DISLOCATION FREE TECHNOLOGY FOR HIGHLY LATTICE MISMATCHED HETEROEPITAXY

在硅衬底上生长砷化镓技术有望开辟光电子学的新领域。本项目旨在发展在硅衬底上生长高质量砷化镓的技术。本项目所开发的技术由两部分组成。第一部分研究了在Si衬底上用MBE制备均匀GaAs的技术。为了提高晶体质量，采用了多种缓冲层，如由非晶GaAs薄层结晶而成的GaAs缓冲层、低温外延沉积的晶体GaAs缓冲层、AlAs/GaAs双非晶缓冲层等。采用和不采用热循环退火的方法在这些缓冲层上生长GaAs外延层。采用光致发光、KOH刻蚀和原子力显微镜对GaAs层进行了评价。在这些缓冲层中，AlAs/GaAs双非晶缓冲层的效果最好。在GaAs外延生长过程中进行热循环退火，得到了位错密度为3 × 10^6/cm^2、x射线FWHM窄为145秒、光致发光强度高的薄膜。在第二部分中，利用LPE的外延横向过生长来降低位错密度。采用MBE在Si上生长的GaAs外延层作为衬底，表面涂覆SiO_2薄膜。然后在SiO_2薄膜上切出5微米宽的窄窗，作为LPE生长的种子。生长从这个窗口开始，当顶部表面的高度超过氧化层时，横向生长开始。由于氧化层阻止位错继续上一层，所以横向生长层的部分成为无位错。这已被证实，并观察到横向生长区域的位错密度急剧下降。然而，观察到相对较多的层错。综上所述，横向外延生长是在Si衬底上获得无位错砷化镓的一种很有希望的技术。少

Growth technology of GaAs on Si substrate may open new area in opto-electronics. The present project aims at developing the technology to grow high quality GaAs on Si substrate. The technology developed in this project consists of two parts. In the first part, the technology for getting uniform GaAs by MBE on Si substrate was developed. To improve the crystal quality, various kinds of buffer layers were employed, for instance, GaAs buffer layer crystallized from amorphous GaAs thin layer, crystalline GaAs buffer layer epitaxially deposited at relatively low temperature, AlAs/GaAs double amorphous buffer layer and so on. The GaAs epitaxial layer is grown on these buffer layers with and without thermal cycle annealing. The evaluation of the GaAs layer was made by photoluminescence, by KOH etching and AFM. Among these buffer layers, A Among these buffer layers, AlAs/GaAs double amorphous buffer gave the best result. When the thermal cycle annealing was made during the GaAs EPITAXIAL GROWT … More H, films with low dislocation density of 3x10^6/cm^2, narrow X-ray FWHM of 145 sec and bright photoluminescence intensity were obtained.In the second part, epitaxial lateral over growth by LPE is employed to reduce the dislocation density. GaAs epitaxial layer grown by MBE on Si is used as a substrate and the surface is coated by SiO_2 film. Then narrow window of 5mum width is cut in the SiO_2 film and this part is used as a seed for the LPE growth. The growth is started from this window and when the height of the top surface exceeds the oxide layer the lateral growth starts. Since the oxide layer prevent the dislocation to continue the above layer, the part of laterally grown layer becomes dislocation free. This has been confirmed and drastic decrease of dislocation density in the laterally grown region was observed. However, relatively large number of stacking faults was observed. In conclusion, lateral epitaxial growth is very hopeful technique to get dislocation free GaAs on Si substrate. Less