碳化硅宽带隙半导体材料生长技术及应用
日期:2007-4-29王强,李玉国,石礼伟,孙海波 |
(山东师范大学半导体研究所,山东 济南 250014) |
摘要:概括了宽带隙半导体材料碳化硅的主要特性及生长方法,介绍了其在微电子及光电子领域的应用,并对其发展动态及存在问题进行了简要评述。 关键词:宽带隙半导体;碳化硅;光电子学 1 introduction as it is well known,the traditional si and gaas devices are inapplicable at the temperature above 250 ℃,and they cannot perform well under the conditions of high frequency,high power and strong radiation. when compared with si and gaas,sic material has many advantages,such as wide bandgap,high breakdown field,high thermal conductivity,high saturated drift velocity of electrons,stable chemical properties and survival ability in strong radiation,which make it a promising candidate in the adverse circumstance where the silicon devices have been disabled. taking the advantage of its wide bandgap(23 ev~33 ev),the blue,green and ultraviolet lightemitting devices and photo detectors have been fabricated. what is more,a naturally formed thin layer of sio2 on its surface is advantageous to the devices based on sic mos,which is unique,when compared with other compounds such as gan and aln,etc. nowadays the studies of sic are mainly focused on the crystalline growth and the formation of thin films of 4hsic,6hsic,3csic,and the investigation of sic devices have also gained much concern in recent years. in this article,the progresses of sic are discussed,and the existing problems are appraised and commented. 2the basicproperties semiconductor properties width=276> |
2.2 poly types width=240>
3 the prearation crystal
a majority of semiconductor crystals can be prepared in their melted state or in solution. but sic cannot be melted under traditional condition,and it cannot be prepared in any solutions until now. the acheson method is the earliest method to form sic crystal. in the year of 1955,lely used the sublimation method(without seed crystal)to form 3csic with pin shape. from the late 70 s to the early 80 s of last century,tairov and tsvetkov improved the lely method,and realized the seeded sublimation of sic.
3.1.1sic prepared by acheson method
for a long time,the growth of sic bulk crystal had been the bottleneck of the application of sic in the field of electronics. in the early years,people used the acheson method to form sic(fig.3). silica and carbon were mixed and reacted at the temperature above 2500 ℃,so someone said that,“silicon carbide is born in fire”. the carborundum(sic)formed by acheson method is mainly used as materials for abrasion and cutting,but it can also be used as electronic material for rather low requirement. due to such disadvantages as high growth temperature and poor crystal quality,it is being replaced by subsequent techniques such as lely method,modified lely method and cvd epitaxy method.
3.1.2 sic prepared by the lely method and the modified lely method
the crystal sic formed by lely method(fig.4)has greatly improved crystal quality,but its growth rate is rather low,and the type of the crystal cannot be controlled. nowadays sic formed by this method is usually used as substrate to obtain high quality epitaxial crystal. from the 80 s of last century,the sublimation method(modified lely method(fig.5)),which is also called physical vapor transport method(pvt),has been employed to grow sic crystal,and it has been the predominant method for sic production. but the growth temperature is still high(above 2100 ℃),large amount of micropipes and high density of dislocations exist in the crystal. and the control of the type of the crystal is difficult. until the 90 s of the last century,the fabrication technique had been greatly improved,and the 4hsic and 6hsic wafers with low density of micropipe defects(10~100 micropipes/cm2)had been obtained. the doping of sic is often in the process of its growth,and the ntype sic is doped by nitrogen,while the ptype is doped by aluminum. the doping after growth is often realized by the ion implantation technology,and the common diffusion method cannot get high doping concentration. due to the nitrogen gas ambience in the growth process,the unintentionally doped sic is of n type. nowadays there are four companies who can provide commercialized sic wafers,that is,cree research inc.(usa),nippon steel(japan),at mi corp.(usa),sicrystal ag(germany),and the sic wafers are mostly prepared by the sublimation method.
3.2 the growth width=243>