVD system with a stainless steel mesh…	15
Fig.2-6	The fabrication process flow-chart of the MSM-PD with GSL layers………………………………………………	16
Fig. 3-1	The setup for measuring optical band-gap for amorphous film.………………………………………………………	20
Fig. 3-2	The setup for measuring responsivity of a MSM-PD……	21
Fig. 3-3	The setup for measuring transient response of a MSM-PD..	22
Fig.4-1	The schematic cross-section diagram of the device with GSL………………………………………………………	24
Fig.4-2	The schematic cross-section diagram of the device D2 with CGL, and D3 with only i-a-Si:H layer ……………………	25
Fig.4-3  	The comparison of photo-currents for MSM-PD’s with various amorphous layers………………………………	29
Fig.4-4	The comparison of dark-currents for MSM-PD’s with various amorphous layers………………………………	30
Fig.4-5	(a) The comparison of temporal responses for D1 and D2,
and (b) The 3dB bandwidths for D1 and D2………………	31
Fig.4-6	The photo-currents for D1 at several temperatures……… 	32
Fig.4-7	The photo-currents for D2 at several temperatures………	33
Fig.4-8	The dark-current comparison for D1 and D2 at several temperatures………………………………………………	34
Fig.4-9  	The comparison of photo-currents for devices with various pair numbers of GSL……………………………………	38
Fig.4-10  	The comparison of dark-currents for devices with various pair numbers of GSL…………………………………	39
Fig.4-11	(a)	The temporal responses, and (b) 3dB bandwidths for
devices with various pair numbers of GSL……………	40
Fig.4-12	The comparison of photo-currents for devices with various thicknesses of GSL………………………………………  	42
Fig.4-13	The comparison of dark-currents for devices with various
thicknesses of GSL………………………………………	43
Fig.4-14	(a) The temporal responses and (b) 3dB bandwidths for
devices with various thicknesses of GSL…………………	44

                                

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