GaN基发光二极管（Light-Emitting-Diode，LED）在显示和照明领域具有重要应用。但是，目前的GaN基LED主要基于极性面（c面）生长，尽管具有很高的效率，但是依然面临大电流下量子效率显著下降（Efficiency Droop）、绿光波段效率低、LED调制带宽小等瓶颈问题。通过改变生长晶面至半极性面可以降低InGaN量子阱内的自发极化和压电极化强度，提高载流子的辐射复合速率，是解决上述瓶颈问题的有效途径之一。本文提出了一种和现有极性面LED生长工艺完全兼容的低成本半极性面LED生长技术，即采用金属有机物化学气相沉积（MOCVD）技术在c面蓝宝石图形衬底上外延生长三维半极性面GaN小面，进而进行半极性面InGaN量子阱和LED的外延生长，通过对生长工艺的优化、材料光学和电学特性的表征，最终实现了半极性面LED电注入发光。论文工作取得的主要创新成果如下：（1）在蓝宝石图形衬底上实现了GaN半极性面体材料外延，得到了{101 ?1}和{112 ?2}两种半极性晶面，发现生长温度会影响半极性面的面积和二者间的面积比例，在950℃，{101 ?1}半极性面为主；在970℃，两种半极性面面积相当；图形衬底的图形排布会影响倒金字塔结构的图形排布；通过先950℃低温外延后1000℃高温外延的二步法可以进一步对半极性面的大小进行控制。（2）通过在半极性面上外延不同宽度、不同铟组分的InGaN量子阱，得到了发光波长从蓝光到绿光的一系列半极性面量子阱。发现在同一半极性面内，随着半极性面深度的增加，铟含量逐渐变小，荧光波长相应变短。利用倒金字塔结构的不均匀性，可以实现不同波长的荧光峰，得到无荧光粉的白光量子阱。（3）外延蓝光半极性面量子阱LED，其半极性面荧光波长为449nm，并对LED的光学及电学性质进行了测试分析，发现LED的量子效率在100 A/cm2时仍有峰值效率的90%以上，Droop效应得到了明显抑制。
GaN-based light-emitting diode(LED) has been widely used in display and lighting areas. The most commonly used lattice surface is {0001}, which is also known as c plane. Though it has got much progress in efficiency, GaN-based LED still suffer from efficiency Droop, Green gap and low bandwidth because of serious spontaneous polarization and piezoelectric polarization on c plane. One guaranteed method to solve these problems is growing LED on GaN nonpolar and semipolar planes, which can decrease the polarization and increase radiation recombination rate inside LED. In this work, a new kind of semipolar GaN epitaxy is used. Semipolar facets of GaN are grown on c-plane patterned sapphire substrate(PSS) through 3-dimension growth using MOCVD. Above this bulk layer, semipolar quantum wells and semipolar LED are grown. Electroluminescence is realized on semipolar quantum-well LED eventually.Firstly, two kinds of semipolar GaN facets, {101 ?1} and {112 ?2}, are grown on PSS. By applying different, the relation between semipolar and temperature is found. In low temperature, around 950℃, most surface is covered with {101 ?1}. With temperature increasing, {112 ?2} facets enlarge and {101 ?1} facets become smaller. In 970℃, both have comparable areas. The shape of GaN structure can also be affected by the shape of patterns on substrate. the area of semipolar can be controlled using two-step growth, which include a firstly 950℃ growth to form semipolar facets and a secondly 1000℃ growth to decrease that.Secondly, various photoluminescence wavelength quantum wells are grown by changing the thickness of quantum well and Indium concentration. It is found that Indium concentration decreases with the testing spot closer to the bottom of semipolar facets. Inhomogeneity of inverted pyramids is also discovered and evidences show that it is a good way to grow phosphor-free white quantum well structure.Finally, blue quantum well LED is grown on semipolar GaN structure. The wavelength of semipolar {101 ?1} quantum well is 449nm. Efficiency Droop is obviously suppressed in this semipolar LED as the external quantum efficiency(EQE) in 100A/cm2 is still more than 90% compared with the peak value.
