Realization of homogeneous dislocation distribution in a buffer layer by self-organization

采用金属有机气相外延（MOVPE）技术在GaAs衬底上生长InGaAs层。采用分级层作为缓冲层。在错取向的GaAs衬底上制备了高In组成的InGaAs层，低In组成的InGaAs层表面形貌光滑。在通常生长GaAs外延层的600℃下，In含量为0.5的InGaAs层表面极为粗糙。在600℃左右，通过优化生长条件（如气体流速），可获得In含量为0.5的InGaAs层无镜面。透射电镜（TEM）观察表明，在in组成为0.4时，缓冲层中的错配位错并不平行于GaAs衬底表面。缓冲层残余应变随in成分的增加而增加。高温生长可以减少外延层中的残余应变。但在高温下，即使在很小的残余应变下，表面也会变得粗糙，因此需要一层厚的渐变缓冲层。这导致了高成本。因此，我们研究了低生长温度条件来抑制表面粗化。对于In含量为0.5的InGaAs层，当温度从600℃降低时，表面变得粗糙。降解被发现是由于高残余应变和相分离。在500 ~ 600℃范围内无镜面。当温度从500℃开始降低时，表面变得光滑。在450℃下得到镜面。透射电镜证实，顶部InGaAs层存在少量螺纹位错。缓冲层中的错配位错平行于界面。光致发光（PL）测量显示出较强的PL发射，这意味着顶部InGaAs层具有较高的晶体质量。

InGaAs layers have been grown on GaAs substrates by metalorganic vapor phase epitaxy (MOVPE). Graded layers were used as buffer layers. InGaAs layers with high In composition were prepared on misoriented GaAs substrates where a smooth surface morphology was obtained for low In composition InGaAs layers. At 600 ℃ where GaAs epitaxial layers were usually grown, an extremely rough surface was obtained for an InGaAs layer with In composition of 0.5. Around 600 ℃, no mirror surface was achieved for InGaAs layers with In composition of 0.5 by optimizing growth conditions such as gas flow rates. Cross sectional TEM (transmission electron microscopy) observation showed that misfit dislocations in the buffer layer over In composition of 0.4 were not parallel to the surface of the GaAs substrate. Residual strain in the buffer layer increased with the In composition.High temperature growth would reduced a residual strain in an epitaxial layer. But at high temperature, a thick graded buffer layer is required because the surface becomes rough even under a small residual strain. This leads to a high cost. Therefore we investigated a low growth temperature conditions to suppress the surface roughening. When temperature was decreased from 600 ℃ for InGaAs layers with In composition of 0.5, the surface became rough. The degradation was found to be due to a high residual strain and a phase separation. No mirror surface was obtained at between 500 and 600 ℃. As the temperature was decreased from 500 ℃, the surface was found to become smooth. A mirror surface was achieved at 450 ℃. Cross sectional TEM confirmed that the top InGaAs layer contained a few threading dislocations. Misfit dislocations in the buffer layer ran parallel to the interface. Photoluminescence (PL) measurement showed a strong PL emission, which meaned a high crystalline quality for the top InGaAs layer.