應用一次性氫離子佈植製程於氮化鎵發光二極體元件之光電特性研究

Abstract

本論文為將氫離子佈植於N型氮化鎵以及P型氮化鎵上，並量測分析其歐姆接觸特性，預期可以在N型佈植區域有效降低N型接觸電阻，使整體串聯電阻下降，進而讓導通電壓降低；在P型佈植區域可以提升P型串聯電阻，使其有電流阻擋層的效果去改善電流擁擠現象，期望上述之N型和P型的氫離子佈植技術，可利用一次性同時佈植之製程應用於氮化鎵發光二極體元件上，探討其光電特性。 在本論文中，我們首先利用離子佈植系統，以氫離子佈植於N型氮化鎵以及P型氮化鎵上，並藉由控制佈植能量與佈植劑量，使得佈植區域位於氮化鎵薄膜內，其佈植條件為10KeV/1×1012cm-2、10KeV/5×1012cm-2、10KeV/5×1013cm-2；接著分別以500℃、600℃、700℃溫度在氮氣環境下進行熱處理製程，熱處理時間為3分鐘，探討其電流-電壓特性。 由實驗結果可知，在氫離子佈植於N型氮化鎵時，未佈植前其串聯電阻為19.45 Ω，隨著佈植濃度增加，且經過熱處理後，串聯阻值降低，其原因為經過熱處理後，晶格被修復，進而降低N型串聯電阻；在氫離子佈植於P型氮化鎵時，未佈植前其串聯電阻為1.02×104 Ω，隨著佈植濃度增加，且經過熱處理後，串聯阻值增加，由XPS量測氫離子佈植於P型氮化鎵樣品，其結果顯示，沒有觀察到Mg-H鍵結的訊號產生，故造成P型氮化鎵阻值變大的機制，並非因為化學誘發機制產生Mg-H鍵結而形成高阻值區域，而是因為破壞誘發機制導致經過熱處理製程後，使得串聯電阻值增加。由實驗結果顯示，以佈植條件為10KeV/1×1012cm-2、10KeV/5×1013cm-2經過熱處理500℃後、10KeV/5×1012cm-2經過熱處理溫度500℃、600℃後，相較於未經過熱處理製程的樣品，可有效增加P型串聯電阻和降低N型串聯電阻。 接著利用上述製程參數同時佈植氫離子於N型氮化鎵和P型氮化鎵上，進一步探討應用一次性氫離子佈植技術於氮化鎵發光二極體元件上之光電特性研究。在氫離子佈植的條件為10KeV/1×1012cm-2、10KeV/5×1012cm-2、10KeV/5×1013cm-2經過熱處理500℃後、10KeV/5×1012cm-2經過熱處理600℃後，在20mA注入下，導通電壓相較於傳統水平式結構分別為降低0.05V(3.08V)、降低0.03V(3.10V)、增加0.02V(3.15V)、降低0.01V(3.12V)，因此可知N型氮化鎵經過氫離子佈植以及熱處理後，可以降低其導通電壓。在20mA注入下，其光輸出功率相較傳統水平式結構分別提升9.5%、15.3%、20.4%、14.8%；其功率轉換效率則分別提升10.9%、16.0%、19.2%、14.7%，其光輸出功率增加的原因為當氫離子佈植於P型氮化鎵時，會形成高阻值區域，使其有電流阻擋層的效果，去改善電流擁擠效應。 利用一次性氫離子佈植技術於發光二極體元件中，此技術不但製程步驟簡單，更可以有效改善傳統發光二極體元件之電流擁擠效應，進而提升氮化鎵發光二極體元件之發光效率。

In this study, the effect that hydrogen ion implantation has on n-type and p-type GaN layers of light-emitting diode (LED) structure was investigated. The contact resistance of the n-type implanted region is expected to be reduced, allowing the overall series resistance decreased, which allows the turn-on voltage of the entire structure to decrease. In the p-type region can increase p-type series resistance to form a current blocking layer under the p-pad to improve the current crowding effect. Using this effect, a technology for conducting one-step hydrogen ion implantation in both n-type and p-type GaN LEDs structure was developed. The optical and electrical characteristics of GaN LEDs were subsequently investigated. First, an ion implantation system was used to implant hydrogen ions in both n-type and p-type GaN layers. The implantation energy and dose were controlled to locate the implant region in the GaN surface. The implant conditions of 10KeV/1×1012cm-2, 10KeV/5×1012cm-2 and 10KeV/5×1013cm-2 were set, and the samples were subjected to heat treatment at 500℃, 600℃ and 700℃ in a nitrogen ambient for 3 mins. The effect that the current-voltage characteristics had on both types of GaN bulk was investigated. The experimental result showed that, hydrogen ion implantation on n-type GaN yielded a series resistance of 19.45 Ω compared with n-type GaN without implantation treatment. When the implant dose increased and heat treatment, the series resistance decreases. The reason for decreasing series resistance after heat treatment, was caused by the lattice fixing, which reduced the n-type series resistance. Hydrogen ion implantation in p-type GaN yielded a series resistance of 1.02×104 Ω before implantation treatment, with the implant dose increased the series resistance increased after heat treatment. X-ray photoelectron spectroscopy (XPS) was used to measure the p-type GaN samples that were hydrogen ion implanted. The results showed that no Mg-H bonds were observed. Therefore, the increase in p-type GaN series resistance was not the result of a chemical mechanism (Mg-H complexes generating high resistance), but rather caused by a damaging mechanism that increased the series resistance after implantation and heat treatment. The experimental results showed that, the samples with implanting condition of 10KeV/1×1012 cm-2 and 10KeV/5×1013cm-2 after heat treatment at 500℃, 10KeV/5×1012cm-2 after heat treatment at 500℃ and 600℃, the p-type series resistance effectively increased and the n-type series resistance effectively decreased, compared with the sample without heat treatment. Adopting the process parameters mentioned previously, technology for conducting one step hydrogen ion implantation in both n-type and p-type GaN LEDs structure, was developed to further investigate the effects that one-step hydrogen ion implantation has on LEDs structure. For samples exposed to the hydrogen ion implantation conditions of 10KeV/1×1012cm-2, 10KeV/5×1012cm-2 and 10KeV/5×1013cm-2 after heat treatment at 500℃,and 10KeV/5×1012cm-2 after heat treatment at 600℃, the turn-on voltage with a 20mA current injected into the LED samples were decreased by 0.05V (3.08V),0.03V (3.10V), increased by 0.02V (3.15V) and decreased by 0.01V (3.12V), respectively. This indicates that after hydrogen ion implantation and heat treatment, the turn-on voltage of n-type GaN can be reduced. With 20mA current injected, the light output power comparing to conventional LEDs were improved by 9.5%, 15.3%, 20.4% and 14.8%, respectively. Furthermore, the wall plug efficiency was increased 10.9%, 16.0%, 19.2% and 14.7%, respectively, compared with conventional samples. The main reason for the increased light output power was that hydrogen ion implantation in p-type GaN forms a high resistance region under the p-pad that acts as a current blocking layer, and improving the current crowding effect. Therefore, applying proposed the one-step hydrogen ion implantation technology to LEDs structure not only provides a simple process flow, but also substantially improves the current crowding effect, thereby increasing the light output power of GaN LEDs.