Study On Magnetotransport Properties Of Superconducting InN

As the only material with superconducting properties in III-V semiconductors,InN is the foundation for the III-V semiconductor based superconductor/semiconductor integration.However,due to the phase-separated superconducting In/In₂O₃ inclusions in InN,the intrinsic superconductivity of InN has been questioned for many years.Three key issues concerning InN's superconductivity were discussed in this thesis:1.To study the intrinsic superconductivity of InN,the chemical-unstable phase-separated In/In₂O₃ inclusions are intentionally removed by HCL acid etching.The quasi-two-dimensional vortex liquid-glass transition is observed in the sample with a large InN grain size.In contrast,the superconducting properties of InN with a small grain size are sensitive to acid etching,showing a transition into a nonzero resistance state when the temperature approaches zero.It is suggested that intergrain coupling should be responsible for the sample-dependent InN superconducting phase transition.Also,a differential resistance peak is observed near the critical current in d V/d I vs I curve of InN.The evolution of peak position under temperature and magnetic field shows a nice quantitative agreement with the intrinsic Josephson junction model2.To study the flux pinning properties of InN superconductor,the I-V relationships,R-B transitions,and R-T transitions are investigated.A complete flux phase diagram is provided based on the results of I-V scaling.The R-T curves are well fitted by thermally activated flux flow?TAFF?model.The TAFF activated energy satisfies a power-law relationship with magnetic field,but it has two different exponents under the low magnetic field and high magnetic field.We explain it as the result of a transition from single flux pinning to collective flux pinning which also leads to the rapid attenuation of critical current as the magnetic field increases.By analyzing the temperature dependence of critical current,we found the dominant?L-pinning mechanism.Furthermore,the dependence of pinning force on magnetic field is analyzed using the Dew-Hughes model,and the results show that the main pinning center is the point pinning.3.The optical response characteristics of InN in the superconducting state were studied for the first time.Compared with the photoresponse of the semiconductor state,InN has an ultrasensitive photoresponse in the superconducting state,with a photo-induced resistivity change approximately 200 times greater than in the semiconductor state.Taking advantage of the sharp phase transition of superconductivity in critical state,a dramatic enhancement of sensitivity is obtained with a maximum responsivity up to 4.76 10 V/W and a noise-equivalent power?NEP?of ???.The response mechanism is attributed to the superconducting bolometric effect.Our work paves the way for studying InN's superconducting single photon detectors.