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標題: | 掃描探針顯微術在半導體及壓電材料上奈米尺度的光電現象研究 NANOSCALE ELECTRIC AND OPTICAL PHENOMENA IN SEMICONDUCTORS AND PIEZOELECTRIC MATERIALS INVESTIGATED BY SCANNING PROBE MICROSCOPY |
作者: | Wei-Sheng Su 蘇偉盛 |
指導教授: | 陳永芳(Yang-Fang Chen) |
關鍵字: | 原子力顯微術,電力顯微術,氮化銦,氮化鎵,壓電效應,PMN-37PT,壓電力顯微術, AFM,EFM,InN,GaN,Piezoelectric effect,PMN-37PT,PFM, |
出版年 : | 2007 |
學位: | 博士 |
摘要: | 摘要
在這本論文中,我們使用掃描探針顯微術去研究許多半導體和壓電材料上的新發展。在這裡發現許多有趣的現象,而新的物理機制也被提出。下面是本文的一些重要結果: 1. 在這裏我們介紹及建立一個新的技術。這技術是在電子力顯微鏡上加一個光源改變表面局部的電性改變,目的就是利用電子力顯微鏡去觀察照光後材料局部的電性的變化。在這裏我們是討論氮化銦磊晶層的局部電性變化。結合原子力顯微術,我們可以發現到表面態位密度在表面的凹處較凸處為大,以及在表面有一層電子層。另外在這裏我們也發現表面態造成的巨大能帶可以與之前的文獻上吻合。在這裏我們也指出光機發電子力光譜技術是觀察局部電子躍遷一個非常強大的工具。 2. 在這裏我們成功的在氮化鎵奈米柱上將力學能轉化成電能。這個實驗是利用導電性原子力顯微術去彎曲氮化鎵奈米柱。機制是結合了壓電及半導體的特性去產生電場及電流。這個結果提供了一個新方法去將周圍環境的力學能轉化成電能,這方法可以利用去做成自我發電的奈米元件。 3. 我們結合氮化鎵本身的內建表面電場、壓電特性、電子電洞對、及外加入射發現了許多新的現象。當入射光強度增加時,我們可以觀察到光激發螢光的峰值紅移,及拉曼聲頻支的聲子頻率紅移。這個機制認為是表面電場被光機發的電子電洞對屏蔽,經由逆壓電效應,內建的應力被降低。這個內建電場的存在可以用表面電位顯微術的觀察得到證明。這些新的現象是由於奈米材料上表面占了很重的比例造成的。這些現象會是製作奈米元件的原理。 4. 最近,(Pb(Mg1/3Nb2/3)O3)0.63(PbTiO3)0.37 (PMN-37PT)被發現當他製作成一個沒有基座的結構時,他的壓電反應在電場約2kV/cm時會增加。這裏我們藉由壓電力顯微術提供了一個直接證據,這證據直接觀察到四十微米的樣品在這個電場下極化方向的轉變。實驗結果顯示他的極化方向傾向於平行樣品表面的方向。而這些平行表面的極化在1.3 kV/cm和1.9 kV/cm之間可以完全轉向。另外將這塊樣品做成懸臂形狀時的量測顯示在1.3 kV/cm和2 kV/cm有增強的現象,且最大的壓電反應為2700 pm/V。這結果跟壓電力顯微術的結果可作一個連結。而極化完全轉巷的店賞遠小於一般的薄膜結構。 In this thesis, we have applied the powerful technique called scanning probe microscopy to investigate several newly developed semiconductors as well as piezoelectric materials. A variety of interesting phenomena have been discovered and the related physical mechanisms have also been proposed. The main features of our results are as follow: (1) Electrostatic force Spectroscopy: Application to local electronic transitions in InN epifilms. A technique based on electrostatic force microscopy in which light is used to change the charge states of the local region in a solid is introduced and demonstrated. This technique provides a unique feature that it can be used to probe local electronic transitions of a solid in a sub-micron scale. As an illustration, it has been applied to study local electronic structure in InN epifilms. Combining with atomic force microscopy, it is found that surface state density in the dale region is larger than that of the pinnacle region, and an electron accumulation layer does exist on the surface. In addition, the magnitude of the surface band bending obtained for the regions with different surface states is consistent with the result measured by other techniques. We point out that light-induced scanning electrostatic force spectroscopy is a very useful tool to probe the local electronic transitions of a solid in a sub-micron scale with high sensitivity. (2) Generation of electricity in GaN nanorods induced by piezoelectric effect. Conversion of mechanical energy into electric energy has been demonstrated in GaN nanorods. The measurement was achieved by deflecting GaN nanorods with a conductive atomic force microscope PtIr tip in contact. The mechanism relies on the coupling between piezoelectric and semiconducting properties in GaN nanorod, which creates a strain field and drives the charge flow across the nanorod. The result shown here opens up a new opportunity for harvesting electricity from wasted mechanical energies in the ambient environment, which may lead to the realization of self-powered nanodevices. (3) Built-in surface electric field, piezoelectricity and photoelastic effect in GaN nanorods for nano-photonic device. Novel behaviors arise from the coupling between built-in surface electric field, piezoelectricity, electron-hole pairs, and external light beam have been observed in GaN nanorods. When optical excitation density was increased, a blueshift in the photoluminescence spectra and a redshift in the frequency of GaN A1(LO) phonon were observed. The underlying mechanism was attributed to the screening of built-in surface electric field by photoexcited carriers, and through the converse piezoelectric effect, the internal strain was reduced. The existence of built-in surface electric field in GaN nanorods has been confirmed by scanning Kelvin probe microscopy. Our results firmly establish that the photoelastic effect does exist in GaN nanorods. This finding reveals novel properties arising from the inherent large surface-to-volume ratio of nanostructures, it thus is applicable to many other nanomaterials. It also underpinns the principle for applications in nano-photonic devices. (4) Piezoelectric Enhancement and Domain Switching in PMN-PT Polycrystalline Sheets by Piezoresponse Force Microscopy. Recently it was found that the piezoelectric response of substrate-free polycrystalline (Pb(Mg1/3Nb2/3)O3)0.63(PbTiO3)0.37 (PMN-37PT) sheets increased by several fold at applied electric fields E ≧ 2 kV/cm. Here we provide direct evidence of polarization switching occurring at such electric fields through piezoresponse force microscopy on a 40 |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/30181 |
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