半导体异质结二维电子气的磁输运特性研究
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摘要
半导体异质结二维电子气的磁阻振荡是由电子的量子效应引起的,反映朗道能级态密度在费米面处的变化。通过磁输运(Transport)测量来研究二维电子气的磁阻振荡,可以获得丰富的材料电学特性以及电子子带性质。本文主要通过深低温,强磁场下的Shubnikov-de Haas(SdH)效应测量和常规变磁场霍尔测量,采用快速Fourier变换方法(FFT),并结合定量迁移率谱(QMSA)和多载流子拟合(MCF),系统地研究了不同材料异质结二维电子气的磁阻振荡,并得到以下具有创新性的研究结果:
1.观察到在AlGaN/GaN异质结界面处的二维电子气占据两个子带,以及由电子子带间散射引起的磁阻振荡,该振荡不同于SdH振荡,它对温度的变化不敏感,也不依赖于费米能级,只与两个子带的能级间距有关。并在一定温度范围内观察到磁阻拍频现象,其来源于该磁阻振荡与SdH振荡的相互叠加。根据Sander等人和Raikh等人给出的磁阻振荡的具体表达式,拟合实验结果表明磁阻拍频是由第一子带SdH振荡和磁致子带间散射引起的磁阻振荡导致的。
2.观察到AlGaN/GaN异质结二维电子气的磁阻振荡在低场下出现正,负磁阻变化,分析表明其来源于AlGaN/GaN异质结二维电子气中的量子相干散射,表现为电子的反弱局域化与弱局域化效应。根据Hikami,Larkin和Nagaoka给出的扩散近似下的磁导率随磁场变化关系式,拟合实验结果得到电子自旋-轨道散射时间以及非弹性散射时间。电子的自旋-轨道散射主要来源于晶体场引起的自旋分裂,不受晶格温度的影响,而非弹性散射时间与温度成反比关系,表明非弹性散射机制主要来源于小能量转移的电子-电子散射。
3.通过对调制掺杂的n型Hg_(0.82)Cd_(0.16)Mn_(0.02)Te/Hg_(0.3)Cd_(0.7)Te第一类量子阱中磁性二维电子气磁阻拍频振荡的研究,发现温度,栅压的变化都会引起磁阻拍频节点位置的变化。从对拍频的分析中,可以将依赖于栅压的Rashba自旋-轨道分裂和依赖于温度的巨大塞曼分裂区分开来。
The magnetoresistance oscillations of semiconductor heterojunction two-dimensional electron gas(2DEG) originate from electron quantum effect, which reflecting the state density variation of Landau energy at Fermi level. We can study the magnetoresistance oscillations of two-dimensional electron gas by magnetotransport measurement, by which we can get abundant electrical character and electrons-subband property. We systematically investigate magnetoresistance oscillations of heterojunction two-dimensional electron gas for different material by Shubnikov-de Haas(SdH) effect measurement and normal vary magnetic-field Hall measurement under very low temperature and high magnetic-field, and adopt fast Fourier transform, as well as combine quantitative mobility spectrum analysis and multi-carrier fit, then obtain the following results:1. The magnetoresistance oscillations caused by electron intersubband scattering, as well as the two subbands occupied by two-dimensional gas in AlGaN/GaN heterojunction interface have been observed, which is independent of the temperature, difference from SdH oscillation. And striking beating patterns in magneto-resistance vs magnetic field are observed in the vicinity of a special temperature. Theoretical simulation is performed and the comparison between numerical simulations and the experimental data reveals that the beating patterns are due to the interference of the magneto-intersubband scattering and the SdH oscillator of first subband.2. The magnetoresistance oscillations of AlGaN/GaN heterojunction two-dimensional gas represent the vary of first positive and then negative, analysis
indicate that which is coming from quantum coherent scattering in AlGaN/GaN heterojunction two-dimensional gas and express as electrons weak anti-localization and localization effect. According to the theory given by Hikami, Larkin and Nagaoka that relation of magnetic conductivity with the varying of magnetic field under diffusion approximation, we fitting results of experiments and get spin-orbit scattering time and inelastic scattering times. Spin-orbit scattering of electrons is mainly coming from spin-splitting induced by crystal-field, which is independent from the lattice temperature, while the inelastic scattering time is found to follow the inverse relation with temperature, which indicate that electron-electron scattering with small energy transfer is the dominant inelastic process.3. We detailed study the beating oscillation in Shubnikov-de Hass (SdH) of magnetic two dimensional