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研究生:周維揚
研究生(外文):Chou, Wei-Yang
論文名稱:調制光譜研究InAlAs,InP的表面費米能階與表面態分佈
論文名稱(外文):Modulatiion Spectroscopy Studies of the Surface Fermi Level and Surface State Distribution of InAlAs and InP
指導教授:黃正雄黃正雄引用關係
指導教授(外文):Hwang Jenn-Shyong
學位類別:博士
校院名稱:國立成功大學
系所名稱:物理學系
學門:自然科學學門
學類:物理學類
論文種類:學術論文
論文出版年:1997
畢業學年度:86
語文別:中文
論文頁數:132
中文關鍵詞:調制光譜表面費米能階表面態分佈
外文關鍵詞:InAlAsInPInAlAsInPModulation SpectroscopySurface Fermi LevelSurface State Distribution
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在本論文中,我們首先利用光調制光譜(PR)及電調制光譜(ER)技術
研究一系列InP表 面-本質-n+(surface-intrinsic-n+,SIN+)結構的表
面費米能階及介面性質,由樣品的 PR譜線之Franz-Keldysh
Oscillations (FKOs)求其內建電場和表面費米能階。我們發現 矽摻雜
之緩衝層和基底的摻雜濃度相同時,其內建電場隨未摻雜之頂層厚度減少
而增大。 而基底為Fe摻雜的半絕緣(SI)InP時,由其PR光譜所求得的電
場則與頂層厚度無關。我們 應用ER技術只調制頂層的電場並由其ER譜線
得到頂層的內建電場,我們發現這兩類樣品的 內建電場皆隨頂層厚度遞
減而漸增,而表面費米能階則維持一定值。從這些結果我們證明 了InP
的表面費米能階乃釘札在能隙間且距導帶邊緣0.35 eV處。 接著我
們探討了一系列In1-xAlxAs SIN+結構的能隙及表面費米能階隨組成x、未
摻雜 之頂層厚度和溫度的變化,並計算其表面態的密度。我們發現Al的
莫耳分率在0.42到0.57 的範圍中,表面費米能階的位置並不是釘札在半
能隙上,而是在距離導帶邊緣0.5 eV到 0.81 eV間變化。此結果與相同
結構的Al1-xGaxAs不同,Al1-xGaxAs的SIN+結構的表面費 米能階已被證
實是釘札在半能隙的位置。繼之,我們利用蝕刻溶液改變頂層厚度再量測
其 PR光譜,我們發現表面費米能階隨未摻雜之頂層厚度的改變而變化,
對每一種Al莫耳分率 的樣品均存在一特定厚度範圍(characteristic
regions),在此範圍中表面費能階是些微 釘札(weakly pinned),此外
,縱使利用不同比例的蝕刻溶液,我們亦發現內建電場與蝕刻 過程無關
。從內建電場和表面費米能階與未摻雜層厚度的相關性,我們提出了雙表
面態模 型來解釋研究結果,假設在能隙中有二個分立的表面態分佈,根
據此雙表面態分佈模型我 們計算出靠近導帶的表面態密度最小者
為1.02*10^11 cm^(-2),另一個靠近價帶者最小 為2.91*10^11 cm^(-2)
。 最後,我們研究In(0.53)Al(0.47)As的表面蕭特基勢壘對溫度的
響應,以PR光譜量測不同溫度下之蕭特基勢壘,由實驗結果來印證雙表面
態模型的正確性。我們以雙表面態模 型為基礎,根據擴散理論、熱游子
發射理論、鏡像力的效應與電流/電壓之關係,提出理 論分析得到蕭特
基勢壘與溫度、表面費米能階釘札位置、表面態密度等的關係。由實驗值
與理論關係式的擬合結果我們得到表面費米能階的兩個釘札位置,分別距
離導帶邊緣0.47 eV 和1.00 eV,其所對應之表面態密度分別為2.61*10
^11和2.73*10^11 ,理論擬合之結果與改變未摻雜層厚度所得的結果十
分吻合,再次證明了雙表面態模型的正確性。此外, 我們亦得到與表面
態有關的參數如:幾何因子r1=4.50*10^(-4)、r2=4.70*10^(-4),理想
因子h1=3.60、h2=2.90等等。
The techniques of the photoreflectance (PR) and
electroreflectance (ER) were used to study the built-in
electric fields and the surface Fermi levels of InP surface-
intrinsic-n+(SIN+) structures. The substrates of SIN+ structures
are either Fe-doped semi-insulated InP or Sn-doped N+ InP with
same doping concentrations as its buffer layer. The built-in
electric field and the Fermi level were calculated from the
Franz-Keldysh oscillations (FKOs) of the photoreflectance
spectra. Our studies found that for the samples with the same
doping concentration in buffer layer and substrate, the built-in
electric field increases as their top layer thickness
decreases. The surface Fermi level, on the other hand, remains
approximately constant. For samples with a semi-insulated
substrate, the photoreflectance spectra indicate the
simultaneous existence of two built-in electric fields, one in
the top layer and the other at the interface region between the
buffer layer and substrate. ER spectra were measured with the
application of a modulation electric field across the top layer.
