【作者】 张永；

【导师】 康俊勇； 李成；

【作者基本信息】 厦门大学 ， 凝聚态物理， 2009， 博士

【摘要】 随着无线通信和光纤通信技术的发展与融合,对组成通信系统的光电子器件性能和成本的要求日益提高。传统的Si材料器件以其成熟的工艺技术具有高集成和低成本优势,但是由于受到Si材料自身特性和器件结构的限制,无法满足高速的要求。SiGe异质结晶体管（HBT）利用了能带工程和成熟的Si微电子工艺,频率特性得到了质的飞跃,在无线通信领域得到了广泛应用;与此同时,引入具有内部增益的SiGe异质结光晶体管（HPT）,发挥与SiGe HBT结构工艺完全兼容的优势,拓展了Si基材料和器件在光纤通信领域的应用。但是,SiGe HPT由于吸收区Ge组分和厚度受到Si衬底的限制,在光纤通信波段无法获得较高的响应度。本文以提高SiGe HBT的功率和频率特性、SiGe HPT的响应度和响应波长为目的,在SiGe HBT和HPT理论设计、材料制备和器件研制三方面开展了研究工作。取得了以下主要成果:（1）参与完成了新型国产双生长室UHV/CVD系统的安装与调试,并通过大量的生长实验优化了SiGe材料的生长条件,总结出Ge组分、生长速率和掺杂浓度随源流量、温度等条件的生长动力学规律,为SiGe HBT和HPT的制备奠定了材料基础。（2）设计并制备了工作在L波段（1～2GHz）的微波功率SiGe HBT。定量研究了Ge组分对SiGe HBT性能的影响,发现当基区Ge组分从0.20增加到0.23时,导致SiGe HBT电流增益从60提高到158。当基极为电压和电流输入时,观察到SiGe HBT分别呈现正、负两种相反的热电反馈现象,并采用电压源与电阻串联的输入方式,实现了SiGe HBT自加热特性的自补偿,解决了功率SiGe HBT自加热问题。（3）采用氧化法制备了高质量Si基和SOI基SiGe弛豫衬底,并建立了SiGe氧化动力学模型。在模型中首次引入了氧化物中应力的作用,发现并证实了SiGe氧化速率增强是由于氧气在氧化物中的扩散激活能较低所导致,修正了以往人们认为由于Ge-Ge键能比Si-Si键能更弱的观点,并合理解释了一直颇具争议的SiGe氧化自停止现象。（4）系统地研究了SiGe弛豫衬底二次外延中表面热处理方法。发现了高温脱氧时SiGe薄膜表面形成Ge岛,通过改变SiGe薄膜中的Ge组分可实现Ge岛大小和密度的调控,为制备Ge量子点提供了新的方法;而采用高温脱氢时,发现SiGe表面形成坑,通过优化脱氢温度在550℃获得良好的表面形貌,并应用于高质量SiGe材料的二次外延,解决了SiGe弛豫衬底二次外延中表面处理这一难题。（5）创新性地提出了基于SiGe虚衬底的SiGe HPT,对器件特性进行了系统的模拟分析,并在氧化法和低温Ge缓冲层法制备的SiGe弛豫衬底上完成了这种新型器件的制备。SiGe HPT的击穿电压BV_CEO达到14V,暗电流密度在-5V偏压时为4mA/cm²。在1.55μm波长处SiGe HPT的响应度为1.94mA/W,实现了以量子阱作为吸收区的SiGe HPT在1.55μm波长的响应,比目前报道的SiGe HPT在相同的入射方式下获得的最高响应度提高了20倍。更多还原

【Abstract】 The communication market has experienced a substantial and rapid growth over the past few years, which will require higher speed and low cost semiconductor devices in the future communication units. One of the solutions to meet these requirements is the concept of a complete communication system integrating electron devices and optoelectronic devices on a single chip. The successful development of high-speed SiGe heterojunction bipolar transistor （HBT） has provided the opportunity to integrate RF/microwave circuits and CMOS low-power circuit on a single chip in the wireless communication units. At the same time, SiGe heteroj unction bipolar phototransistor （HPT） with high external quantum efficiency, low noise and compatibility of the device’s epitaxial structure and fabrication with that of the HBT becomes more attractive for high-speed optoelectronic integrated circuit applications. However, it is a great challenge to obtain higher responsivity in near-infrared communication band for the traditional SiGe HPT due to the lower Ge content and the limitation of the critical thickness of SiGe layer on Si substrates. In this thesis, in order to improve the responsivity and extend the detection wavelength of SiGe HPT as well as the power and frequency of SiGe HBT, comprehensive theoretical designs and systemic experiments on SiGe HBT and HPT have been carried out. The main works and results are summarized as follows:（1） A homemade double-chamber chemical vapor deposition system was built and tested. Based on the growth kinetics of SiGe alloy, the growth conditions including source gas flux and substrate temperature were optimized for reaching certain Ge contents, growth rates and doping concentrations of SiGe layer, which pave the way for the following study of SiGe HBT and HPT.（2） A microwave power SiGe HBT with cut-off frequency of 2GHz have been designed and fabricated. We found that a little increase of Ge content in SiGe base region such as from 0.20 to 0.23 could lead to significant increase in current gain from 60 to 158. It was observed that the SiGe HBTs present positive and negative thermal-electric feed back when the base was biased with voltage and current source respectively. Those opposite trends of thermal-electric feed back were successfully utilized to compensate the self-heating effect of SiGe HBT by inserting a certain ballast resistance in the bias circuit.（3） High quality SiGe relaxed substrate based on Si and SOI substrate were prepared by dry oxidation. With lots of oxidation data, a SiGe oxidation kinetic model including the stress in the oxide was proposed for the first time. We found that the growth rate enhancement in SiGe oxidation process was induced by the lower activation energy of oxygen diffusivity rather than the weaker Ge-Ge bond energy reported by other group. More important, the self-limiting oxidation of SiGe alloy, which was still under debate, can be better understood in this model.（4） Thermal cleaning of SiGe surface under ultra-high vacuum has been systematically investigated. We found that Ge islands preferentially formed in the process of decomposition of native oxide covering the SiGe layer. The size and density of Ge islands could be controlled by the initial Ge content of the SiGe layer, which offered a simple route to fabricated small Ge quantun dots. However, for the SiGe layer passivated with hydrogen, lots of pits formed in the SiGe film during vacuum thermal annealing. When the temperature decreased to 550℃, a planar surface of SiGe substrate was obtained, on which a high quality SiGe epitaxy layer with the same content was also successfully achieved.（5） A novel SiGe HPT based on SiGe virtual substrate has been proposed and fabricated for the first time. The SiGe HPT showed a break voltage BV_ceo of about 14V and a low dark current density in the order of 4mA/cm² at 5V. The responsivity of 1.94mA/W was achieved at 1.55μm for normal incidence, which was about 20 times higher than that of previous SiGe HPT with Ge dot absorption layer reported by other group. It was also the first time to extent the response wavelength up to 1.55μm for SiGe HPT with multi-quantum-well absorption region.更多还原