掺雜不同氮含量的InAs/InGaAs量子點與不同長晶速率的InGaAsN單一量子井之電性研究

Abstract

中文摘要 本篇論文主要是藉由電流-電壓(I-V)、電壓-電容(C-V)、導納頻譜(C-F)、深層能階暫態頻譜(DLTS)等電性量測的方式探討在波長1.3μm的InAs/InGaAs dots in well的結構中分別在量子點與量子井加入氮，研究其中氮原子對量子結構所造成的影響。從C-V量測結果中發現完全沒有加入氮的樣品有兩個量子峰值(quantum peak)，發現它們很有可能是分別是來自量子井與量子點的載子所形成，利用它們peak 出現的位置所對應的偏壓，可以得到量子點的放射能階比量子井深0.2eV。而將氮(0.4~1%)加在InGaAs well的兩片樣品都只觀察到量子井峰值。在這三片樣品中所出現的quantum peak對頻率都沒有響應，這表示載子從量子井和量子點放射出來的時間非常短，在溫度18K時小於10-6s。由於這三片樣品的品質都還很好所以從導納頻譜與DLTS都沒有發現缺陷訊號。然而，對於將氮(17%)直接加在InA量子點的樣品，我們從C-V量測結果中發現當高溫低頻時，在InAsN/InGaAs層有載子堆積的峰值形成；而低溫高頻時則形成一段載子空乏區。由C-F量測結果，我們可以得到電子從InAsN/InGaAs層放射出來的時間常數約10-4s(T=300K)且活化能為0.42eV(2.32*10-14cm2)。由於其PL訊號非常的差，因此我們相信將氮直接加在量子點會在量子結構層產生缺陷陷阱(at 0.42eV)造成載子空乏。 接著我們繼續研究不同的長晶速率所成長的InGaAsN單一量子井結構的特性。PL的結果顯示長晶速率快的樣品，其量子井放射波長在1.3µm而長晶速率慢的樣品的訊號卻是非常寬。由C-V量測結果可以觀察到長晶速率快的樣品有不隨頻率變化的量子井峰值形成，而長晶速率慢的樣品則發現有兩個不同缺陷造成有兩個偏壓下的電容值會隨頻率調變:一個出現在低溫時(T~80K)，偏壓-2V附近也就是InGaAsN層，另一個則是出現在高溫時(T~300K)偏壓-4V附近。我們相信這兩個缺陷都發生在InGaAsN層，偏壓在-4V表示其缺陷能階在較深的位置。藉由C-F與DLTS，我們可以得到它們的活化能分別為12meV~83meV與0.21eV。這兩個缺陷會在InGaAsN層空乏自由載子，這可能就是導致它PL訊號很差的原因。對照TEM圖可以看到長晶速率快的樣品有很平坦的quantum well 接面，而長晶速率慢的樣品在InGaAsN層變成三維成長，可能是由於氮原子聚集或分離的關係。因此我們推論電性量測上所發現的那些缺陷都與氮不均勻分佈有關。

Abstract The effect of N incorporation into the 1.3μm InAs/InGaAs quantum dots(QDs) is investigated by current-voltage(I-V),capacitance-voltage(C-V),admittance and deep-level transient spectroscopy﹒For the QD sample without any incorporation, C-V profile shows two quantum peaks which are probably originated from quantum well(QW) and QD, respectively﹒From their peak separation in voltage, the QD level is estimated at energy position of 0.2eV below the QW level﹒For the QD sample with the N(0.4~1%) incorporation into the InGaAs well, only single quantum peak is observed﹒All the quantum peaks in these samples are found to be frequency-independent, indicating that the emission time from QW and QD must be less than 10-6s at 18K﹒Quality of these quantum structures is good since no traps are observed either by admittance spectroscopy or DLTS﹒However, for the QD sample with the N(17%) incorporation directly into the QD,C-V spectra show significant dispersion over frequency with carrier depletion at low temperatures and carrier accumulation at high temperatures around the QW/QD region﹒From C-F spectra, we determine the emission time for electrons from around QW/QD to be ~10-4s(at 300K),with activation energy of 0.42eV(2.32*10-14cm2)﹒combining with the poor PL spectra, we believe that N incorporation directly into the QD would introduce around the QW/QD region defect traps(at 0.42ev) which cause the carrier depletion﹒ We continue this investigation by studying the effect of growth rate on the properties of InGaAsN single QW structures which emit at 1.3μm﹒The PL results show a quantum emission at 1.3μm for the high-growth-rate sample and very broad spectra for the low-growth-rate sample﹒While the high-growth-rate sample shows frequency-independent quantum peak, the low-growth-rate sample shows two frequency-dependent capacitance dispersions due to two different traps: one appears at low temperatures(~80K) around -2V where the QW locates and the other appears at high temperatures(~300K) around -4V﹒We believe that these two trap locate at same region around the QW and the bigger bias (-4V) just indicates a deeper energy position﹒From admittance and DLTS, we determine their activation energies to be 12~83meV and 0.21eV﹒These two traps deplete the free electrons around the QW region and are probably responsible for the poor PL spectra observed﹒In contrast to a flat QW interfaces in the high-growth-rate sample, TEM data show a 3-D growth of the InGaAsN layer probably due to N clusterization in the low-growth-rate sample﹒Therefore, we conclude that these defect taps are probably related to the nonuniform N distribution﹒