重矽摻雜之砷化銦與有序排列磷化銦鎵之光學特性研究

Studies on the Optical Characteristics of Heavily Si-doped InAs and Ordered InGaP

洪廖啔靖(Chi-Jing Hong-Liao)

指導教授 ： 林浩雄

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.01172

摘要

本論文研究以分子束磊晶法成長的重矽摻雜砷化銦與以有機金屬化學氣相沉積法成長的有序排列磷化銦鎵之光學特性。第一部分探討重矽摻雜砷化銦的拉曼頻譜，實驗中除了發現LO聲子與電漿作用所形成的PLP耦合模態之外，還發現了由於屏蔽效應減弱所導致的LO模態。隨著濃度提升，PLP模態位置由LO模態逐漸往TO模態移動，此現象與介電方程式推導的模態趨勢相違背，我們將此現象歸因於由於晶格振盪導致內部感應電場產生，當電場的空間變化速度太大，使得載子無法有效屏蔽時，PLP模態回復接近接近LO模態位置；隨著濃度提升，感應電場逐漸被有效屏蔽，PLP模態位置將往TO模態移動。而屏蔽效應的強弱由模態的波向量與湯姆斯費米波向量值決定，經由計算比較，我們發現LO模態的出現是來自於表面累積層的散射，PLP模態則來自於非累積層的貢獻。當濃度高於5x10^19 cm^-3，我們發現LO模態不遵守拉曼選擇規則，此現象可能由於摻雜濃度較高時，費米能階高於表面能階，表面形成的空乏層誘發電場所導致。另外，我們從傅立葉轉換紅外線光譜儀所量測的反射頻譜推知電漿頻率的位置，並與拉曼量測所得到的PLP模態位置相近。
本論文的第二部分研究有序排列磷化銦鎵的拉曼散射與光激螢光譜。我們經由室溫的光激螢光譜與X-ray繞射頻譜以理論公式計算樣品的有序排列程度，並透過拉曼頻譜上相對應的模態強度推算其深谷數值(valley depth ratio)，發現隨著有序排列的程度增加，拉曼頻譜上InP-like與GaP-like LO模態之間的凹谷深度也將隨之上升，導致深谷數值下降，此現象與文獻上的趨勢相同。此外，當雷射光源沿著[1-10]極化方向入射時，我們可以從拉曼頻譜上觀察到來自(1-11)和(-111)晶格有序排列所形成C3V對稱結構的354和380 cm-1峰值，然而當極化方向旋轉九十度沿著[110]方向時，380cm-1的聲子模態依舊可以被觀察到，我們推測其來自於(111)和(-1-11)平面上的有序排列。

關鍵字

拉曼散射 ； 光激螢光譜 ； 矽摻雜之砷化銦 ； 磷化銦鎵 ； 有序排列 ； 屏蔽效應 ； 湯姆斯費米波向量

並列摘要

This thesis presents the optical characteristics of heavily Si-doped InAs, grown by gas-source molecular beam epitaxy, and InGaP, grown by metal-organic vapor phase epitaxy. In the first portion of this thesis, we report the Raman scattering of the heavily Si-doped InAs. The Raman spectra show coupled plasmon LO-phonon (PLP) mode and unscreened LO mode. The frequency of the PLP mode is slightly lower than that of the LO mode and gradually reduces to frequency of the TO mode when the carrier density increases, in conflict with the PLP mode equation. This abnormal behavior becomes less significant when we replaced the 514-nm laser by 632-nm laser. By comparing the LO wave-vector and the Thomas-Fermi screening wave-vector of each InAs bulk layer, we found that the screening effect is responsible for this abnormal behavior. The unscreened LO mode is attributed to the surface accumulation layer, whose thickness is too short to screen the LO mode. We also observed the forbidden unscreened LO mode for the samples with a carrier density higher than 5x10^19/cm^3, which is ascribed to the resonant enhanced scattering induced by space charge field of the surface layer. FTIR was used to measure the reflectance of the samples to obtain the plasma frequency. The result is in good agreement with the plasmon frequency determined from the Raman scattering.
In the second portion of this thesis, ordered InGaP material has been studied by Raman scattering and photoluminescence (PL) measurement. We used the energy gap determined from room temperature PL and the lattice mismatch determined from XRD to calculate the degree of order for each InGaP samples. Valley depth (b/a) ratio, determined from the unresolved GaP-like and InP-like LO modes, decreases with the increasing ordering degree and is close to the values reported in literature. Along [1-10] polarization, we observed two additional peaks at 354 cm-1 and 380 cm-1, which has been reported in literature and are relevant to the A(Z) mode of C3v symmetry resulting from the ordering arrangement on (1-11) or (-111) plane. The most striking is that the 380 cm-1 additional peak also appears when the measurement was taken along [110] polarization, indicating that the samples could contain ordering arrangement on (111) or (-1-11) plane.

並列關鍵字

Raman scattering ； Photoluminescence ； Si-doped InAs ； InGaP ； Ordering effect ； Screening effect ； Thomas-Fermi wave-vector

參考文獻

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