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Spin splitting of the two-dimentional electron gas (2DEG) in modulation-doped Al[sub 0.22]Ga[sub 0.78]N/GaN heterostructures has been studied by means of magnetotransport measurements at low temperatures and high magnetic fields. The spin splitting is observed in Shubnikov–de Haas oscillations at a magnetic field higher than 5.4 T and a temperature of 1.4 K. The effective g factor g[sup *] is enhanced due to the exchange interaction of the 2DEG at high densities. The ratio of the transverse effective g factor g[sub ⊥][sup *] and the longitudinal effective g factor g[sub ∥][sup *] is g[sub ⊥][sup *]/g[sub ∥][sup *]=2.6 indicating the large difference between g[sub ∥][sup *] and g[sub ⊥][sup *]. It is demonstrated that the anisotropy of the g[sup *] is due to the strong polarization-induced electric field at the heterointerface. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effects of temperature and Ge fractions in high mobility Si/Si1-xGex/Si p-type modulation-doped double heterostructures with Ge fractions of 0.2, 0.25, 0.3, grown by rapid thermal process/very low pressure-chemical vapor deposition, are examined. Hole Hall mobility values of nearly 300 cm2/V s and 8400 cm2/V s are obtained at different temperatures and sheet carrier concentrations for heterostructures with x = 0.3. Hole mobility varies inversely with temperature and directly with Ge fraction.

The various effects caused by the biaxial, as well as the uniaxial strain on the ultraviolet emission efficiencies of c-, as well as m-plane of the [Al.sub.x][Ga.sub.1-x]N films with different Al concentrations are examined. The m-plane films are shown to exhibit the ability to attain higher surface emission efficiency, as compared to the c-plane.

Large-area Au/Pt/n-[In.sub.0.2][Ga.sub.0.8]N Schottky contacts are prepared for photovoltaic devices and their current transport mechanisms with different background carrier concentrations are examined. The thermionic emission is a dominating current transport mechanism at the Pt/n-InGaN interface and Schottky diode fabricated using the low background carrier concentration sample has provided much better Schottky barrier characteristics.

The Al 0.22 Ga 0.78 N/GaN/Al 0.22 Ga 0.78 N multilayer heterostructure photoconductive detectors were designed and fabricated. The influence of AlGaN/GaN interface polarization fields on the properties of the photodetector was investigated. The energy band profile of the heterostructure was approximately calculated. Results indicate that electron and hole wells exist on the GaN sides of the Al 0.22 Ga 0.78 N/GaN/Al 0.22 Ga 0.78 N interfaces. The existence of two-dimensional electron gas was proved by variable temperature Hall measurements. The spectral response shows that the responsivity of the heterostructure photodetector was as high as 43 00 A/W at 355 nm under 3 V bias, which is nearly ten times higher than that of a GaN monolayer structure photodetector. [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]