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

用金属有机气相外延(MOVPE)方法在GaAs衬底上生长了InGaAs层。采用渐变层作为缓冲层。在取向不同的衬底上制备了高In组分的InGaAs层，低In组分的InGaAs层获得了光滑的表面形貌。在通常生长砷化镓外延层的600℃条件下，In组分为0.5的InGaAs层表面非常粗糙。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层无镜面生长。透射电子显微镜观察表明，In组分为0.4以上的缓冲层中的失配位错不平行于衬底表面。缓冲层中的残余应变随着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，由于表面即使在小的残余应变下也会变得粗糙，因此需要厚的渐变缓冲层。这导致了高昂的成本。因此，我们研究了一种抑制表面粗化的低生长温度条件。当In组分为0.5时，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5 0 0~6 0 0℃范围内没有得到镜面。当温度从500℃降低时，表面变得光滑。在450℃时，获得了镜面。横截面电子显微镜证实，InGaAs层的顶层含有少量的线状位错。缓冲层中的失配位错平行于界面。光致发光(PL)测量显示出很强的光致发光，这意味着最上层的InGaAs层具有较高的结晶质量。

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.