分子束磊晶成長InAs/InGaAs量子點之銻表面活化效應

Abstract

本論文主要是探討InAs/InGaAs自聚式量子點之銻(Sb)表面活化效應，藉由光激發螢光(PL)、原子力顯微鏡(AFM)、穿透式電子顯微鏡(TEM)以及電流-電壓(I-V)、電容-電壓(C-V)電性量測方式探討掺入不同含量的Sb對InAs量子點的影響。我們成長三片不同Sb含量的InAsSb量子點，Sb分子束的等效壓力(Beam Equivalent Pressure,BEP)分別為0(torr)、1.8×10-8(torr)、6×10-8(torr)，由PL量測得知隨著Sb含量的增加，發光波長從1323nm藍移至1295nm，顯示量子點變小顆或應力變大的效應，這個現象亦導致了Sb量最多的樣品基態和第一激發態離砷化鎵導帶較近，使得溫度升高載子侷限力較差。變功率PL得知隨著Sb量增加，在室溫(300K)時第一激發態/基態(E./G.)強度的比值從1.06提升至7.057，在低溫(25K)這個現象更明顯，第一激發態訊號大到涵蓋基態訊號，顯示Sb含量多的樣品基態容易被填滿進而填第一激發態，所以隨Sb含量增加量子點密度有明顯下降的趨勢(二個數量級)。為了進一步證實這個推論，我們從AFM影像來估計量子點密度，隨著Sb含量增加量子點密度由3.5×109cm-2下降至6×108 cm-2到小於1×108 cm-2(Sb含量最多的樣品)。 在低溫低頻之電容-電壓電性量測發現，隨著Sb量增加縱深分佈的(E./G.)比值從0.6937提升至1.2102與光性分析有相同趨勢，半高寬(FWHM)有下降趨勢顯示隨Sb增加量子點有較均勻的現象；在Sb含量最多的樣品發現，隨著量測頻率下降基態的濃度有明顯增加的趨勢(2×1017增加至2.15×1019)，使的基態峰值顯得更陡峭，由於可以在電性明顯的量測出基態的變化，是因為量子點密度低與均勻度好的原因，這個結果與之前的分析有相同趨勢。

由以上的結果顯示出Sb的掺入可以有效延長wetting layer的成長，增加2D轉3D長晶模式的臨界厚度，抑制量子點的形成，量子點密度減少二個數量級以上，並且使量子點長的更小顆更均勻，對降低量子點密度的應用提供了一個有效的方法，將有助於單一量子點基本性物理之探討。

Surfactant effect of Sb on self-assembled InAs/InGaAs quantum dots(QDs) is investigated by current-voltage(I-V) , capacitance-voltage(C-V) , photoluminescence(PL) , atomic force microscopy(AFM) and cross-section transmission electron microscopy(TEM). Three samples with different Sb beam equivalent pressure(BEP) of 0, 1.8×10-8and 6×10-8 torr are grown by molecular beam epitaxy(MBE). With increasing Sb beam flux, the room-temperature emission from the InAs QDs is blue shifted from 1323nm to 1295nm and the emission intensity is reduced. This indicates a reduction of dot size as Sb beam flux is increased. With increasing Sb beam flux, we find an increase of the ratio of the PL intensity of excited state/ground state from 1.06 to 7.057, suggesting an easy fill up of the ground state for the sample with high Sb content. This result shows that increasing Sb beam flux reduces the QDs density. This is consistent with atomic force microscope results that show a marked reduction in the dot density from 3.5×109 cm-2 to less than 1.0×108 cm-2. In addition. The C-V profiles display two well-separated sharp peaks that are originated from the ground and excited states of the QDs, respectively , suggesting an improved uniformity and decreased dot density.

The addition of Sb can retard the 3D growth mode and expand the critical thickness of the growth mode from 2D to 3D. The results here show a reduction two orders of magnitude in the dot density; a decreased dot size and improved uniformity. This technique is effective in reducing the dot density and is useful for the study of the properties of a single quantum dot.