Korea Basic Science Institute, Daejeon, 169-148, Republic of Korea.
Ecole Polytechnique Fédérale de Lausanne, Laboratory of Semiconductor Materials, Lausanne, 1015, Switzerland.
Sci Rep. 2017 Aug 17;7(1):8587. doi: 10.1038/s41598-017-08905-y.
We investigate the stress evolution of 400 µm-thick freestanding GaN crystals grown from Si substrates by hydride vapour phase epitaxy (HVPE) and the in situ removal of Si substrates. The stress generated in growing GaN can be tuned by varying the thickness of the MOCVD AlGaN/AlN buffer layers. Micro Raman analysis shows the presence of slight tensile stress in the freestanding GaN crystals and no stress accumulation in HVPE GaN layers during the growth. Additionally, it is demonstrated that the residual tensile stress in HVPE GaN is caused only by elastic stress arising from the crystal quality difference between Ga- and N-face GaN. TEM analysis revealed that the dislocations in freestanding GaN crystals have high inclination angles that are attributed to the stress relaxation of the crystals. We believe that the understanding and characterization on the structural properties of the freestanding GaN crystals will help us to use these crystals for high-performance opto-electronic devices.
我们研究了通过氢化物气相外延（HVPE）和 Si 衬底的原位去除生长的 400μm 厚的自由 standing GaN 晶体的应力演变。通过改变 MOCVD AlGaN/AlN 缓冲层的厚度，可以调整生长 GaN 时产生的应力。微拉曼分析表明，自由 standing GaN 晶体中存在轻微的拉伸应力，并且在 HVPE GaN 层的生长过程中没有应力积累。此外，证明 HVPE GaN 中的残余拉伸应力仅由 GaN 和 N 面 GaN 之间的晶体质量差异引起的弹性应力引起。TEM 分析表明，自由 standing GaN 晶体中的位错具有较高的倾斜角，这归因于晶体的应力松弛。我们相信，对自由 standing GaN 晶体的结构特性的理解和表征将有助于我们将这些晶体用于高性能光电设备。
