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

采用金属有机物气相外延（MOVPE）技术在GaAs衬底上生长了InGaAs层。梯度层用作缓冲层。在取向不良的GaAs衬底上制备了具有高In组分的InGaAs层，其中对于低In组分的InGaAs层获得了光滑的表面形貌。在通常生长GaAs外延层的600 ℃下，对于In组分为0.5的InGaAs层，获得了极其粗糙的表面。在600 ℃左右，通过优化气体流量等生长条件，In组分为0.5的InGaAs层实现了无镜面生长。横截面TEM（透射电子显微镜）观察表明，在缓冲层中的失配位错超过In组分为0.4是不平行的GaAs衬底的表面。缓冲层中的残余应变随In组分的增加而增加，高温生长会降低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，因此需要厚的梯度缓冲层。这导致高成本。因此，我们研究了一种低生长温度条件来抑制表面粗糙化。In组分为0.5的InGaAs层，当温度从600 ℃降低时，表面变得粗糙。降解被认为是由于高的残余应变和相分离。在500 - 600 ℃之间没有获得镜面。当温度从500 ℃降低时，发现表面变得光滑。在450 ℃下获得镜面。横截面TEM证实，顶部InGaAs层包含一些穿透位错。缓冲层中的错配位错平行于界面。光致发光（PL）测量显示出强的PL发射，这意味着顶部InGaAs层的高结晶质量。

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.