electron gas consisting of a modulation doped n type Hg0.82Cd0.16Mn0.02Te/Hg0.3Cd0.7Te first type quantum well, by which found that temperature, gate voltage are both bring the variety of magnetic resistance beating node position. By analyzing beating patterns, gate voltage dependent Rashba spin-orbit splitting can be separated from temperature dependent giant Zeeman splitting.4. Shubnikov-de Haas(SdH) effect and the Hall effect of the In0.53Ga0.47As/In.52Al0.48As single quantum well with two subbands occupation have been studied, and have obtained the electron concentration, mobility, effective mass and energy levels respectively. The concentration of the two subbands deduced by Mobility Spectrum and Multi-Carrier Fitting(MS+MCF) is well consistent with the result from the SdH oscillation. It is observed that there is a frequency of f1-f2 insensitive to the temperature, as well as the frequencies of f1, f2 for the two subbands
and the frequency doubling 2fi dependent of the temperature from Fast Fourier Transform(FFT) for d2 P /dB2—1/B, it is because that the electrons have the same effective mass in different subbands and then the magneto-intersubband scattering between the two subbands has taken place strongly.
1.观察到在AlGaN/GaN异质结界面处的二维电子气占据两个子带,以及由电子子带间散射引起的磁阻振荡,该振荡不同于SdH振荡,它对温度的变化不敏感,也不依赖于费米能级,只与两个子带的能级间距有关。并在一定温度范围内观察到磁阻拍频现象,其来源于该磁阻振荡与SdH振荡的相互叠加。根据Sander等人和Raikh等人给出的磁阻振荡的具体表达式,拟合实验结果表明磁阻拍频是由第一子带SdH振荡和磁致子带间散射引起的磁阻振荡导致的。
2.观察到AlGaN/GaN异质结二维电子气的磁阻振荡在低场下出现正,负磁阻变化,分析表明其来源于AlGaN/GaN异质结二维电子气中的量子相干散射,表现为电子的反弱局域化与弱局域化效应。根据Hikami,Larkin和Nagaoka给出的扩散近似下的磁导率随磁场变化关系式,拟合实验结果得到电子自旋-轨道散射时间以及非弹性散射时间。电子的自旋-轨道散射主要来源于晶体场引起的自旋分裂,不受晶格温度的影响,而非弹性散射时间与温度成反比关系,表明非弹性散射机制主要来源于小能量转移的电子-电子散射。
3.通过对调制掺杂的n型Hg_(0.82)Cd_(0.16)Mn_(0.02)Te/Hg_(0.3)Cd_(0.7)Te第一类量子阱中磁性二维电子气磁阻拍频振荡的研究,发现温度,栅压的变化都会引起磁阻拍频节点位置的变化。从对拍频的分析中,可以将依赖于栅压的Rashba自旋-轨道分裂和依赖于温度的巨大塞曼分裂区分开来。
The magnetoresistance oscillations of semiconductor heterojunction two-dimensional electron gas(2DEG) originate from electron quantum effect, which reflecting the state density variation of Landau energy at Fermi level. We can study the magnetoresistance oscillations of two-dimensional electron gas by magnetotransport measurement, by which we can get abundant electrical character and electrons-subband property. We systematically investigate magnetoresistance oscillations of heterojunction two-dimensional electron gas for different material by Shubnikov-de Haas(SdH) effect measurement and normal vary magnetic-field Hall measurement under very low temperature and high magnetic-field, and adopt fast Fourier transform, as well as combine quantitative mobility spectrum analysis and multi-carrier fit, then obtain the following results:1. The magnetoresistance oscillations caused by electron intersubband scattering, as well as the two subbands occupied by two-dimensional gas in AlGaN/GaN heterojunction interface have been observed, which is independent of the temperature, difference from SdH oscillation. And striking beating patterns in magneto-resistance vs magnetic field are observed in the vicinity of a special temperature. Theoretical simulation is performed and the comparison between numerical simulations and the experimental data reveals that the beating patterns are due to the interference of the magneto-intersubband scattering and the SdH oscillator of first subband.2. The magnetoresistance oscillations of AlGaN/GaN heterojunction two-dimensional gas represent the vary of first positive and then negative, analysis