The built- in electric field across the top layer obtained from
the ER spectra increases as the top layer thickness decreases
while the surface Fermi level, again, remains approximately
constant. Next, we have studied the band gaps and the
surface Fermi level positions of a series of In1-xAlxAs SIN+
structures at room temperature by PR. Experiments demonstrated
that over the aluminum mole concentrations x from 0.42 to 0.57,
the surface Fermi level is not pinned at midgap, as commonly
believed, but instead varies, respectively, form 0.50 to 0.81
eV below the conduction band edge. The samples were grown by
molecular beam epitaxy with a undoped layer thickness of 1000
A. The undoped layer was subsequently etched to 800, 600, 400,
and 200 A. Different chemical solutions were used in the
etching process and the built-in electric field is found
independent of the etching process. While the surface Fermi
level, in general, varies with the undoped layer thickness,
there exists, for each Al concentration, a certain range of
thickness within which the surface Fermi level is weakly
pinned. From the dependence of electric field and surface Fermi
level on the undoped layer thickness, we conclude that the
surface states distribute over two separate regions within the
energy band gap and the densities of surface states are as low
as 1.02*10^11 cm^(-2) for the distribution near the conduction
band and 2.91*10^11 cm^(-2) for the distribution near valence
band. Finally, we measured the surface Schottky barrier of
In(0.53)Al(0.47)As SIN+ structure as a function of temperature.
Based on diffusion theory, thermionic- emission theory, and
the relation between the image force effect and current/
voltage, a theoretical relation of the surface Schottky barrier
and temperature, pinning positions of the surface Fermi level,
surface state densities etc. was obtained. From the least
squares fits of the experiments data to the theoretical
relation, we obtained the pinning positions, 0.47 eV and 1.00 eV
from the conduction band edge which correspond to the
densities of surface state, 2.61*10^11 and 2.96*10^11 cm^(-2),
respectively. The results are in good agreement with those
obtained from the study by changing the thickness of the undoped
layer. This study has further approved the model of double
distributions of the surface states. Furthermore, the surface
state dependent parameters, the geometric factors (r1=4.50*10
^(-4) and r2=4.70*10^(-4)) and the ideal factors (h1=3.60 and
h2=2.90) were also obtained from the fitting results.
封面
目錄
第一章 緒論
第二章 光調制光譜學的理論
2-1 調制光譜與介電函數
2-1-1 躍遷機率
2-1-2 光學常數
2-2 光調制光譜
2-2-1 低電場調制
2-2-2 Franz-Keldysh 振盪
2-3 光調制光譜的機制
2-4 譜線的擬合
第三章 實驗裝置
3-1 光調制光譜的實驗裝置
3-2 電調制光譜的實驗裝置
第四章 InP 的表面及介面性質研究
4-1 樣品的條件
4-2 光調制光譜學之量測
4-3 電調制光譜學之量測
4-4 結論
第五章 InA1As 的表面費米能階研究
5-1 樣品的條件
5-2 表面費米能階與組成之關係
5-3 表面費米能階和表面態的分佈
5.3.1 樣品之條件與量測
5.3.2 表面態分佈模型
5-4 表面態密度之計算
5-5 結論
第六章 溫度對費米能階的影響
6-1 樣品的準備與量測
6-2 理論分析
6-3 能隙之溫度參數
6-4 結論
第七章 總結
附錄
參考文獻
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