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| 題名: | 氮化鋁鎵/氮化鎵蕭基二極體與氮化鋁銦/氮化鎵場效電晶體之磊晶成長、元件製作與特性探討;Growth, Fabrication and Characterization of AlGaN/GaN Schottky Diodes and AlInN/GaN Field-Effect Transistors |
| 作者: | 李庚諺;Lee,Geng-Yen |
| 貢獻者: | 電機工程學系 |
| 關鍵詞: | 氮化鎵;氮化鋁;氮化鋁銦;氮化鋁鎵;蕭基二極體;場效電晶體 |
| 日期: | 2015-12-30 |
| 上傳時間: | 2016-01-05 19:26:16 (UTC+8) |
| 出版者: | 國立中央大學 |
| 摘要: | 本論文的內容主要為高功率氮化鎵蕭基二極體以及高電流密度氮化鋁銦電晶體之磊晶與元件開發。在高壓氮化鎵蕭基二極體方面，高阻值複合式氮化鋁鎵/氮化鎵(AlGaN/GaN)緩衝層結構被成功的應用於結構中，文中並透過數個具有不同線缺陷密度之磊晶試片，完整的探討元件特性與線缺陷密度的相關性。在電極距離為30 μm下，蕭基二極體可達到一個低的開啟電阻為7.9 mΩ-cm2，高崩潰電壓為3,489 V，以及於2000 V逆偏壓下的漏電流小於0.2 μA等優越特性，並使元件的評量因子值達到1.54 GW/cm2。透過X-ray、浸蝕點密度、以及穿透式電子顯微鏡的量測分析，此優異特性可歸功於材料中形成的低密度螺旋狀線缺陷，以及高密度的刃狀線缺陷型態。
為了更深入的分析元件的漏電與暫態特性，不同的測試元件被設計出來分析表面與緩衝層漏電流；此外，從電容電壓量測中可觀察刃狀缺陷捕捉電子的效應，發現大量的電子在初始狀態下就已占據材料中的深層缺陷能階而形成固定電荷。再進一步利用模擬軟體驗證元件的現象，發現具有高缺陷密度的結構確實具有較佳的崩潰電壓特性，因此可成功的驗證材料中刃狀缺陷密度對於元件崩潰電壓有正向的影響。
在動態電阻量測方面，將元件於逆偏壓下加壓一小段時間後再快速切換至導通狀態，可觀測其電阻對時間的關係，結果顯示即使具高刃狀缺陷密度的元件也不具有動態電阻衰化的現象。最後在元件的逆向回復切換特性方面，元件在室溫下具有一個低的逆向回復時間為17 ns，且在高溫150度C下的逆向切換波型與室溫下幾乎相同，這些特性再次顯示出論文中所展示的氮化鎵蕭基二極體具有極優異的特性，其評量因子超越了傳統的矽元件，特別在高溫的表現更是如此，也證實了氮化鎵蕭基二極體應用於低損耗開關電路應用中的高度潛力。
另一方面，本論文提出了具高電流密度之氮化鋁銦電晶體 (AlInN HEMTs)磊晶與元件製程開發。一開始透過理論計算先了解氮化鋁銦材料的極化強度，二維電子氣濃度等特性，並了解合金散射(alloy scattering)在此材料中的影響。在磊晶方面，為了降低電晶體結構中載子的合金散射，結構中必須加入一層氮化鋁二元化合物作為中間層，此高能隙材料可阻擋二維電子氣之分布延伸進入氮化鋁銦位障層中。在改善磊晶材料品質後，試片的表面平坦度可降低至0.738 nm，並在不犧牲二維電子氣濃度為2.13×1013 cm-2的情況下，氮化鋁銦電晶體的電子遷移率可被提升至1360 cm2/V-s，因而成功的達成低通道片電阻值為215 ohm/sq的特性。在歷史文獻比較中，此矽基板上成長的氮化鋁銦材料特性為目前領先成果之一。
在氮化鋁銦電晶體製作方面，本文討論了一系列具有不同氮化鎵表面披覆層厚度之試片，其披覆層厚度分布為0 nm至26 nm。元件的崩潰電壓、電子遷移率、開啟後電阻、以及動態電阻等特性都隨著披覆層厚度增加而有所提升。其中具有13 nm披覆層厚度的金屬-絕緣層-半導體場效電晶體(MIS-HEMTs)可將崩潰電壓由無披覆層的530 V提升至675 V，而詳細的動態電阻研究也指出較厚的氮化鎵披覆層可有效的降低氮化鋁銦電晶體的動態電阻值，此特性的改善歸因於氮化鎵表面披覆層除了可降低表面電場值，也可提升表面能帶以避免電子於高截止偏壓下進入氮化鋁銦位障層中被缺陷捕捉之故。論文中的優異特性展示了氮化鋁銦/氮化鎵電晶體在現代功率元件中的高度潛力，並且說明了此材料於功率元件應用的可行性。;In this dissertation, the growth mechanisms and device characteristics of AlGaN/GaN-based Schottky barrier diodes (SBDs) with a high breakdown voltage and the AlInN-based high electron mobility transistors (HEMTs) with a high current density have been studied. For the high-voltage GaN SBDs, devices are fabricated on a composite AlGaN/AlN buffer layer with different threading dislocation (TD) densities. The correlation between TDs and the device characteristics could be well linked. The SBDs with an anode-to-cathode distance (LAC) of 30 μm exhibit a low on-state resistance (Ron) of 7.9 mΩ-cm2, a high breakdown voltage (VB) of 3,489 V, and a low leakage current of less than 0.2 μA at -2,000 V, which lead to a high figure-of-merit of 1.54 GW/cm2. Based on the x-ray diffraction, etch pit density, and transmission electron microscopy (TEM) measurements, high breakdown characteristics of the SBDs are attributed to low screw-type and high edge-type dislocations in the AlGaN/GaN buffer layer.
