熱退火對掺入氮砷化銦量子點電子放射率之影響

Abstract

本篇論文樣品是以分子束磊晶(MBE)成長，藉由高解析穿透式電子顯微鏡(HRTEM)，光激發螢光(PL)，電流-電壓(IV)，電容-電壓(C-V)，導納頻譜以及深層能階暫態頻譜儀(DLTS)等量測方式探討在InAs量子點結構中掺入氮引致缺陷態，再經過熱退火處理後對量子結構的電子放射率之影響。總共有掺入氮原始樣品及四片不同溫度時間熱退火處理的樣品。先前實驗室的研究結果顯示，在沒有掺入氮的量子點結構中，載子從量子能階基態躍遷到第一激發態，然後再穿隧出去，求得0.058ev基態至第一激發態間的活化能。掺入氮的樣品中，在量子點區域產生了缺陷，我們並探討這缺陷對量子點能帶結構圖的電子放射率之影響。掺入氮樣品在量子點區域的電子放射由兩個機制所主宰，一個很強且寬活化能為0.38ev的訊號E1，及很弱活化能為0.15ev的訊號E2，分別對應到缺陷能階至GaAs導帶，量子點基態至GaAs導帶的能階差。我們發現熱退火可以削弱E1(缺陷)訊號，增強E2(量子)訊號，減少電子的放射時間及活化能階。從掺入氮樣品一直到熱退火800oc五分鐘樣品，我們看到ㄧ直連續不斷減少的量子躍遷能階活化能。此種現象可以以載子在量子能階的穿隧機制來解釋。掺入氮導致下層的GaAs區域載子空乏，並抑制了量子能階載子的穿隧機率。熱退火可以去除缺陷並恢復量子區的電子。增加熱退火溫度可以增強穿隧效應，導致愈來愈小的量子能階活化能，及愈來愈少的放射時間。因此，我們可以藉由在結構量子點裡製造一個缺陷態，再把這樣品拿去做熱退火處理，進而改變量子點穿隧機率來調變電子放射率。

The annealing effect of a nitrogen-induced state on the electron emission in InAs self-assembled quantum dots (QDs) has been investigated by high resolution transmission electron microscope (HRTEM), photoluminescence (PL), current-voltage (I-V), capacitance-voltage (C-V), admittance spectroscopy, and deep level transient spectroscopy (DLTS). As grown and four different annealing temperature and time samples are studied. Without N incorporation, electron emission from the QD to the GaAs conduction band occurs by tunneling through the first excited state with 0.058 eV, corresponding to the energy spacing between the QD electron ground and the first-excited states. With N incorporation, a deep defect trap in the QD is induced and we can investigate the effect of the electronic band structure of the QD on the electron emission with this trap. For as grown sample, the electron-emission properties in the QD region is governed by two emissions: a strong and broad emission E1 with 0.38 eV and a weak emission E2 with 0.15 eV, corresponding to the energy spacing between defect level and GaAs conduction band, the quantum dots ground state and GaAs conduction band edge, respectively. We find that annealing can weaken E1(defect) emission, enhance E2(quantum) emission, and significantly reduce the electron emission time and energy. A continuous reduction of electron-emission energy in quantum dots is observed from as grown to annealing 5 minutes at 800oC. This change of emission time and energy is explained by tunneling through the QD state. The N-induced traps in the GaAs bottom layer can induce additional carrier depletion and suppress tunneling emission rates. Annealing can remove the traps there and recovers the electrons in the QD. Increasing annealing temperature enhances the tunneling emission, leading to the continuous reduction of emission time and energy. Thus, by placing a defect state in the QD, annealing can be used to modify its electron-emission time by controlling the tunneling rate.