Time-resolved photoluminescence of sub-monolayer InGaAs/GaAs quantum-dot-quantum-well heterostructures

Time-resolved photoluminescence (PL) of sub-monolayer (SML) InGaAs/GaAs quantum-dot-quantum-well heterostructures was measured at 5 K for the first time. The radiative lifetime of SML quantum dots (QDs) increases from 500 ps to 800 ps with the increase of the size of QDs, which is related to the small confinement energy of the excitons inside SML QDs and the exciton transfer from smaller QDs to larger ones through tunneling. The rise time of quantum-dot state PL signal strongly depends on the excitation power density. At low excitation power density, the rise time is about 35 ps, the mechanism of carrier capture is dominated by the emission of longitudinal-optical phonons. At high excitation power density, the rise time decreases as the excitation density increases, and Auger process plays an important role in the carrier capture. These results are very useful for understanding the working properties of sub-monolayer quantum-dot devices.

Gal(1-x)Mn(1-x)Sb grown on GaSb with mass-analyzed low-energy dual ion beam deposition

The Ga1-xMnxSb samples were fabricated by the implantation of Mn ions into GaSb (1 0 0) substrate with mass-analyzed low-energy dual ion beam deposition system, and post-annealing. Auger electron spectroscopy depth profile of the Ga1-xMnxSb samples showed that the Mn ions were successfully implanted into GaSb substrate. Clear double-crystal X-ray diffraction patterns of the Ga1-xMnxSb samples indicate that the Ga1-xMnxSb epilayers have the zinc-blende structure without detectable second phase. Magnetic hysteresis-loop of the Ga1-xMnxSb epilayers were obtained at room temperature (293 K) with alternating gradient magnetometry. (c) 2005 Elsevier B.V. All rights reserved.

Investigation of Mn-implanted n-Si by low-energy ion beam deposition

Mn ions were implanted to n-type Si(0 0 1) single crystal by low-energy ion beam deposition technique with an energy of 1000 eV and a dose of 7.5 x 10(17) cm(-2). The samples were held at room temperature and at 300degreesC during implantation. Auger electron spectroscopy depth profiles of samples indicate that the Mn ions reach deeper in the sample implanted at 300degreesC than in the sample implanted at room temperature. X-ray diffraction measurements show that the structure of the sample implanted at room temperature is amorphous while that of the sample implanted at 300degreesC is crystallized. There are no new phases found except silicon both in the two samples. Atomic force microscopy images of samples indicate that the sample implanted at 300degreesC has island-like humps that cover the sample surface while there is no such kind of characteristic in the sample implanted at room temperature. The magnetic properties of samples were investigated by alternating gradient magnetometer (AGM). The sample implanted at 300degreesC shows ferromagnetic behavior at room temperature. (C) 2004 Elsevier BN. All rights reserved.

Magnetic properties of Mn-implanted n-type Ge

Mn+ ions were implanted into n-type Ge(1 1 1) single crystal at room temperature at an energy of 100 keV with a dose of 3 x 10(16) cm(-2). Subsequent annealing was performed on the samples at 400 degreesC and 600 degreesC in a flowing nitrogen atmosphere. The magnetic properties of the samples have been investigated by alternating gradient magnetometer at room temperature. The compositional properties of the annealed samples were studied by Auger electron spectroscopy and the structural properties were analyzed by X-ray diffraction measurements. Magnetization measurements reveal room-temperature ferromagnetism for the annealed samples. The magnetic analysis supported by compositional and structural properties indicates that forming the diluted magnetic semiconductor (DMS) MnxGe1-x after annealing may account for the ferromagnetic behavior in the annealed samples. (C) 2004 Elsevier B.V. All rights reserved.

Effects of Ag on electrical properties of Ag/Ni/p-GaN ohmic contact

Properties of the Ag/Ni/p-GaN structure at different temperatures are studied by Auger electron spectroscopy, scanning electron microscopy and high resolution x-ray diffraction. The effect of Ag in ohmic contact on the crystalline quality is investigated and the optimized value of annealing temperature is reported. The lowest specific contact resistance of 2.5 x 10(-4) Omega cm(2) is obtained at annealing temperature of 550 degrees C.

