Si 共掺杂和高温退火对(Ga,Mn)As 结构和磁性质的影响

Submitted by zhangdi (zhangdi@red.semi.ac.cn) on 2009-04-13T11:45:31Z

稀磁半导体(Ga,Mn)As和铁磁金属-半导体异质结Fe/GaAs铁磁相变过程的研究

Submitted by zhangdi (zhangdi@red.semi.ac.cn) on 2009-04-13T11:45:31Z

In(Ga)N/GaN���质外延纳米结构的生长以及表征

Submitted by zhangdi (zhangdi@red.semi.ac.cn) on 2009-04-13T11:45:31Z

Fe 和(Ga,Cr)As 薄膜的分子束外延生长及磁学性质

Submitted by 阎军 (yanj@red.semi.ac.cn) on 2010-04-28T14:23:05Z No. of bitstreams: 1 鲁军_博士论文.pdf: 4237580 bytes, checksum: 3a1a5f0ea10b0895d92e102e4cdcf5d0 (MD5)

稀磁半导体（Ga,Mn)As 的超快磁光谱研究

Submitted by 阎军 (yanj@red.semi.ac.cn) on 2010-06-07T02:59:47Z No. of bitstreams: 1 博士学位论文 － 朱永刚.pdf: 3575099 bytes, checksum: cb8ced7665a0624ff54bbfafa2be9c35 (MD5)

稀磁半导体(Ga,Mn)As 中自旋动力学的探索与研究

Submitted by 阎军 (yanj@red.semi.ac.cn) on 2010-07-02T05:55:53Z No. of bitstreams: 1 罗晶：稀磁半导体 (Ga,Mn)As中自旋动力学的探索与研究.pdf: 2131823 bytes, checksum: 74e83e69fc6f6b1c7247db0e1c2a8e51 (MD5)

STUDY ON MICROWAVE CYCLOTRON RESONANCE OF HIGH-MOBILITY GaAs/Al-0.35 Ga-0.65 As TWO-DIMENSIONAL ELECTRON GAS

The properties of electron states in the presence of microwave irradiation play a key role in understanding the oscillations of longitudinal resistance and the zero-resistance states in a high-mobility two-dimensional electron gas(2DEG) in low magnetic field. The properties of electron states in a high-mobility and low-density GaAs/Al0.35Ga0.65As 2DEG in the presence of Ka-band microwave irradiation were studied by reflectance-based optically detected cyclotron resonance(RODCR). The influences of the direction of microwave alternating electronic field, wavelength of the laser, and temperature on RODCR results were discussed. The results show that RODCR measurements provide a convenient and powerful method for studying electron states in 2DEG.

Structure and magnetic property of (Ga,Cr)As films with different Cr contents

We report variations in structure and magnetic property of (Ga,Cr) As films with increasing Cr content x. Due to phase segregation, a tendency towards inhomogeneous distribution with increasing x is confirmed. Barkhausen-like magnetization and large remanent magnetic moment were also clearly observed in the samples with x<5.3%. However, spin-glass-like behaviors were observed in both dc and ac magnetic measurements, which might originate from the competition between magnetic nucleation and frustration of long ferromagnetic order in this inhomogeneous system. All the samples exhibit characteristics of variable-range hopping conductivity at temperature below 150 K. Typical magnetic circular dichroism structure was observed in the sample with x=7.9%.

Domain wall resistance in perpendicular (Ga,Mn) As: Dependence on pinning

We have investigated the domain wall resistance for two types of domain walls in a (Ga,Mn)As Hall bar with perpendicular magnetization. A sizeable positive intrinsic DWR is inferred for domain walls that are pinned at an etching step, which is quite consistent with earlier observations. However, much lower intrinsic domain wall resistance is obtained when domain walls are formed by pinning lines in unetched material. This indicates that the spin transport across a domain wall is strongly influenced by the nature of the pinning.

Easy axis reorientation and magneto-crystalline anisotropic resistance of tensile strained (Ga,Mn)As films

We present a study of magnetic anisotropy by using magneto-transport and direct magnetization measurements on tensile strained (Ga,Mn)As films. The magnetic easy axis of the films is in-plane at low temperatures, while the easy axis flips to out-of-plane when temperature is raised or hole concentration is increased. This easy axis reorientation is explained qualitatively in a simple physical picture by Zeners pd model. In addition, the magneto-crystalline anisotropic resistance was also investigated experimentally and theoretically based on the single magnetic domain model. The dependence of sheet resistance on the angle between the magnetic field and [1 0 0] direction was measured. It is found that the magnetization vector M in the single-domain state deviates from the external magnetic field H direction at low magnetic field, while for high magnetic field, M continuously moves following the field direction, which leads to different resistivity function behaviors.

Carrier capture by threading dislocations in (In,Ga)N/GaN heteroepitaxial layers

Using spatially resolved cathodoluminescence spectroscopy, we investigate the spatial luminescence distribution in a fully strained (In,Ga)N layer, in particular, its correlation with the distribution of threading dislocations (TDs). Regarding the impact of TDs on the luminescence properties, we can clearly distinguish between pure edge-type TDs and TDs with screw component. At the positions of both types of TDs, we establish nonradiative recombination sinks. The radius for carrier capture is at least four times larger for TDs with screw component as for pure edge-type TDs. The large capture radius of the former is due to a spiral-like growth mode resulting in an increase in the In content in the center of the spiral domains in comparison to their periphery.

Role of Ga vacancies in enhancing the leakage current of GaN Schottky barrier ultraviolet photodetectors

The leakage current of GaN Schottky barrier ultraviolet photodetectors is investigated. It is found that the photodetectors adopting undoped GaN instead of lightly Si-doped GaN as an active layer show a much lower leakage current even when they have a higher dislocation density. It is also found that the density of Ga vacancies in undoped GaN is much lower than in Si-doped GaN. The Ga vacancies may enhance tunneling and reduce effective Schottky barrier height, leading to an increase of leakage current. It suggests that when undoped GaN is used as the active layer, it is necessary to reduce the leakage current of GaN Schottky barrier ultraviolet photodetector.

制备稀磁半导体Ga

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Influence of Si doping on magnetic properties of (Ga,Mn)As

We have systematically investigated the magnetic properties of Si-doped (Ga,Mn)As films. When the Si content is low, both Curie temperature (T-C) and carrier density (p) decrease compared with undoped (Ga,Mn)As, whereas a monotonic increase of T-C and p is observed with further increase in the doping content of Si. We discuss the possible mechanism for the changes obtained by different Si doping contents and attribute the results to a competition between the existence of Si-Ga (Si substitutes for Ga site) that acts as a donor and Si-I (Si interstitials) which is in favor of the improvement of ferromagnetism. (C) 2008 Elsevier B.V. All rights reserved.