宽禁带半导体掺杂机制研究进展

Review of defect physics and doping control in wide-band-gap semiconductors

随着电子信息技术进入后摩尔时代,人们期望探寻一些新材料、新技术以推进半导体科学技术的发展.作为新一代战略电子材料,宽禁带半导体的技术应用近年来取得了飞速发展.宽禁带半导体的掺杂与缺陷调控是实现其重要应用价值的关键科学基础.本文主要介绍了我们和合作者近期围绕碳化物、氧化物、氮化物宽禁带半导体中掺杂与缺陷机理及性能调控展开的研究工作,具体包括:(1)探究4H-SiC中本征缺陷的电学和动力学性质,解释了实验上4H-SiC的有效氢钝化现象的内在物理机制;(2)研究In_(2)O_(3)中过渡金属元素的掺杂物理性质,提出了过渡金属掺杂的设计原则,并预测过渡金属Zr、Hf和Ta在In_(2)O_(3)中具有优异的n型特性;(3)采用轻合金化法调控Ga_(2)O_(3)材料的价带顶位置,并通过选取合适的受主杂质(如CuGa),有望使(Bi_(x)Ga_(1–x))_(2)O_(3)合金成为高效的p型掺杂宽禁带半导体;(4)研究Be和Mg在GaN中的缺陷行为,澄清Be掺杂比Mg掺杂具有更深受主能级的物理机制;(5)提出量子工程非平衡掺杂方法来调制AlGaN的价带,实现其高效p型掺杂;(6)探究缺陷掺杂行为随应力变化的普适性规律,并阐述如何通过压力调控在GaN中实现更高性能的p型掺杂.这些工作不仅加深了对宽禁带半导体材料的电子结构及掺杂与缺陷物理特性的理解,也对基于宽禁带半导体材料的器件设计与实际应用起到重要的指导和推进作用.

Wide-band-gap semiconductors are important materials for current and the post-Moore era technologies.Both basic research and technical applications of the wide-band-gap semiconductors have advanced rapidly in recent years.The wideband-gap semiconductors have already been widely applied in high temperature,radiation resistant,high frequency,high power,and high-density integrated electronics.However,the wide-band-gap semiconductors are known for their hard-todope properties.Thus,effective doping and defect control is the key to the applications of wide-band-gap semiconductors.In this paper,we review some recent work on doping properties of wide-band-gap carbide,oxide,and nitride semiconductors,which including:(1)The electrical and kinetic properties of the intrinsic defects in 4H-SiC and the underlying physical mechanism of the experimentally observed hydrogen passivation in 4H-SiC.The carbon vacancy VC is determined to be the main defect that affects the electrical properties of 4H-SiC.The configurations of the defect complex VC+nH(n=1–4)in 4H-SiC are identified,and VC+4H is found to be able to effectively passivate all the deep defect levels,which successfully explains the origin of the experimental phenomenon of hydrogen passivation.(2)The physical properties of transition metal doping in In_(2)O_(3)and the design principles of transition metal doping in TCOs.The dualdoping behavior of Mo in In_(2)O_(3)depending on the doping site is discovered,and it is expected that the transition metals Zr,Hf,and Ta can be the promising n-type dopants in In_(2)O_(3).(3)Strategies to achieve p-type doping in Ga_(2)O_(3)by raising its valence band maximum through alloying with Bi and by properly choosing doping impurities(e.g.,CuGa).Also the general approach to effectively doping wide-band-gap semiconductors with strongly correlated band edges is brought up.(4)The doping behaviors of Be and Mg in GaN,and clarifying the origin of why the acceptor level of Be is deeper than that of Mg in GaN.It is demonstrated that both the bigger size-mismatch induced structure relaxation and the covalency of the bonding between the Be and N atoms have contributed to the deeper BeGa acceptor.This has improved the understanding of nitrides doping with IIA elements,and provided theoretical guidance for more effective p-type doping in wide-band-gap nitrides.(5)A quantum mechanical modulation doping technique to achieve highly efficient p-type doping in AlGaN.A nonequilibrium doping method is proposed and implemented to modulate the valence band of AlGaN materials,the activation energy of Mg acceptor in AlGaN is reduced,and the p-type doping efficiency is greatly enhanced.(6)Studying the universal behavior and basic rules for the defect doping properties as a function of the applied strain,and designing how to achieve high efficient p-type doping in GaN through strain.It is proposed that the positive strain applied to GaN materials could reduce the ionization energy of MgGa to achieve higher performance of p-type doping.These pieces of work not only deepen our understanding on the electronic structure and doping properties in wide-band-gap semiconductors,but also play an important role in guiding and promoting the device designs and practical applications of wide-band-gap semiconductors.