Multisubband transport of the two-dimensional electron gas in AlxGa1−xN/GaN heterostructures
Zhongming ZhengBo ShenChunping JiangY. S. GuiTakao SomeyaR. ZhangYanmeng ShiY. D. ZhengS. L. GuoJunhao ChuYasuhiko Arakawa
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Multisubband transport of the two-dimensional electron gas (2DEG) in modulation-doped Al0.22Ga0.78N/GaN heterostructures has been investigated by means of magnetotransport measurements at low temperatures and high magnetic fields. It is found that the mobility of the 2DEG in the first subband in a triangular quantum well at the heterointerface decreases significantly, while the mobility of the 2DEG in the second subband increases, when the Al0.22Ga0.78N barrier is partially relaxed. Such behavior of the 2DEG mobility is explained by the nonuniformity of the piezoelectric polarization field at the heterointerface induced by the Al0.22Ga0.78N relaxation and strong interface scattering. Meanwhile, it is concluded that the scattering from the remote ionized donors is the main mechanism contributing to the quantum scattering time and responsible for the intersubband scattering in the quantum well at the heterointerface.Keywords:
Shubnikov–de Haas effect
Electron Mobility
In order to characterize the electron transport properties of the two-dimensional electron gas (2DEG) in AlGaN/GaN modulation-doped field-effect transistors, channel magnetoresistance has been measured in the magnetic field range of 0–12 T, the temperature range of 25–300 K, and gate bias range of +0.5 to −2.0 V. By assuming that the 2DEG provides the dominant contribution to the total conductivity, a one-carrier fitting procedure has been applied to extract the electron mobility and carrier sheet density at each particular value of temperature and gate bias. Consequently, the electron mobility versus 2DEG sheet density has been obtained for each measurement temperature. Theoretical analysis of these results suggests that for 2DEG densities below 7×1012 cm−2, the electron mobility in these devices is limited by interface charge, whereas for densities above this level, electron mobility is dominated by scattering associated with the AlGaN/GaN interface roughness.
Electron Mobility
Wide-bandgap semiconductor
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Magnetotransport properties of modulation-doped Al/sub x/Ga/sub 1-x/N/GaN heterostructures were studied at low temperatures and high magnetic fields. The strong Shubnikov-de Hass oscillations with the double periodicity is clearly observed, indicating the two-dimensional electron gas (2DEG) occupation of the double subbands in the triangular quantum well at the heterointerfaces. It is determined that the 2DEG occupation of the double subbands occurs when the 2DEG sheet concentration reaches 9.0 /spl times/ 10/sup 12/cm/sup -2/, and the energy separation between the first and the second subbands is 75 meV. The quantum scattering time related to the first subband is determined to be 8.4 /spl times/ 10/sup -14/ s. The mobilities of the 2DEG in the first and the second subbands, magnetointersubband scattering oscillations of the 2DEG and the spin splitting of the 2DEG have also been studied.
Shubnikov–de Haas effect
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Classical transport and magnetotransport of the two-dimensional electron gas (2DEG) in modulation-doped Al/sub x/Ga/sub 1-x/N/GaN heterostructures have been investigated. In magnetotransport measurements at low temperatures and high magnetic fields, strong Shubnikov-de Hass (SdH) oscillations with double periodicity are clearly observed, indicating the 2DEG occupation of the double subbands in the triangular quantum well at the heterointerfaces. Based on the observation of the SdH oscillation with double periodicity, the sheet concentrations and the mobilities of the 2DEG in the first and the second subbands, magneto-intersubband scattering (MIS) oscillations of the 2DEG, and the spin splitting of the 2DEG in the quantum well at the heterointerfaces are studied and discussed.
Shubnikov–de Haas effect
Oscillation (cell signaling)
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The line shape of the Shubnikov-de Haas (SdH) oscillation has been analyzed in detail for a GaAs/AlGaAs two-dimensional electron gas. The line shape, or equivalently the behavior of the Fourier components, of the experimentally observed SdH oscillation is well reproduced by the sinusoidal density of states at the Fermi energy that oscillates with a magnetic field in a saw-tooth shape to keep the electron density constant. This suggests that the broadening of each Landau level by disorder is better described by a Gaussian than by a Lorentzian.
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Shubnikov–de Haas effect
Line (geometry)
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Landau quantization
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We have performed high field magnetotransport measurements to investigate the interface electron gas in LaAlO3/SrTiO3 heterostructures. Shubnikov-de Haas oscillations reveal several 2D conduction subbands with carrier effective masses between 1 and 3 m_e, quantum mobilities of order 3000 cm^2/V s, and band edges only a few millielectronvolts below the Fermi energy. Measurements in tilted magnetic fields confirm the 2D character of the electron gas, and show evidence of inter-subband scattering.
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Fermi energy
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We calculate the electron mobility limited by the AlxGa1−xN barrier and the GaN well thickness fluctuations scattering of the two-dimensional electron gas (2DEG) at AlxGa1−xN/GaN multi-quantum wells (MQWs) with a triangle potential well. For this potential well, the ground subband energy is governed by the spontaneous and piezoelectric polarization fields and the fields are determined by the barrier and well thicknesses in undoped AlxGa1−xN/GaN MQWs. Thus, the thickness fluctuations of AlxGa1−xN barrier and GaN well will cause a local fluctuation of the ground subband energy, which will reduce the 2DEG mobility.
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Rectangular potential barrier
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A series of GaAs/InGaAs quantum wells with a silicon δ-doped layer in the top barrier was investigated by Shubnikov–de Haas measurements as a function of the illumination time of the samples. During the illumination process strong modifications of the electronic density and the quantum mobility of each occupied subband were observed. Based on self-consistent calculations, the dominant mechanism which caused the changes in the subband quantum mobilities with illumination was elucidated.
Shubnikov–de Haas effect
Electron Mobility
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Magnetotransport properties of modulation-doped Al0.22Ga0.78N/GaN heterostructures were investigated by means of magnetoresistance measurements at low temperatures and high magnetic fields. Strong Shubnikov–de Haas oscillations with the double periodicity are observed. The mobility spectrum is obtained, which demonstrates that the mobilities of the two-dimensional electron gas (2DEG) in the two subbands in the triangular quantum well at heterointerface. It is found that the mobility of the 2DEG in the second subband is much higher than that in the first one. This is explained that interface roughness scattering and alloy disorder scattering have much stronger influence on transport properties of the 2DEG in the first subband than that in the second subband in AlxGa1−xN/GaN heterostructures.
Shubnikov–de Haas effect
Electron Mobility
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Magnetotransport properties of the two-dimensional electron gas (2DEG) in Al/sub x/Ga/sub 1-x/N/GaN heterostructures have been investigated. We extrapolate that the second subband in the triangular quantum well at the heterointerface starts to be populated at a 2DEG concentration of about 7.23 /spl times/ 10/sup 12/ cm/sup -1/. The quantum scattering time related to the first subband is obtained as 0.144-0.146 ps for the heterostructures. Intersubband scattering is also observed in the heterostructures.
Characterization
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We have performed high field magnetotransport measurements to investigate the interface electron gas in a high mobility SrTiO3/SrCuO2/LaAlO3/SrTiO3 heterostructure. Shubnikov-de Haas oscillations reveal several 2D conduction subbands with carrier effective masses of 0.9me and 2me, quantum mobilities of order 2000 cm2/V s, and band edges only a few millielectronvolts below the Fermi energy. Measurements in tilted magnetic fields confirm the 2D character of the electron gas, and show evidence of inter-subband scattering.
Shubnikov–de Haas effect
Electron Mobility
Fermi energy
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