Development of reactively controlled super-sonic nozzle beam epitaxial growth technique

我们发展了一种被称为“超音速束外延”(SSBE)的生长技术。利用这项技术，我们利用高速RHEED和RD，在毫秒范围内对生长表面的动态过程进行了现场观测和了解，并通过设置脉冲宽度，实现了对生长速率的精确控制，达到每个脉冲1/10个单层。此外，我们还成功地利用超音速束源控制了表面反应过程。结果表明，采用超音速束源可以大大抑制晶体生长过程中碳杂质的掺入，使晶体中的碳浓度比通常的低两个数量级。宽带隙GaN和相关的III-V氮化物材料在光学器件，特别是蓝光和紫外光发光二极管(LED)和激光二极管(LDS)中显示出很强的应用潜力。人们已经通过MOCVD、MBE等各种生长技术来生长这类材料。我们成功地将SSBE和GSMBE两种技术结合起来，用于GaN量子点结构的制备。我们使用硅作为“抗表面活性剂”来制备GaN点，其中以甲基硅烷(CH_3SiH_3)作为硅源。据报道，CH3SiH3在800ﾟC以上开始分解，由于GSMBE生长通常是在相对较低的温度下进行的，因此很难使用。但利用SSBE技术克服了这一困难，因为高能量的源束被认为促进了CH_3SiH_3分子分解成Si原子。结果，利用GSMBE成功地制备了GaN量子点结构。

We developed the growth technique which is called "supersonic beam epitaxy" (SSBE). Using the technique, we in-situ observed and understood dynamic processes of GaAs growing surface in a milisecond range by means of high-speed RHEED and RD.Precise control of the growth rate to 1/10 monolayr per pulse was also achieved simply by arrangeing the pulse width. Furthermore, we succeeded in the control of surface reaction processes by using supersonic beam source. As a result, by using supersonic beam source, incorporation of carbon inpurities into the crystal during the growth was greatly suppressed and the concentration of carbon in the GaAs crystal is two-order less than that using usual one. All these indicates that the technique is useful and hopeful for the future applications.Wide band-gap GaN and related III-V nitride materials have shown a strong potential for use in optical devices, especially blue and ultraviolet light emitting diodes (LEDs) and laser diodes (LDs). Many efforts have been done to grow such kind of materials by various growth techniques, such as MOCVD,MBE and etc. We successfully combined two techniques namely SSBE and GSMBE together, for the fabrication of GaN quantum dot structures. We used Si as an "anti-surfactant" for the GaN dot fabrication, where methylsilane (CH_3SiH_3) was used as a Si source. Since it was reported that CH_3SiH_3 begins to decompose above 800ﾟC,it is difficult to use it because usually GSMBE growth is carried out at a relatively low temperature. But by using SSBE technique, this difficulty was overcome since high energy of the source beam is thought to enhance the decompositon of the CH_3SiH_3 molecules into Si atoms. As a result, GaN quantum dot structures were successfully fabricated by GSMBE.