Magnetotransport Properties Of AlGaN/GaN Heterostructure And HgTe Single Crystal

With the continuous improvement of the integration of micro-nano electronic devices,the semiconductor process is constantly approaching the atomic scale,and the quantum effect on the performance of the device makes the use of new technical paths to get rid of this dilemma become an urgent research topic.The study of spintronics and topological materials is a hot topic in this research topic.Based on this background,this paper mainly studies the low temperature magnetic transport phenomenon of AlGaN/GaN heterojunction and HgTe single crystal:（1）The basic transport properties of two Al_xGa_1-xN/GaN（x=0.087,0.33）heterojunction samples were studied:electron concentration and mobility were obtained through Sd H oscillation and quantum Hall effect.By fitting Sd H oscillation at different temperature,the effective mass of electrons was obtained.Fast Fourier transform showed that both samples were occupied by single subband.Fitting the weak antilocalization effects of both samples,the temperature dependence of the decoherence time was obtained.（2）The slow relaxation and anomalous field effects in Al_xGa_1-xN/GaN（x=0.087）heterojunction under gate voltage manipulation were studied.A significant electrical hysteresis at low temperature and an abnormal decrease of the resistance of the negative gate voltage region were observed.Through the Hall effect analysis under low magnetic field,the electrical hysteresis was found to originate from the electron transfer,driven by the electric field,between the two-dimensional electron gas conduction channel and the localized defect energy level outside the channel.The abnormal reduction of the resistance in the negative gate region is affected by the scattering mechanism.Through derivation,a negative correlation between mobility and carrier concentration is obtained.The higher the concentration,the lower the mobility,indicating that the main scattering mechanism in the sample at low temperature is interface roughness scattering.（3）The negative magnetoresistance effect of HgTe single crystal when the current is parallel to the direction of the magnetic field is studied.The square and strip samples were prepared separately,and the Van der Pauw method and the four-electrode method were used for measurement.For square samples,the measurement results show a strong negative magnetoresistance effect.Through analysis,the negative reluctance should be mainly caused by uneven current distribution.The measurement results of the four-electrode method show that the influence of the uneven current distribution in the sample is significantly suppressed,and the negative magnetic resistance should mainly come from the chiral anomaly effect.However,because the carrier concentration in the sample is too high,the Fermi level deviates much from the Weyl points,and the magnitude of the negative magnetoresistance effect change is not large enough.