InAs/GaAs自聚式量子點掺入銻與氮之特性研究

Abstract

本篇論文分為兩部分，分別探討於InAs量子點中摻入銻(Sb)的PL光性及AFM分析與摻入氮(N)的電性分析。 藉由PL與AFM研究於InAs量子點磊晶過程中加入銻元素，改變不同量子點磊晶厚度，探討其中銻原子對量子結構所造成的影響。由磊晶結果得知加入Sb產生表面活化效應(surfactant effect)，使磊晶模式Stranski-Krastanow(S-K) mode之2D轉3D的厚度增加，量子點形成厚度由1.68ML延緩至2.0ML。從PL與AFM量測結果發現，加入銻會產生相分離(phase seperation)，產生InAs-rich與InSb-rich的兩群量子點。隨著磊晶厚度增加，InSb-rich的量子點密度，逐漸追上InAs-rich的量子點。2.0ML與2.2ML之InAs-rich量子點低溫有很大的半高寬，代表這些小尺寸量子點不均勻，溫度上升，明顯的紅移現象與半高寬的減少，表示穿隧效應載子容易從高能階往低能階移動。隨著磊晶厚度增加，量子點彼此間隔愈小，點與點之間傳遞所需熱動能愈小，導致從InAs-rich量子點傳遞至InSb-rich量子點的現象於較低溫就能看見。 利用導納頻譜(C-f G/f-f)量測、深層能階暫態頻譜(DLTS)、電容暫態頻譜(Capacitance transients)等電性量測方式探討在InAs/InGaAs dots-in-well的結構中的量子點加入氮，研究其中氮原子對量子點所造成的影響。無摻氮樣品溫度18K時載子時間常數仍小於1E-6秒，沒有缺陷。有摻氮樣品於溫度300K載子時間常數約1E-3 ~1E-5秒，有缺陷能階產生，造成載子空乏。以深層能階暫態頻譜量測，此缺陷能階位於傳導帶下方約0.2~0.23eV，缺陷濃度約1.1E15cm-3，求得捕捉位能障高度0.15eV。要造成空乏區寬度0.25μm與位能障高度0.15eV，所需要的的缺陷濃度為1.06E15cm-3。推測直接將氮摻入量子點會產生缺陷造成載子空乏，此缺陷能階位於導帶下方約0.2~0.25eV，缺陷濃度為1~2.8E15cm-3，產生位能障0.15eV，空乏寬度0.25μm。

This thesis is divided into two topics, including optical properties of InAsSb/GaAs quantum dots and electric properties of InAsN/InGaAs Dots-in-well structure. The effect of Sb incorporaton into self-assembled InAs/GaAs quantum dots(QDs) is investigated by photoluminescence(PL) and atomic force microscope(AFM). Three samples with different QDs deposition of 2.0, 2.2 and 2.8ML, are grown by molecular beam epitaxy(MBE). Sb reacts in InAs/GaAs system as a surfactant, which increases the critical thickness from 1.68ML to 2.0ML at which the growth mode changes from two-dimentional(2D) to three-dimentional(3D) growth. The results of PL and AFM data show that QDs are divided into two groups, InAs-rich and InSb-rich. This fully demonstrates the phase separation of InAsSb QDs. With thickness of epi-layer increasing, density of InSb-rich QDs is higher. For small deposition of 2.0ML and 2.2ML, a large FWHM at 25K is observed, implying a poor uniformity of these QDs size. With temperature increasing, trasfer of electrons from InAs-rich QDs to InSb-rich QDs is easier. With spacing of QDs decreasing, the lower temperature is needed for electrons transfer. The effect of N incorporation into the InAs/InGaAs QDs is investigated by admittance spectroscopy, capacitance transients and deep-level transient spectroscopy. No traps are observed in the QDs sample without N incorporation. The emission time of electrons from QDs is less than 1E-6 sec at 18K. However, the QDs sample with the N(17%) incorporation directly into the QDs would introduce defect traps which cause the carrier depletion. The emission time for electrons from defect traps is about1E-3~1E-5 sec at 300K. The capture barriers Eσ=0.15eV, traps level Et=0.2~0.25eV and traps concentration Nt=1~2.8E15cm-3 are measured by DLTS. In comparison, in order to make depletion width W=0.25μm by C-V measurement and barriers Eσ=0.15eV, the traps concentration Nt=1.06E15cm-3 is needed.