Several measurement are implemented for the in-depth analysis. The surface and buffer leakage current could be recognized successfully by the designed test devices. From capacitance-voltage (C-V) measurement, a large amount of initial occupied fixed charges at zero bias are recognized in the material, demonstrating the trapping effect by the edge-type dislocations. Moreover, the simulation results with the associated trap densities in the structures correlate well with the experimental results, which evidences the VB of the device is associated with their edge-type TDs in the material.
From dynamic Ron measurement, no obvious charging effect as well as the dynamic Ron degradation is observed during the reverse voltage bias. At room temperature (RT), the SBD with a high edge-type dislocation density show a low reverse recovery time of 17 ns. Under a high temperature of 150 oC, the switching curve of the device almost remain the same as RT’s performance. These performances are comparable to the reported GaN-based SBDs and outperform their silicon counterpart especially at high temperature, which demonstrate their potential for high-power low-loss switching circuits.
For the development of AlInN HEMTs, the theoretical calculation of polarization and the growth conditions have been systematically studied. The alloy scattering rate with arbitrary unit could be estimated in both AlGaN and AlInN alloys in comparison. In order to reduce alloy scattering in GaN-based HEMTs, a binary material as an AlN spacer layer with wide bandgap inserting between AlGaN/GaN or AlInN/GaN interface is essential to prevent the electron profile from extending into the barrier layer. The epitaxy growth conditions of the AlInN HEMTs are well investigated. After improving the crystal quality of AlInN HEMTs, the improved surface root-mean-square (RMS) roughness of 0.738 nm and the increased mobility to 1360 cm2/V-s without sacrificing its two-dimensional electron gas (2DEG) density (2.13×1013 cm-2) are successfully demonstrated, leading to a very low sheet resistance (Rsh) of 215 ohm/sq. The benchmark shows the mobility value is one of the best results among AlInN HEMTs grown on silicon substrate.
On the other hand, the electrical characteristics of a series of AlInN HEMTs with GaN cap layer thicknesses ranging from 0 to 26 nm have been investigated. The breakdown voltage, mobility of two-dimensional electron gas, on-state resistance, and dynamic Ron of the HEMTs are improved by increasing the cap layer thickness. The off-state breakdown voltage of AlInN MIS-HEMTs is increased from 530 to 675 V by adding a 13-nm-thick GaN cap layer. Detailed studies on the dynamic Ron of the AlInN HEMTs indicate that the GaN cap layer can greatly reduce the dynamic Ron ratio, and that the devices with a 26-nm-thick GaN cap layer can achieve a dynamic Ron ratio comparable to that of AlGaN MIS-HEMTs. These improved electrical characteristics are attributed to the GaN cap layer, which not only reduces the surface E-field but also raises the conduction band of the barrier layer and effectively prevents electrons from being trapped in the AlInN barrier and above. These results show the talents of AlInN/GaN HEMTs for modern power electronic devices. |
| 顯示於類別: | [電機工程研究所] 博碩士論文
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