本論文主題是以雙束聚焦式離子束顯微切割儀(dual-beam focused ion beam system , DB-FIB)作為工具，對使用有機金屬化學氣相沉積法成長於c-plane藍寶石基板之氮化鎵系列LED元件進行蝕刻，製作出次微米尺度的LED，並研究其光電特性。
由於藍光LED量子井結構為InGaN/GaN之異質接面，因晶格不匹配，將導致內建壓電場的產生，壓電場會造成能帶傾斜，進而降低電子、電洞波函數的重疊機率，使得發光效率減弱，此現象即為量子侷限史塔克效應(Quantum Confine Stark Effect, QCSE)。為了降低應力所產生的壓電場，將LED尺寸微小化，可達成應力釋放的目的，進而有機會增加LED內部量子效率。
實驗發現FIB應用於GaN材料蝕刻，可達到次微米等級之線寬，目前做出最小線寬達到約800nm，並且仍具有LED特性。再研究經由FIB 蝕刻過後的LED 發現，其相較未經蝕刻的元件出現明顯較大的漏電流，量測變溫電流-電壓特性(77-300K)發現此漏電機制在低溫下被抑制，代表此現象很有可能是由於缺陷能階輔助造成的復合現象。另一方面，由於蝕刻過後的元件，表面積與體積的比值變大，亦即單位體積下有較大的表面積，使得表面復合的現象也更為顯著，也使得漏電流增加。
在發光特性方面，在低階電流注入時，可以發現蝕刻過後的LED出現發光波長藍移的現象，此現象間接證明經由LED微小化的蝕刻能達到應力釋放的效果，另外由於應力釋放降低了QCSE效應，使得發光波長較不隨著電壓變化而有所移動，我們亦認為在達到次微米等級之元件，內部量子效率亦有所提升。至於半高寬的部分，經FIB蝕刻過後的元件相較於未蝕刻元件，在相同電流密度下有著較窄的半高寬，此原因可歸因於蝕刻過後元件漏電流較大，即其電阻率亦較小，因此產生的熱效應較小所導致。
此外，在發光頻譜中黃光的部分，我們發現蝕刻過後的元件出現兩個黃光峰值的訊號，而標準元件則沒有。這黃光訊號一般認為是由於氮化鎵材料缺陷所造成的雜質能階。根據SRIM(stopping range of ions in matter) 2008電腦模擬軟體模擬結果，FIB使用的鎵離子轟擊會對氮化鎵材料產生氮空缺(Nitride vacancy)以及鎵空缺(Gallium vacancy)，而這缺陷在氮化鎵中形成一缺陷能階，本文亦探討氮空缺及鎵空缺在氮化鎵中扮演的角色及缺陷能階位置。

In this essay, dual-beam focused ion beam system (DB-FIB) was used to finish dry etching process on the GaN-based LED devices which were growth on c-plane sapphire substrate by metal-organic chemical vapor deposition (MOCVD). By using this technique, we have fabricated the sub-micrum meter scale LEDs, and measured their electric property and light emission characteristics.
Due to the multi quantum wells (MQWs) of blue LED is formed by InGaN/GaN heterojuction, the lattice mismatch between GaN and InGaN generates naturally built-in piezoelectric polarization and leads to band tilt. The band tilt can abate the overlap of electron and hole wavefunction, and it results in the decreasing of luminescent efficiency. To lower the stress induced piezoelectric polarization, decreasing LED size will be a possible opportunity to release the crystal strain and increase the internal quantum efficiency.
In our experiment, we have already fabricated sub-micro meter scale GaN-based LED by DB-FIB. The scale of fabricated linewidth minimizes to 500nm and still maintains its LED property. It is obvious that after FIB etching the leakage current increases. According to the temperature-dependent (from 77K to 300K) of current-voltage characteristics, the quench of leakage current in low temperature might stem from the defect assist recombination (or call Shockley-Read-Hall recombination). On the other hand, LED specimen which were after process of FIB etching have larger surface-to-volume ratio, meaning that the surface recombination current is more significant.
When mention to optical properties, we can find that the peak wavelength of FIB-damage specimen show blueshift while LED device operate in low current density. This is the evident of stain release by scale down. Besides, strain release can reduce quantum confine stark effect made the luminescent wavelength almost not blueshift with the current increases, and it also promote the internal quantum efficiency. The full width of half maximum (FWHM) in the electric luminescent spectrum, FWHM of the LED device after FIB etching decreases with increasing current density. FIB damage could increase the leakage current and decrease the resistance, so that can decrease the heat generation, too.
There are two distinct yellow luminescent (YL) peaks in our LED devices after ion beam etching, which are not shown in the reference (un-etched) samples. A lot of papers have already studies this phenomenon, the YL is generally caused by GaN material defect. By using SRIM (stopping range of ions matter) 2008 simulate Ga ions incident into GaN, the result reveals there are a lot of vacancies generated (330 vacancy per 1000 Ga ion incident), especially Ga vacancies. We also make a study of Ga vacancy in GaN and draft the position of defect state in GaN band diagram.

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