Study Of Transport And Magnetic Properties On Doped InN Films

Semiconductor based devices have a very intimacy relationship with the physical properties of semiconductor itself.Recently,great attentions have been paid on the Ⅲ-Ⅴ semiconductor,among which,indium nitride(InN)is the one with the lowest effective electron mass.According to the classic knowledge of semiconductor,low effective mass means high mobility and saturation velocity.All those amazing properties are very attractive in applications like transistors,light emitting diodes and solar cell.With the development of epitaxy technique,high quality InN film is accessible,which shows much lower band gap,～0.6 eV,compared with previously reported 2 eV.The new band gap parameter again brings InN back into people’s attention for several reasons.First,the In1-xGaxN alloy can cover the whole sun spectrum from infrared to ultraviolet through changing the stoichiometry of Ga atoms,which makes it very potential in light emitting diodes.Another thing is,the small band gap coincides with the wavelength used in optical fiber(1310nm or 1550nm)so that high quality InN or alloys might be applicable in high speed telecommunication.However,since N vacancy is unavoidable during the growth,the as grown InN always exhibit n-type conductivity.P type conductivity is difficult to achieve because the stabilized Fermi level is pinned in conduction band,which block the way to further technological application.This thesis focuses on the p-type conductivity and other physical properties of high quality InN film.Based on our first principle calculation,we tried to induce acceptor defects or intrinsic defects through implanting Mg,Ba,Zn and Mn ions or changing the growth condition.Following well studied InN:Mg,p-type conductivity is achieved in InN:Ba and InN:Zn films,providing other choices for devices.Besides,coexistence of superconductivity and ferromagnetism is discovered in InN films with dophant or In vacancy.We also studied the persistent reconstruction on SrRuO3(111)surface,which should be taken into consideration for further study on heterostructures.Following are the main results of our researches:1)Achievement of p-type conductivity in InN:Ba and InN:Zn films.There are three valence electrons in indium atom,so doping atoms with two valence electrons on In site of InN can create acceptor defects,inducing acceptor energy level in band gap and resulting in system with holes as the dominant carrier.However,severe self-compensation of carriers makes it an international conundrum to realize p-type conduction in InN films.Employing first principle calculation,we calculated the formation energy of the acceptor defects for all the possible dopants,turning out that Mg,Sr,Zn,Mn and Ba might be potential.To realize unbalanced doping process,ion implantation is used to introduce Zn and Ba into InN films.For InN:Ba,the PL signal gets weaker with the increasing of Ba density,suggesting the existence of hole in bulk which form an electrical potential with the surface electron accumulation layer.This coexistence of both hole and electron is also supported by the kink in the curve of Hall mobility versus temperature.For InN:Zn,we got positive Hall coefficient at low temperature,which is a direct evidence for hole conduction.Hall coefficient changes its sign to negative when the temperature gets high enough because high temperature excites more intrinsic donor type defects and makes electron as the dominant carrier.2)Studies on the coexistence of superconductivity and ferromagnetism in InN systems.InN and InN:Zn films exhibit a normal-superconducting state transition at round 3.8 K,which might origin from the interaction between nearest In atoms in ab plane.Compared with InN films,the pinning effect from Zn implantation makes InN:Zn system more robust to magnetic field.The fitting of activation versus magnetic field further support the two dimensionality of superconducting source.When measuring the hysteresis loop,we found the coexistence of signal from both superconductivity and ferromagnetism.Since the electrons on N p orbital near ZnIn defects are not fully paired,spin polarization happens based on Hund’s rule.Coupling between those local moment leads to long distance magnetic ordering.Furthermore,we studied the InN/Al2O3 system,in which In vacancies are formed because of the large lattice mismatch.It is proved both experimentally and theoretically that In vacancy results in ferromagnetism in InN/Al2O3 film.3)Studies on a,((?))R300 surface reconstruction in SrRuO3(SRO)(111)films.SrRuO3 is an itinerant ferromagnetic perovskite oxide,whose magnetic and electric properties are correlated with film thickness,growth quality and orientation.The enhancement of magnetism in SRO(111)films attracts lots of attentions.We found the SRO(111)films exhibit a persistent((?))R30° surface reconstruction.Such reconstruction is not due to the orthorhombic distortion existing in the bulk SRO.Instead,it is the formation of the ordered oxygen vacancies to minimize the surface energy and compensate the surface polarity.In-situ post annealing with oxygen diminishes such vacancy ordering and enhances the surface metallicity.We expect that a better understanding of the SRO(111)surface and the ability to control the surface structure will pave the way for realizing new multifunctional heterostructures.