锗氮共掺碳化硅晶体杂质浓度表征及其电学性质研究

Characterization and Electrical Property of Impurity Concentration in Ge-N Codoped SiC Crystals

采用物理气相传输(PVT)法生长了2英寸(1英寸=25.4 mm)锗氮(Ge-N)共掺和单一Ge掺杂碳化硅晶体材料,并制备成10 mm′10 mm的SiC晶片。利用半导体工艺技术在不同衬底的碳面上制备钛(Ti)/铂(Pt)/金(Au)多层金属电极。使用二次离子质谱仪(SIMS)、霍尔测试仪(Hall)等测试手段对其表征。结果表明,Ge元素和N元素的共同掺杂可以有效提高SiC中Ge元素的掺杂浓度,Ge浓度可以达到1.19′1019/cm3。所有晶片衬底均可以在不低于700℃的退火环境中形成欧姆接触,且在700℃时退火形成最佳欧姆接触。高浓度Ge掺杂衬底接触电阻明显小于低浓度Ge掺杂衬底接触电阻,这表明可以通过提高晶体中Ge元素浓度来提高器件性能。Hall测试结果表明,随着Ge掺杂浓度的升高,衬底迁移率会逐渐降低。这是由于Ge-N共掺后,SiC晶格匹配度提高,Ge元素的掺杂浓度变大,增加了杂质散射对迁移率的影响。

2-inch Ge-N codoped and Ge doped SiC single crystals were grown by physical vapor transport（PVT） method.And the SiC ingots were fabricated into 10 mm′10 mm SiC wafers for characterization.Semiconductor technology was used to fabricate Ti/Pt/Au metal contact on the carbide-terminated face of SiC wafers.Subsequently,all samples were characterized by secondary ion mass spectrometry（SIMS） and Hall measurements.The SIMS results showed that Ge-N codoping method could enhance the Ge doping concentration in SiC crystals effectively,which could achieve 1.19′1019/cm-3.According to Hall measurement,ohmic contact could be obtained when samples were annealed at temperature higher than 700℃ and the optimal annealing temperature was 700℃.In addition,the contact resistance of the heavy Ge doped sample was lower than that of the light doped one,indicating that the ohmic contact property could be enhanced by improving the Ge doping concentrations in SiC crystals.Furthermore,as the increase of Ge doping concentration,the mobility gradually decreased.It was ascribed to that the Ge-N atoms matched well with SiC lattice in codoping method leading to higher Ge doping concentration.Under that condition,the impurity scattering effect became evident,which resulted in a lower mobility for Ge-N codoped sample.