We measure the effect of two-dimensional electron gas in ZnS0.06Se0.94/Zn0.8Cd0.2Se at low temperature and high magnetic field by SdH measurement. We find the energy gap of ZnS0.06Se0.94/Zn0.8Cd0.2Se When it tends toward 0K by PL measurement. Although we did not observe the persistent photo-conductivity effect in this experiment , it is especially that we can lower temperature at 0.03K. In the low temperature, we can observe more figures of SdH and acquire more exact information of electron concentration and effective mass in the future.

We measure the energy gap of two-dimensional electron gas in AlAs0.56Sb0.44/Ga0.47In0.53As at low temperature by photoluminescence measurement. We intend to observe the intersubband transition in these samples, especially the first and second subband. We have discovered that the sample ( AlAs0.56Sb0.44/Ga0.47In0.53As ) has three subband by SdH and electron density will increase with illumination time. Although we did not observe the intersubband transition in the experiment, we did know the performance and controls about TRIAX320 monochrometer. It means we could measure the better result in further.

We intend to study the properties of two dimensional electron-hole systems in superlattice of ¢»-¢½ semiconductors at ultra-low temperature and high magnetic field by SdH measurement and QHE measurement and to explore the electron¡¦s oscillation varied with the external magnetic field. Considering the sample 2749,the electron densities of the first subband is 2.42¡Ñ1010cm-2,respectively,of which is 2.42¡Ñ1010cm-2 after low temperature¡¦s illumination. Considering the sample 2758,the electron densities of the first subband is 1.236¡Ñ1010cm-2,respectively,of which is 1.236¡Ñ1010cm-2 after low temperature¡¦s illumination. Data are the same, which may be concerned with the quality of the sample.

The two-dimensional electron system in strongly coupled GaAs/Al0.3Ga0.7As double quantum wells has been studied by Shubnikov-de Haas¡]SdH¡^measurements. The degenerate subbands of the double quantum wells are lift into two subbands with a symmetric or anti- symmetric z-direction wave function. We observed that the SdH oscillation due to the second subband of anti-symmetric wave function. The effective mass of the second subband is linearly dependent on the magnetic field range from 0.680 T to 1.964 T. The mass enhancement for the double-quantum-well with an equal well thickness is greater than that with an unequal one. This mass enhancement is attributed to the electron-electron interaction.

Electroreflectance spectra of AlGaN/AlN/GaN heterostructures were measured at various biased voltages (Vdc). Strengths of the internal electric field in AlGaN (FAlGaN) were evaluated from periods of Franz-Keldysh oscillations (FKOs), which were observed above band-gap energy of AlGaN. The relation between FAlGaN and Vdc exhibits an anomalous behavior, which is different from the previous results of the AlGaN/GaN heterostructure. It agrees with the theoretical result of a Poisson-Schrödinger calculation, which shows that two dimensional electron gas (2DEG) exists not only in quantum well (QW) at AlN/GaN interface, but also in QW at AlGaN/AlN interface. This is also consistent with electron-density distribution obtained by capacitance-voltage measurements. When Vdc becomes more negative, the previous mechanism of depleting 2DEG is through flatting one side of QW. However, it was found that the depletion of 2DEG can also occur when the top of valence band at surface becoming higher than bottom at QW.

We have studied the electronic properties of InGaAs/AlInAs nano wire by using Shubnikov-de Hass (SdH)measurement at 0.3K.In order to study the effect of the channel width on the 2DEG,we made the nanometer-scaled 2DEG channels varied with different widths from 700 nm to 1400 nm by focus ion beam. On the AlGaAs/AlInAs nanowires we have studied I-V characteristics with gate-voltage and observed the work range from -3 V to 3 V. After illuminating at 0.3 K, the carrier density of the sample InGaAs-1400 nm increased and observed the persistent photoconductivity effect. After SdH measurement at 0.3 K, we found saturation current of these samples at 77 K but did not observe change with different gate voltage.

We have fabricated the device of High Electron Mobility Transistor(HEMT) on Al0.18Ga0.82N/GaN heterostructures. The mobility of 2DEG of the AlGaN/GaN is 9328 cm2/Vs and carrier concentration is 7.917 1012 cm-2 obtained by conventional van der pauw Hall measurement at temperature of 77 K. We made the conducting channel of nanometer wires on the AlGaN/GaN heterostructures for researching low-dimensional transport of two-Dimensional Electron Gas by gate controlled. From the SdH measurement, we can clearly observe the SdH oscillations and obtain the SdH frequencies. For the sample of 0922GaN-200 nm and 0922GaN-100 nm at 0.39 K,two constituted peaks of Gauss¡¦s function were fitted by Non-linear Curve and Two SdH oscillations beat each other, probably due to spin-splitting. However, we can¡¦t discover any trend in the experiment of gate controlled. In the future, we will try to improve the quality and discover the suitable depth of SiO2.

The recent discovery of a two-dimensional electron (2DEG) gas at interfaces between nonpolar SrTiO₃ (STO) with other polar perovskites has lead to an enormous amount of research. Among this 2DEGs most interesting properties are two-dimensional superconductivity and ferromagnetism, sometimes concurrent. This study provides a starting point in understanding the reconstruction of bulk perovskite t₂[subscript g] bands near a surface or polar interface. First a symmetry constrained [k arrow] · [p arrow] model is developed for an arbitrary pseudocubic bulk perovskite. This [k arrow] · [p arrow] model is applied to studies of bulk STO under external strain and to the Shubnikov - de Haas effect in lightly doped STO to high magnetic fields. Then a simplified electronic structure model is developed for surfaces and interfaces. This model includes non-linear and non-local screening effects by a single polar lattice mode. Generalization of the lattice screening model is discussed. Bonding within a single perovskite layer is then investigated further to understand Rashba interactions and their connection with microscopic material parameters. Next the optical conductivity of quantum confined t₂[subscript g] bands is investigated. Finally some possible future work based on the ideas developed in this thesis are explained. / text

Electroreflectance spectra of AlGaN/GaN heteostructure were measured for various biased voltage (Vbias). There are Franz-Keldysh oscillations (FKOs) exhibiting above band gap of AlGaN, and strength of electric field of AlGaN (FAlGaN) can be evaluated from periods of the FKOs. A positive polarization charge

We have studied the electronic properties of AlxGa1-xN/GaN heterostructures by using Shubnikov¡Vde Haas(SdH) measurement. Two SdH oscillations were detected on the sample of x=0.31, due to the population of the first two subbands with the energy separations of 94.2 meV. For the samples of x=0.22 and x=0.23, two SdH oscillations beat each other, probably due to a finite zero-field spin splitting. The spin-splitting energies are equal to 1.4~5.3 and 4.5 meV . The samples also showed a persistent photoconductivity effect after illuminating by blue light-emitting diode.