三族氮化物(氮化銦、氮化鎵、氮化鋁)在光電與電子元件方面為具有相當應用潛力的材料。為了正確的設計三族氮化物元件,適當的了解其本質電子特性是相當重要的。然而,三族氮化物的天然晶格結構是烏采結構(wurtzite structure)。烏采結構會在三族氮化物的表面與介面產生強烈的巨觀極化場,包含自發極化場(spontaneous polarization)與壓電場(piezoelectric polarization)。因此,成長在一般極化方向的三族氮化物磊晶薄膜其電性與光性與成長在非極化方向的薄膜有相當大的不同。 本文對於三族氮化物其電子特性與極性的關聯做了一系列的研究。在第一章,我們會簡單的介紹研究三族氮化物電子特性的背景。第二章會對於本文研究所使用的技術如同步輻射光電子能譜術(SR-PES)與光電子顯微術(SPEM/S)做介紹。第三章會對於不同成長晶面的氮化物薄膜電子特性作一系列的研究,尤其著重在氮化銦表面電荷堆積(electron accumulation)的議題上有完整的討論。接下來,我們對於決定三族氮化物異質接面的能帶排列做了完整的研究。在第四章中提到了三族氮化物異質接面的界面上因存在強大自發極化場差異造成了其價帶不連續值(valence band offset)有非對稱性。這也是為何一直到現在三族氮化物價帶不連續值的報導值一直有很大差異的原因。因此我們團隊發展了可以決定半導體能帶結構排列的技術。第五章利用截面掃描式光電子顯微術(cross-sectional scanning photoelectron microscopy, XSPEM/S)對於三族氮化物做了微區的電子結構探測。不但決定了三族氮化物的能帶結構排列,還可應用於決定氮化物的電子或電洞摻雜濃度。第六章對本論文的內容做總結與討論並指出三族氮化物未來的研究方向。希望對於未來光電與電子元件的應用有所助益。
Group-III nitride (InN, GaN, AlN, and their alloys) heterostructures are promising materials for device applications in optoelectronics and electronics. For accurate design of III-nitride devices, detailed knowledge of their intrinsic electronic properties is important. However, the natural crystalline form of group-III nitrides, the wurtzite structure, induces strong macroscopic polarization (including spontaneous and piezoelectric polarization) fields at the surface and interface. The electrical and optical properties of III-nitride epitaxial films grown in the conventional polar direction are substantially different from those grown in nonpolar directions. This is a systematic study of the relationship between the electronic properties and polarity of group-III nitrides. Chapter 1 introduces the research background for group-III nitrides. Chapter 2 describes related experimental techniques to probe the electronic properties of III-nitrides. Chapter 3 presents studies of the electronic properties of III-nitride surfaces with any crystal orientations, with a special focus on electron accumulation at InN surfaces. The band lineup of group-III nitride heterojunctions is also an important topic for this thesis. Chapter 4 shows the asymmetric valence band offset in III-nitride polar heterojunctions because of spontaneous polarization discontinuities among III-nitrides, explaining why the reported valence band offsets in III-nitrides still show large discrepancies to date. For this reason, our group developed a technique, cross-sectional scanning photoelectron microscopy (XSPEM/S), to achieve the natural band lineup of semiconductors. Using XSPEM/S, the measurement geometry and near-fully relaxed lattice structure allow for the determination of “natural” band alignments without the influence of spontaneous and piezoelectric polarization fields. Chapter 5 presents the XSPEM/S measurements for determining the band lineup of III-nitride. Additionally, this technique (XSPEM/S) can directly visualize the GaN p-n junctions without the influence of crystal polarity and other surface contaminations. Finally, Chapter 6 explains the study’s conclusions and suggests future research topics in group-III nitrides. The realization of group-III nitride semiconductors would be useful for future optoelectronic and electronic device applications.