indicate that which is coming from quantum coherent scattering in AlGaN/GaN heterojunction two-dimensional gas and express as electrons weak anti-localization and localization effect. According to the theory given by Hikami, Larkin and Nagaoka that relation of magnetic conductivity with the varying of magnetic field under diffusion approximation, we fitting results of experiments and get spin-orbit scattering time and inelastic scattering times. Spin-orbit scattering of electrons is mainly coming from spin-splitting induced by crystal-field, which is independent from the lattice temperature, while the inelastic scattering time is found to follow the inverse relation with temperature, which indicate that electron-electron scattering with small energy transfer is the dominant inelastic process.3. We detailed study the beating oscillation in Shubnikov-de Hass (SdH) of magnetic two dimensional electron gas consisting of a modulation doped n type Hg0.82Cd0.16Mn0.02Te/Hg0.3Cd0.7Te first type quantum well, by which found that temperature, gate voltage are both bring the variety of magnetic resistance beating node position. By analyzing beating patterns, gate voltage dependent Rashba spin-orbit splitting can be separated from temperature dependent giant Zeeman splitting.4. Shubnikov-de Haas(SdH) effect and the Hall effect of the In0.53Ga0.47As/In.52Al0.48As single quantum well with two subbands occupation have been studied, and have obtained the electron concentration, mobility, effective mass and energy levels respectively. The concentration of the two subbands deduced by Mobility Spectrum and Multi-Carrier Fitting(MS+MCF) is well consistent with the result from the SdH oscillation. It is observed that there is a frequency of f1-f2 insensitive to the temperature, as well as the frequencies of f1, f2 for the two subbands
and the frequency doubling 2fi dependent of the temperature from Fast Fourier Transform(FFT) for d2 P /dB2—1/B, it is because that the electrons have the same effective mass in different subbands and then the magneto-intersubband scattering between the two subbands has taken place strongly.
引文
[1] E. H. Putley, The Hall Effect (London:Butterworth, 1960)
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[4] R. A. Reynolds, M. J. Brau, H. Kraus, and R. T. bate, J. Phys. Chem. Solids 32, 511 (1971)
[5] M. C. Gold and D. A. Nelson, J. Vac. Sci. Technol. A4, 2040 (1986)
[6] W. A. Beck and J. R. Anderson, J. Appl. Phys. 62, 541 (1987)
[7] D. L. Leslie-Pelecky, C. L. Littler, Appl. Phys. Lett. 23, 1916 (1987)
[8] J. R. Meyer et al, Semicond. Sci. Technol, 8, 805 (1993)
[9] E. F. Schubert et al, IEEE Trans. Electron Device, ED-33, 625 (1986)
[10] N. W. Ahcroft et al, SolidState Physics (New York, 1976) p. 554
[2] L. J. van der Pauw, Philips. Tech. Rev. 20, 220 (1958)
[3] D. D. Edwall, E. R. Gertner, and W. E. Tennant, J. Electron. Mater. 14 245 (1985)
[4] R. A. Reynolds, M. J. Brau, H. Kraus, and R. T. bate, J. Phys. Chem. Solids 32, 511 (1971)
[5] M. C. Gold and D. A. Nelson, J. Vac. Sci. Technol. A4, 2040 (1986)
[6] W. A. Beck and J. R. Anderson, J. Appl. Phys. 62, 541 (1987)
[7] D. L. Leslie-Pelecky, C. L. Littler, Appl. Phys. Lett. 23, 1916 (1987)
[8] J. R. Meyer et al, Semicond. Sci. Technol, 8, 805 (1993)
[9] E. F. Schubert et al, IEEE Trans. Electron Device, ED-33, 625 (1986)
[10] N. W. Ahcroft et al, SolidState Physics (New York, 1976) p. 554
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