红外LED用GaAs单晶的垂直梯度凝固制备研究

Prepration of GaAs Single Crystal for Infrared LED by Vertical Gradient Freeze Technology

GaAs单晶是当前光电子器件的主要衬底材料之一,在红外LED中有着重要应用。但杂质浓度高、迁移率低等缺点会严重影响红外LED器件性能。为生产出低杂质浓度、高迁移率、载流子分布均匀、高利用率的红外LED用掺硅垂直梯度凝固(VGF)法GaAs单晶,本文研究了热场分布、合成舟和炉膛材质、工艺参数对单晶的成晶质量、杂质浓度、迁移率、载流子分布的影响。利用CGSim软件对单晶生长热场系统进行数值模拟研究,温区一至温区六长度比例为8∶12∶9∶5∶5∶7时,恒温区达到最长,位错密度达到1 000 cm^(-2)以下,成晶率达到85%。采用打毛石英合成舟进行GaAs合成,用莫来石炉膛替代石英炉膛,可以获得迁移率整体高于3 000 cm^(2)/(V·s)的GaAs单晶,满足红外LED使用要求。对单晶生长工艺参数展开研究,采用提高头部生长速度、降低尾部生长速度的方式提高单晶轴向载流子浓度均匀性,头尾部载流子浓度差降低33%,尾部迁移率从2 900 cm^(2)/(V·s)提高到3 560 cm^(2)/(V·s)。单晶有效利用长度提高33%,单晶利用率达到75%,大幅降低了原料损耗成本。

GaAs single crystal is one of the main substrate materials for optoelectronic devices, and has important applications in infrared LED. However, its high impurity concentration and low carrier mobility seriously restrict the performance of infrared LED devices. To obtain silicon doped GaAs single crystals prepared by vertical gradient freeze(VGF) method with low impurity concentration, high mobility, uniform carrier distribution and high utilization ratio, the influences of thermal field distribution, materials of synthetic boat and furnace, and process parameters on crystal quality, impurity concentration, mobility and carrier distribution of single crystal were studied in this paper. CGSim software was used to conduct numerical simulation research on the thermal field system of single crystal growth thermal field. When the length ratio from temperature zone 1 to temperature zone 6 is 8∶12∶9∶5∶5∶7, the constant temperature zone reaches the longest, the dislocation density is below 1 000 cm^(-2), and the crystallization rate reaches 85%. With GaAs polycrystalline synthesized by roughening quartz synthesis boat, and the mullite furnace replacing the quartz furnace, GaAs single crystals with overall mobility higher than 3 000 cm^(2)/(V·s) were obtained. The process parameters of single crystal growth were studied. The axial carrier concentration uniformity of single crystal is improved by increasing the head pulling speed and decreasing the tail pulling speed, by which the carrier concentration difference between the head and tail is reduced by 33%, and the tail mobility increase from 2 900 cm^(2)/(V·s) to 3 560 cm^(2)/(V·s). The effective utilization length of single crystal gains increase by 33%, and the utilization rate of single crystal reaches 75%, which greatly reduces the raw material consumption cost.