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Multisubband transport of the two-dimensional electron gas (2DEG) in modulation-doped Al[sub 0.22]Ga[sub 0.78]N/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 Al[sub 0.22]Ga[sub 0.78]N 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 Al[sub 0.22]Ga[sub 0.78]N 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. [ABSTRACT FROM AUTHOR]

Magnetointersubband scattering (MIS) oscillations of two-dimensional electron gas (2DEG) in Al[sub 0.22]Ga[sub 0.78]N/GaN heterostructures have been investigated by means of magnetotransport measurements at low temperatures and high magnetic fields. Double periodic Shubnikov–de Haas oscillations modulated by MIS oscillations have been observed due to the intersubband scattering of the 2DEG at the two lowest subbands in the triangular quantum well at the heterointerface. By using the fast Fourier transform analysis, it is found that the MIS oscillations become slightly weaker with an increase in temperature. From the MIS frequency, the energy separation between the first and the second subbands is determined to be 80 meV. The observation of the MIS effect indicates that the effective masses of the electrons in the first and second subbands are the same in Al[sub 0.22]Ga[sub 0.78]N/GaN heterostructures. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetotransport properties of modulation-doped Al[sub 0.22]Ga[sub 0.78]N/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 Al[sub x]Ga[sub 1-x]N/GaN heterostructures. [ABSTRACT FROM AUTHOR]

Influences of the thickness of the Si-doped n-type Al[sub 0.22]Ga[sub 0.78]N barrier and the thickness of the Al[sub 0.22]Ga[sub 0.78]N spacer on mobility and density of the two dimensional electron gas (2DEG) in modulation-doped Al[sub 0.22]Ga[sub 0.78]N/GaN heterostructures were investigated. 2DEG mobilities of 1274 cm2/V s at 300 K and 4495 cm2/V s at 77 K were reached. Both 2DEG mobility and density decrease dramatically when the Al[sub 0.22]Ga[sub 0.78]N barrier becomes partially relaxed, indicating that transport properties of the 2DEG are influenced significantly by the piezoelectric polarization of the Al[sub 0.22]Ga[sub 0.78]N layer. From our results, the critical thickness of an Al[sub 0.22]Ga[sub 0.78]N layer on GaN is estimated to be between 65 and 75 nm, which is much higher than that predicted by theoretical calculation. This may be attributed to the interaction of misfit dislocations and the presence of a high density of extended defects in the Al[sub 0.22]Ga[sub 0.78]N layer. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Transport properties of the two-dimensional electron gas (2DEG) in AlxGa1−xN/GaN heterostructures were investigated by means of magnetotransport measurements. The mobilities corresponding to the 2DEG in the first and the second subbands in the trianglar quantum well at the heterointerface were obtained. When the AlxGa1−xN barrier is partially relaxed, the mobility of the 2DEG in the first subband decreases significantly, but there is an increase of mobility in the second subband. We suggest that the scattering from the piezoelectric polarization field modulated by the misfit dislocations at the heterointerface is responsible for the decrease of the 2DEG mobility. Meanwhile, the 2DEG in the second subband leaves farther from the heterointerface than that in the first subband, and thus suffers weaker scattering from the heterointerface roughness and the modulated polarization field. Therefore, the mobility of the 2DEG in the second subband is much higher than that in the first subband. [Copyright &y& Elsevier]