Comparison of two kinds of active layers for high-power narrow-stripe distributed feedback laser diodes

Usually GaAs/AlGaAs is utilized as an active layer material in laser diodes operating in the spectral range of 800 850 nm. In this work, in addition to a traditional unstrained GaAs/AlGaAs distributed feedback (DFB) laser diode, a compressively strained InGaAlAs/AlGaAs DFB laser diode is numerically investigated in characteristic. The simulation results show that the compressively strained DFB laser diode has a lower transparency carrier density, higher gain, lower Auger recombination rate, and higher stimulated recombination rate, which lead to better a device performance, than the traditional unstrained GaAs/AlGaAs DFB laser diode.

Aluminium doping induced enhancement of p-d coupling in ZnO

Valence-band type Auger lines in Al doped and undoped ZnO were comparatively studied with the corresponding core level x-ray photoelectron spectrography (XPS) spectra as references. Then the shift trend of energy levels in the valence band was that p and p-s-d states move upwards but e and p-d states downwards with increasing Al concentration. The decreased energy of the Zn 3d state is larger than the increased energy of the 0 2p state, indicating the lowering of total energy. This may indicate that Al doping could induce the enhancement of p-d coupling in ZnO, which originates from stronger Al-O hybridization. The shifts of these states and the mechanism were confirmed by valence band XPS spectra and 0 K-edge x-ray absorption spectrography (XAS) spectra. Finally, some previously reported phenomena are explained based on the Al doping induced enhancement of p-d coupling.

A 1.5 mu m n-type InGaAsP/InGaAsP modulation-doped multiple quantum well DFB laser by MOCVD

1.5 mu m n-type InGaAsP/InGaAsP modulation-doped multiple quantum well (MD-MQW) DFB lasers have been fabricated successfully by low pressure metal organic chemical vapour deposition (LP-MOCVD) technology. The experimental results indicate that n-type MD-MQWs can effectively reduce the threshold Current compared with conventional multiple quantum well DFB lasers. Theoretical analysis indicates that such an effect is due to the much smaller absorption loss and lower Auger recombination, compared with that in an undoped MQW structure. Moreover, the introduction of n-type dopant of suitable levels of concentration in the barrier layers enhances the dynamic characteristics of DFB lasers, due to a coupling between the adjacent quantum well layers and tunnelling-assisted injection, which can reduce the relatively long capture time and increase the effective differential gain 1/X dG/dn .

Comparison of valence band x-ray photoelectron spectrum between Al-N-codoped and N-doped ZnO films

The valence band structures of Al-N-codoped [ZnO:(Al, N)] and N-doped (ZnO:N) ZnO films were studied by normal and soft x-ray photoelectron spectroscopy. The valence-band maximum of ZnO:(Al, N) shifts up to Fermi energy level by about 300 meV compared with that of ZnO:N. Such a shift can be attributed to the existence of a kind of Al-N in ZnO:(Al, N), as supported by core level XPS spectra and comparison of modified Auger parameters. Al-N increased the relative quantity of Zn-N in ZnO:(Al, N), while N-N decreased that of Zn-N in ZnO:N. (c) 2006 American Institute of Physics.

Thermal annealing behaviour of Pt on n-GaN Schottky contacts

The structural evolution and temperature dependence of the Schottky barrier heights of Pt contacts on n-GaN epilayer at various annealing temperatures were investigated extensively by Rutherford backscattering spectrometry, x-ray diffraction measurements, Auger electron spectroscopy, scanning electron microscopy and current-voltage measurements. The temperature dependence of the Schottky barrier heights may be attributed to changes of surface morphology of Pt films on the surface and variation of nonstoichiometric defects at the interface vicinity. Experimental results indicated the degradation of Pt contacts on n-GaN above 600 degreesC.

(Ga,Mn,N) compounds growth with mass-analyzed low energy dual ion beam deposition

The (Ga,Mn,N) samples were grown by the implantation of low-energy Mn ions into GaN/Al2O3 substrate at different elevated substrate temperatures with mass-analyzed low-energy dual ion beam deposition system. Auger electron spectroscopy depth profile of samples grown at different substrate temperatures indicates that the Mn ions reach deeper in samples with higher substrate temperatures. Clear X-ray diffraction peak from (Ga,Mn)N is observed in samples grown at the higher substrate temperature. It indicates that under optimized substrate temperature and annealing conditions the solid solution (Ga,Mn)N phase in samples was formed with the same lattice structure as GaN and different lattice constant. (C) 2003 Elsevier Science B.V. All rights reserved.

