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通过调整非故意掺杂氮化镓层的厚度,分析氮化镓基LED外延生长过程中应力的演变行为,以控制外延片表面的翘曲程度,从而获得高均匀性与一致性的外延片。由于衬底与外延层之间的热膨胀系数差别较大,在生长温度不断变化的过程中,外延片的翘曲状态也随之改变。在n型氮化镓生长结束时,外延片处于凹面变形状态。在随后的过程中,外延薄膜“凹面”变形程度不断减小,甚至转变为“凸面”变形,所以n型氮化镓生长结束时外延片的变形程度会直接影响多量子阱沉积时外延片的翘曲状态。当非掺杂氮化镓沉积厚度为3.63μm时,外延片在n型氮化镓层生长结束时变形程度最大,在沉积多量子阱时表面最为平整,这与PLmapping测试所得波长分布以及标准差值最小相一致。通过合理控制非故意掺杂氮化镓层的厚度以调节外延层中的应力状态,可获得均匀性与一致性良好的LED外延片。
By adjusting the thickness of the unintentionally doped GaN layer, the evolution of the stress during the epitaxial growth of gallium nitride based LED was analyzed to control the degree of warpage on the surface of the epitaxial wafer to obtain high uniformity and uniformity of the epitaxial wafer. Due to the large difference in thermal expansion coefficient between the substrate and the epitaxial layer, the warping state of the epitaxial wafer also changes during the process of changing the growth temperature. At the end of n-type gallium nitride growth, the epitaxial wafer is in a concave deformed state. In the subsequent process, the degree of deformation of the epitaxial film “concave ” decreases and even changes to “convex ” deformation, so the degree of deformation of the epitaxial wafer at the end of n-type gallium nitride will directly affect the deposition of multiple quantum wells When the wafer warpage state. When the thickness of non-doped gallium nitride deposition is 3.63μm, the epitaxial wafer has the most deformation at the end of growth of n-type gallium nitride layer and the most flat surface when depositing MQWs, which is in agreement with the wavelength distribution and standard deviation of PLmapping test The minimum value consistent. By reasonably controlling the thickness of the unintentionally doped GaN layer to adjust the stress state in the epitaxial layer, uniform and consistent LED epitaxial wafers can be obtained.