Plasma-assisted molecular beam epitaxy of Al(Ga)N layers and quantum well structures for optically pumped mid-UV lasers on c-Al2O3
Plasma-assisted molecular beam epitaxy of Al(Ga)N layers and quantum well structures for optically pumped mid-UV lasers on c-Al2O3
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DOI：
10.1088/0268-1242/29/8/084008
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发表时间：
2014-08-01
影响因子：
1.9
通讯作者：
Jmerik, V. N.
中科院分区：
文献类型：
--
作者：
Ivanov, S. V.;Nechaev, D. V.;Jmerik, V. N.
本文报道了在c-蓝宝石上富al AlGaN薄膜和量子阱异质结构的等离子体辅助分子束外延的新方法，使我们能够制造出发射在中紫外光谱范围（258-290 nm）的低阈值光泵浦分离约束异质结构激光器，其阈值功率密度低于600 kW cm（-2）。该缓冲结构可将螺旋型和边缘型的近表面螺纹位错密度分别降低至1.5 x 10(8)和3x 10(9) cm(-2)，并改善表面形貌（在3x3 mum（-2）区域的rms < 0.7 nm）。它包括在C - al2o3上高温（780℃）迁移增强外延生长（30-70）nm厚的AlN成核层，然后在富金属条件下在al通量调制模式下生长2 μ m厚的AlN缓冲层，并包含在富n条件下生长的几个（最多6个）超薄（类似于3 nm） GaN中间层。在AlN缓冲层上生长的AlGaN单量子阱异质结构中进行适当的应变工程，即使在最短波长（258 nm）处，也可以保持自发发射和受激发射的优势TE偏振。在289 nm处，单量子阱激光结构的受激辐射阈值功率密度低至150 kW cm（-2）。
This paper reports on novel approaches developed for plasma-assisted molecular beam epitaxy of Al-rich AlGaN epilayers and quantum well heterostructures on c-sapphire, which allowed us to fabricate low-threshold optically-pumped separate confinement heterostructure lasers emitting in the mid-UV spectral range (258-290 nm) with the threshold power density below 600 kW cm(-2). The optimum buffer structure has been developed which provides lowering the near-surface threading dislocation density down to 1.5 x 10(8) and 3 x 10(9) cm(-2) for screw and edge types, respectively, and improving the surface morphology (rms < 0.7 nm at the area of 3x3 mu m(-2)). It comprises the high-temperature (780 degrees C) migration enhanced epitaxy growth of a (30-70) nm thick AlN nucleation layer on c-Al2O3, followed by a 2 mu m thick AlN buffer grown under the metal-rich conditions in the Al-flux modulation mode and containing several (up to 6) ultra-thin (similar to 3 nm) GaN interlayers grown at N-rich conditions. Proper strain engineering in AlGaN single quantum well heterostructure grown atop of the AlN buffer layer enables one to preserve dominant TE polarization of both spontaneous and stimulated emission even at shortest obtained wavelength (258 nm). The threshold power density of stimulated emission as low as 150 kW cm(-2) at 289 nm for a single quantum well laser structure has been demonstrated.