Fabrication of novel double-hetero-epitaxial SOT structure Si/gamma-Al2O3/Si

In this paper, we report the fabrication of Si-based double-hetero-epitaxial silicon on insulator (SOI) structure Si/gamma-Al2O3/Si. Firstly, single crystalline gamma-Al2O3(100) insulator films were grown epitaxially on Si(100) using the sources of TMA (Al(CH3)(3)) and O-2 by very low-pressure chemical vapor deposition. Afterwards, Si(100) epitaxial films were grown on gamma-Al2O3 (100)/Si(100) epi-substrates using a chemical vapor deposition method similar to the silicon on sapphire epitaxial growth. The Si/gamma-Al2O3/Si SOL materials are characterized in detail by reflect high-energy electron diffraction, X-ray diffraction and Auger energy spectrum (AES) techniques. The insulator layer of gamma-Al2O3 has an excellent dielectric property. The leakage current is less than 1 x 10(-10) A/cm(2) when the electric field is below 1.3 MV/ cm. The Si film grown on gamma-Al2O3/Si epi-substrates was single crystalline. Meanwhile, the AES depth profile of the SOL structure shows that the composition of gamma-Al2O3 film is uniform, and the carbon contamination is not observed. Additionally, the gamma-Al2O3/Si epi-substrates are suitable candidates as a platform for a variety of active layers such as GaN, SiC and GeSi. It shows a bright future for microelectronic and optical electronics applications. (C) 2002 Elsevier Science B.V. All rights reserved.

GdxSi grown with mass-analyzed low energy dual ion beam epitaxy technique

Semiconducting gadolinium silicide GdxSi samples were prepared by mass-analyzed low-energy dual ion beam epitaxy technique. Auger electron spectroscopy depth profiles indicate that the gadolinium ions are implanted into the single-crystal silicon substrate and formed 20 nm thick GdxSi film. X-ray double-crystal diffraction measurement shows that there is no new phase formed. The XPS spectra show that one type of silicon peaks whose binding energy is between that of silicide and silicon dioxide, and the gadolinium peak of binding energy is between that of metal Gd and Gd2O3. All of these results indicate that an amorphous semiconductor is formed. (C) 2002 Elsevier Science B.V. All rights reserved.

(Ga,Mn,As) compounds grown on semi-insulating GaAs with mass-analyzed low energy dual ion beam depositionw

The (Ga,Mn,As) compounds were obtained by the implantation of Mn ions into semi-insulating GaAs substrate with mass-analyzed low energy dual ion beam deposition technique. Auger electron spectroscopy depth profile of a typical sample grown at the substrate temperature of 250degreesC showed that the Mn ions were successfully implanted into GaAs substrate with the implantation depth of 160 nm. X-ray diffraction was employed for the structural analyses of all samples. The experimental results were greatly affected by the substrate temperature. Ga5.2Mn was obtained in the sample grown at the substrate temperature of 250degreesC. Ga5.2Mn, Ga5Mn8 and Mn3Ga were obtained in the sample grown at the substrate temperature of 400degreesC. However, there is no new phase in the sample grown at the substrate temperature of 200degreesC. The sample grown at 400degreesC was annealed at 840degreesC. In this annealed sample Mn3Ga disappeared, Ga5Mn8 tended to disappear,Ga5.2Mn crystallized better and a new phase of Mn2As was generated. (C) 2002 Elsevier Science B,V. All rights reserved.

MnSi similar to 1.73 grown on silicon with mass-analyzed low energy dual ion beam epitaxy technique

Semiconducting manganese silicide, Mn27Si47 and Mn15Si26, were obtained using mass-analyzed low energy dual ion beam epitaxy technique, Auger electron spectroscopy depth profiles showed that some of the Mn ions were deposited on single-crystal silicon substrate and formed a 37.5 nm thick Mn film, and the other Mn ions were successfully implanted into the Si substrate with the implantation depth of 618 nm. Some samples were annealed in the atmosphere of flowing N-2 at 840 degreesC. X-ray diffraction measurements showed that the annealing was beneficial to the formation of Mn27Si47 and Mn15Si26 (C) 2001 Published by Elsevier Science B.V.