| 摘要: | 在氮化鎵二極體中，缺陷的存在使得發光二極體的量子效率下降，本研究論文指出氮化鎵發光二極體的缺陷密度為：2.17×10-9 cm-2、3.636×10-9 cm-2、4.654×10-9 cm-2時發光效率分別是20.546 %、19.563%、16.785%，故建立一套精準快速的缺陷量測系統在現今半導體固態照明產業是非常重要的，然而現今的缺陷量測系統有諸多限制，如XRD只適用在晶圓尺寸下進行量測，而TEM及EPD計算則是破壞性量測，會造成元件損壞及浪費，本研究乃建立一套以分析氮化鎵發光二極體元件受力以及電場作用後的滯彈行為作為缺陷量測系統，
滯彈行為乃是固體因內部缺陷導致材料受力後的形變並非瞬時響應，雖然對於塊材的滯彈行為已有完善的討論系統，但是對於薄膜材料以及此行為對半導體元件效能的影響卻缺少相關研究及探討。本論文係研究氮化鎵發光二極體內部缺陷的數量對於其材料受力後的滯彈行為之影響，並希望能建立以分析氮化鎵滯彈行為的晶片缺陷量測系統。本研究將以熱應力、壓電應力、機械應力三種方法給予晶片應力。當施加正電場於GaN LED晶片時順向偏壓值因為能階傾斜程度改變而下降，然而移除電場之後，順向偏壓值並不會立刻回復，而是隨時間逐漸改變。我們認為這乃是滯彈行為導致晶片在受到電場或應力作用後會有延遲形變的現象。我們分別將晶片施予逆偏壓-0.5 V以及將晶片溫度升高至100 oC，使能階傾斜程度平緩造成有效能隙變大進而使順向偏壓上升，提高負偏壓至-1 V則順向偏壓上升量更大，但是負偏壓過大時則有可能讓能階傾斜程度再次變大，使順向偏壓值不增反減。分析偏壓值與時間的關係後得到滯彈行為的兩個重要參數，遲豫特徵時間τ與滯彈形變量Umax，我們將氮化鎵發光二極體以磷酸蝕刻表面後計算晶片的缺陷密度，發現缺陷密度越高的氮化鎵發光二極體晶片亦有較高的Umax與τ值，且缺陷密度與滯彈形變量為線性關係，故可證明滯彈行為乃是因為缺陷的存在而造成，另一方面則代表利用滯彈行為的分析來預測氮化鎵發光二極體是可行的。因為晶片缺陷密度與滯彈形變量為線性關係，因此我們可以藉由量測氮化鎵發光二極體的滯彈行為得知其內部缺陷多寡，缺陷密度與滯彈型變所導致的順向偏壓值最大變化量的關係為Vf,max=0.00168×Ddis+0.00329，其中Vf,max為滯彈形變所導致的順向偏壓值最大變化量，Ddis為差排密度。
;Defects decline the light output efficient and life time of GaN-based LED. In our study, as the defect density of device is 2.17×10-9 cm-2, 3.636×10-9 cm-2, 4.654×10-9 cm-2, respectively, the external quantum efficient is 20.546 %, 19.563%, 16.785%, respectively. To establish a high accuracy and convenient defect measuring system is necessary. However, the defect measuring methods that commonly used have many limits. For example, XRD spectrum is only suitable for wafer size sample. TEM and EPD evaluating method are destructive measurement that waste many sample and cost much time. We established a defect measuring method in this study by analyzing anelasticity behavior of GaN-based LED after applying stress or external electric field.
Defects develop Anelasticity behavior in solid. It causes the strain delay-responding after applying stress on material. Although there has complete study about anelasticity behavior of bulk material, the research of thin-film materials and the influence of semiconductors is lack. In this study, the anelasticity of the GaN layer in the GaN light-emitting-diode device was discussed. And, establish defect measurement system can be established. The studied chip was applied by thermal stress, piezoelectric stress, and external stress. The present results show that the decrease of forward-voltage of GaN LED is due to the degree of energy-level change as forward external electric field applied. After removing external electric field, the forward voltage increase with time. We found that the increment of the forward-voltage with time attributes to the delay-response of the piezoelectric fields (internal electrical fields in GaN LED device). We applied -0.5 V reverse bias and heat the chip to 100 oC, respectively. Thus, the forward voltage increases gradually due to the energy-level in GaN LED is flattened with time by thermal stress and external electric field. Furthermore, reverse bias (-1 V) flatten the energy level much more, so, the forward voltage enhancement is higher. As -5 V reverse bias is applying on the GaN LED, the voltage dropped due to the higher reverse bias tilted the energy-level in GaN LED again. Using the correlation of strain-piezoelectric-forward voltage, a plot of strain of the GaN layer against time can be obtained by measuring the forward-voltage of the studied GaN LED against time. The key anelasticity parameter, characteristic relaxation time τ, and anelastic strain Uan of the GaN would be analyzed by the curves of the thermal strain in GaN epi-layers versus time. For estimating the dislocation density, the studied GaN LED chips were etched by H3PO4 in 260 oC. The etching pits on GaN LED after H3PO4 reacted were calculated. GaN LED chip with higher dislocation density has higher τ and Umax, furthermore, the dislocation density and anelastic strain is linear relation. The results show the anelasticity behavior is attributed by defect. In other side, it is possible for establishing a defect measurement system by analyzing anelasticity behavior of GaN LED. The relation of defect density and anelastic strain can be expressed as Vf,max=0.00168×Ddis+0.00329. Vf,max is the forward-voltage difference induced by anelastic strain of GaN-based LED. Ddis is the density of dislocation in GaN-based LED. |
