SiC基高速、高红外响应度SiC/Ge异质结光电二极管的研究

Due to the wide bandgap, SiC is only sensitive to ultraviolet light, which essentially limits its application for detection of visible and infrared light. To realize light-operation of the SiC power devices, Ge/SiC heterojunction is adopted to develop the high infrared responsivity and high-speed SiC/Ge photodiode on SiC, in which Ge of narrow bandgap is used as an infrared light-absorption layer. This project will include the following interlinked components：1) theoretical analyzing influence of the SiC/Ge heterojunction structural parameters on near-infrared photoelectrical properties, obtaining the optimized model ; 2) Establishing and optimizing the preparation process of the SiC/Ge heterojunction. On one hand, controlling the preferred orientation of the Ge films on SiC; On the other hand, using Si and SiGe with varying Ge content as buffer layers to relieve the SiC/Ge lattice-mismatch strain further; 3) observing the SiC/Ge heterojunction interface and the Ge films at the atomic level. Based on the characterization results, using molecular dynamics method to investigate the mechanisms of Ge film growth and the formation of structural defects . 4) Using the optimized model to fabricate SiC/Ge heterojunction photodiode, optimizing the key parameters such as photoelectrical sensitivity and response time, obtaining high infrared responsivity and high-speed SiC/Ge heterojunction photodiode.

由于SiC材料禁带宽，SiC光控器件只受控于紫外光源。我们使用窄带隙的Ge材料作为红外光敏层，与SiC构成异质结，开发红外高响应、响应速度快的SiC基异质结光电二极管，以期实现常用通信光源对SiC功率器件的直接光控。本项目具体内容包括：计算机仿真各种结构SiC/Ge异质结的结构参数对器件近红外光电特性的影响，得出优化器件模型；建立并优化SiC/Ge异质结制备工艺，提高晶体质量。一方面，控制Ge薄膜的择优生长取向，另一方面，利用Si和组分渐变的Ge层作为缓冲层缓解SiC/Ge异质结失配应力；对SiC/Ge异质结界面和Ge薄膜进行原子级观察，基于观察结果，利用分子动力学方法探索Ge薄膜生长和缺陷形成的机理；利用优化器件模型，制备SiC/Ge异质结光电二极管，优化光电灵敏度、响应时间等关键参数，以得到红外高响应度、高响应速度的SiC/Ge异质结光电二极管。

由于SiC材料禁带宽，SiC光控器件只能受控于紫外光源。我们使用窄带隙的Ge材料作为红外光敏层，与SiC构成异质结，开发近红外高响应的SiC基异质结光电二极管，以期实现常用通信光源对SiC功率器件的直接光控。本项目主要研究内容及结果如下：.1. 采用计算机仿真SiC/Ge异质结的结构参数对器件近红外光电特性的影响，得出优化器件模型。n-SiC/p-Ge异质结导带底突变为0.28eV，价带顶突变为2.06eV，主要载流子为电子；当p-Ge、n-SiC掺杂浓度为1×1015cm-3和1×1017cm-3，厚度为2.5μm和300μm时，在0.1W/cm2近红外光照下，异质结光电流密度可达43.1mA/cm2；.2. 使用化学气相沉积法制备SiC/Ge异质结，控制Ge薄膜的择优生长取向。在6H-SiC(0001)上，750℃-975℃的区间内，成功制备了具有明显岛状特征的Ge薄膜。当源气体GeH4:H2=20:200SCCM，温度为850℃，压力为440Pa时，Ge薄膜在[111]晶向高度择优，晶体质量较优；.3. 基于XRD、HRTEM的表征，建立了SiC/Ge异质结界面模型。SiC/Ge异质结生长遵循域匹配模式。SiC(001)/Ge(111)异质结界面取向为SiC[110]//Ge[01-1]，SiC/Ge原子比为4:3，残余失配2.7%。SiC(001)/Ge(110)异质结界面取向转变为SiC[010]//Ge[1-10]，在SiC[210]Ge[001]晶向，SiC/Ge原子比为1:1，失配增至-5.7%；.4. 制备了n+-6H-SiC/p-Ge异质结光电二极管。暗状态下，该异质结器件具有显著的整流特性，±3V时的整流比超过4.0×103。当近红外光功率为0.1W/cm2时，异质结具有明显的光电响应，光生电流为0.147μA/cm2；.5. 利用湿法转移法制备了SiC/Ge/石墨烯双异质结。该异质结在可见光-近红外区都有明显吸收，透过率低于15%。利用该结构有望提高SiC基异质结的近红外光电性能；.综上所述，本项目系统建立了气相外延法制备SiC/Ge异质结的工艺方法，初步实现了近红外光控的SiC/Ge异质结器件，获得了SiC近红外光控开关器件的核心技术。