Interface State Of Ge/SiC Heterojunction

Ge/SiC heterojunction is a possible solution for SiC devices from visible light to near-infrared light.The electrical and optical properties of the Ge/SiC heterojunction interface are different from bulk materials.Theoretically,the lattice mismatch between Ge and SiC is about 23.0%,and hence,the properties of Ge/SiC heterojunction are influenced by interface structure and microscopic characteristics to a large extent.Experimentally,research on Ge/SiC heterojunction has been carried out and important achievements have been obtained.However,little effort has been devoted to theoretical research on microscopic mechanism such as actual lattice matching,density of states,misfit dislocations density and bonding mechanism,etc.Therefore,in order to comprehensively investigate the issues related to the Ge/SiC heterojunction interface,the first-principles are employed to calculate bonding mechanism,preferential orientation and interfacial defects of Ge/4H-SiC hetero-interfaces.The main results are as follows:1.Adsorption of Ge atoms on the 4H-SiC(0001)surface,and the atomic electronic properties of the Ge(111)/4H-SiC(0001)hetero-interfaces and the Ge(110)/4H-SiC(0001)hetero-interfaces are analyzed using first-principles for the energy,electronic properties and density of states.2.Four Ge adsorption models on the 4H-SiC(0001)surface were established for top position,bridge position,hcp hole position,and fcc hole position.The results of adsorption energy indicate that the top position is the most stable adsorption position,and the geometric characteristics indicate that the smaller the bond length,the greater the adsorption energy.Population analysis and density of state show that Si-Ge bonds are formed between the Si atoms and the Ge-adsorbed atoms.3.Ge(111)/4H-SiC(0001)and Ge(110)/4H-SiC(0001)interface models are established.It is also shown that the work of adhesion of Ge(110)/4H-SiC(0001)interface is higher than that of the Ge(111)/4H-SiC(0001)interface,indicating the adhesive strength of Ge(110)/4HSiC(0001)hetero-interface is larger than Ge(111)/4H-SiC(0001)hetero-interface.By comparing the DOS of Ge(110)/4H-SiC(0001)and Ge(111)/4H-SiC(0001)hetero-interfaces,several distinct resonance peaks appear in the range of-4eV to 2eV.The peaks mainly originate from the orbital hybridization of Si-3p and Ge-4p,indicating the formation of Si-Ge bond at the interface.4.The relaxation energy of Ge(110)/4H-SiC(0001)interface is lower than that of Ge(111)/4H-SiC(0001)interface,suggesting that Ge(111)films are easier to deposit on 4HSiC(0001)substrates at relative high temperatures and Ge(110)films are easier to deposit on 4H-SiC(0001)substrates at relative low temperatures.However,when the Ge/SiC heterojunction grows,the coexistence of <111> and <110> modes often occurs,and the preferred growth of the <111> direction occurs more easily at high temperatures.5.The misfit dislocations density in domain matching(DM)mode is calculated.The results show that the misfit dislocations densities of Ge(110)/4H-SiC(0001)hetero-interface is smaller than that of Ge(111)/4H-SiC(0001)hetero-interface,which indicates that Ge(110)/4HSiC(0001)hetero-interface has fewer defects.